II EARTH SCIENCES LIBRARY MANUAL OF PALEONTOLOGY MANUAL OF PALEONTOLOGY FOR THE USE OF STUDENTS WITH A GENERAL INTRODUCTION ON THE PRINCIPLES OF PALEONTOLOGY BY HENRY ALLEYNE NICHOLSON M.D., D.Sc., PH.D., F.R.S.E., F.G.S., &c. PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF ST ANDREWS SECOND EDITION REVISED AND GREATLY ENLARGED IN TWO VOLS. WILLIAM BLACKWOOD AND SONS EDINBURGH AND LONDON MDCCCLXXIX All Rights reserved W35 \ % EARTH SCIENCES LIBRARY .4 * 9 9 ) ' ' PREFACE TO THE SECOND EDITION. THE present edition of this work has not only been entirely revised and largely re-written, but it has been so largely augmented by the addition of new matter, that it may be considered as to all intents and purposes a new book. In the former edition, the final section of the work was devoted to Historical or Stratigraphical Palaeontology ; but this sub- ject has been entirely omitted on the present occasion, as it is most suitably dealt with separately, and it has been treated of in a general manner in the Author's 'Ancient Life-History of the Earth.' As in the former edition, considerably more space has been allotted to the Invertebrata than to the Vertebrata, for reasons which are obvious, and especially upon the ground that palseontological students are, as a rule, much more largely concerned with the former than the latter. An attempt has also been made to give, as far as possible, brief and general definitions of the more important and widely distributed families, or even genera, of the Invertebrata, as well as, to a more limited extent, of the Vertebrata. In carrying out this attempt, however, it is clear that it was necessary to make a rigid selection of material, based upon what might appear to be the relative importance of different types. All conclusions upon this subject must, however, be matters of VI PREFACE TO THE SECOND EDITION. personal opinion, and it is therefore quite likely that some of the forms which have not been alluded to may be thought to be as important and as deserving of notice as those which are actually selected for mention. So far as this point is concerned, the Author can only say that he has acted to the best of his ability, and that he by no means supposes the selection actually made to be ideally perfect. It is hoped that most of the more important additions to our knowledge of the great and rapidly-growing science of Palaeontology will be found to be incorporated, in however condensed a form, in the present edition. In this connec- tion, however, the Author would wish to mention that the greater part of this edition was written in the early part of the year 1878, and that the whole of it was in the hands of the printers before the commencement of the present year. Owing to this fact, though considerable and unexpected delay has occurred in the actual publication of the work, it has arisen that the Author has been unable to avail him- self fully, or at all, of some important palaeontological works and memoirs which were published towards the close of 1878, and in the early part of the present year. Among these may be more especially mentioned the Second Part of the ' Handbuch der Palseontologie,' by Professors Zittel and Schimper ; the memoirs of Munier-Chalmas and Toula upon the Dactyloporidae ; the valuable memoirs by Mr Henry B. Brady upon the Eeticularian Ehizopoda of the Challenger and Arctic Expeditions ; the concluding portions of the ' Beitrage zur Systematik der fossilen Spongien,' by Pro- fessor Zittel ; the treatise of Professor Mobius upon the structure of Eozoon Canadense ; the important Monograph by Angelin upon the Cystideans ; the researches of Mr P. Herbert Carpenter upon the Oral and Apical Systems of the Echinoderms ; the Croonian Lecture by Mr Moseley upon the Structure of the Stylasteridse ; and the valuable papers upon the Dwarf Crocodiles of the Jurassic, by Pro- PKEFACE TO THE SECOND EDITION. vii lessor Owen, and upon the Oolitic Mammals and the Deino- saurian and Sauranodont Eeptiles of North America, by Professor Marsh. The Author may add that he would have considerably modified the section dealing with the so-called " Tabulate Corals," had his investigations into the structure and relationships of these fossils been completed in time. The number of illustrations in the present edition has been largely increased. Most of the new engravings have been drawn by the Author, and have been transferred to the wood by Mr Charles Berjeau. Lastly, the Author has to express his thanks to his friends, Mr Henry B. Brady, F.K.S., Dr Eamsay H. Traquair, F.E.S.E., and Mr E. Etheridge, jun., F.G.S., for much valuable and friendly assistance. UNITED COLLEGE, ST ANDREWS, September 10, 1879. PREFACE TO THE FIRST EDITION. THE object of the present work is to furnish the student of Geology and the general reader with a compendious account of the leading principles and facts of the vast and ever- increasing science of Palaeontology. In carrying out this object, all superfluous details have been rigidly excluded, and the Author has endeavoured to restrict himself entirely to those facts which are absolutely necessary to any one who would study Palaeontology as a department of science, sufficiently distinct to stand alone, and yet most closely con- nected with the sciences of Zoology and Botany on the one hand, and with Geology on the other hand. In the First Part of the work is given a general account of the principles upon which the palseontological observer proceeds. In the Second Part of the work, Palaeozoology, or the past history of the Animal Kingdom, is treated of ; and here much more space has been devoted to the Invertebrate than to the Vertebrate groups upon the ground that it is chiefly, or almost exclusively, with the former that the ordinary palaeontological student has to deal. The Third Part of the work gives a brief and very gen- eral view of Palaeobotany, or the past history of the Vegetable Kingdom. This department of the subject has not been PREFACE TO THE FIRST EDITION. ix treated at any length, partly because the remains of plants are comparatively rare in the stratified series, and partly because ^nothing less than a special treatise would suffice to handle satisfactorily this obscure and difficult branch of the subject. The fourth and concluding portion of the work treats of Historical, or, as it might be called, Stratigraphical, Palae- ontology, namely, of the application of Palaeontology to the elucidation of the succession of the stratified deposits of the earth's crust. This department of the subject has also been very briefly disposed of, not because its intrinsic importance does not warrant a more extended treatment, but because it is the Author's intention, as his leisure will permit, to devote a separate treatise to the consideration of this wide and comparatively independent section of the science. In conclusion, the Author would beg his readers to re- member that there is no science which is growing so rapidly, and which is as yet so comparatively in its infancy, as Palaeontology ; and that there is none in which the con- clusions of to-day are more liable to be vitiated by the discoveries of the morrow. Even whilst these sheets have been going through the press, facts have been brought to light which ought to have found their place in a Manual of this kind, but which have been of necessity altogether passed over, or, at best, have been merely alluded to. For all deficiencies, therefore, arising from this cause, the Author has to beg the kind indulgence of his readers. "With regard to the Illustrations, the Author has grate- fully to acknowledge the kindness of Alfred E. C. Selwyn, Esq., Director of the Geological Survey of Canada, who placed at the Author's disposal a number of engravings of Silurian and Devonian fossils, from the publications of the Survey. The Author has likewise to acknowledge a similar obligation to Principal Dawson, of M'Gill University, Mon- X PREFACE TO THE FIRST EDITION. treal, who kindly permitted the use of several of the illus- trations of his ' Acadian Geology.' A considerable proportion of the engravings, however, are taken from D'Orbigny's beau- tifully illustrated ' Cours Elementaire de Paleontologie/ by an arrangement with the publishers of that work. UNIVERSITY COLLEGE, TORONTO, October 16, 1872. 1 rrrilV-KH CONTENTS OF THE FIEST VOLUME. PART L GENERAL INTRODUCTION. CHAPTER I. PAGE Definition of Palaeontology Definition of the term " fossil" Pro- cesses of fossilisation Definition of "rock" Classification of rocks, 1-0 CHAPTER II. Characters of the Sedimentary rocks Mode of formation of the Sedimentary rocks Definition of the term " formation "- Chief divisions of the Aqueous rocks Mechanically-formed rocks Chemically- formed rocks Organically - formed rocks Chalk Limestone Silica and siliceous deposits Carbon and carbonaceous deposits, .... . 10-27 CHAPTER III. Different Ages of the Aqueous rocks Chronological Succession of the Aqueous rocks Value and nature of Palseontological evidence in determining the position of strata Zones of life Use of the term " contemporaneous," as applied to groups of beds General sequence of phenomena at the close of each Geological period Migrations Differences between the fossils of known contemporaneous strata Geological continuity Relations between the Chalk and the Atlantic Ooze Reappear- ance of similar forms of life under similar conditions Doctrine of " colonies," - 28-55 xil CONTENTS. CHAPTER IV. Causes of the imperfection of the palseontological record Causes of the absence of certain animals as fossils Unrepresented time Unconformity, sequence of phenomena indicated by Lead- ing examples of unconformity Thinning out of beds Sudden extinction of animals Disappearance of fossils, * . . 56-70 CHAPTER V. Conclusions to be drawn from fossils Age of rocks Mode of origin of any fossiliferous bed Fluviatile, lacustrine, and marine deposits Conclusions as to climate, . . . 71-76 CHAPTER VI. Primary divisions of the Animal Kingdom Impossibility of a linear classification Tabular view of the chief divisions of the Animal Kingdom General succession and progression of organic types, 77-94 PART ILPALJEOZQQLOGY. CHAPTER VII. Zoological characters and chief divisions of the Protozoa Relations of the Protozoa to time Characters of the Foraminifera Variations of the test of the Foraminifera Distribution of the Foraminifera in time r Classification of the Foraminifera Types of Foraminifera %ozoon Canadense Receptaculites, 97-128 CHAPTER VIII. Characters of the Radiolaria Polycystina General characters of the Spongida Divisions of Sponges The Horny Sponges The Calcispongise The Stromatoporoids Archseocyathus Siliceous Sponges Hexactinellidee Lithistidse Literature of Protozoa, - . . . . 129-151 CHAPTER IX. General characters and chief divisions of the Ccelenterata Distribu- tion in time of Coslenterate animals Orders of Hydrozoa not- represented as fossils Fossil Medusee and Sea-blubbers CONTENTS. Xlll General characters of the Corynida Hydractinia Labechia Palaeocoryne Corynoides General characters of the Theca- phot-a Dendrograptus Dictyonema Structure and probable affinities of Oldhamia General characters and distribution of the Graptolitidse Structure of a simple Graptolite Reproduc- tion of Graptolites Monoprionidian and Diprionidian forms Characters of the genus Graptolites Didymograptus Tetra- graptus Dichograptus Rastrites Diplograptus Climaco- graptus Dicranograptus Phyllograptus Hydrocorallinse Millepora Stylaster Literature of Hydrozoa, . . . 152-175 CHAPTER X. General facts as to the distribution of the Actinozoa in time Divi- sions of the Zoantharia Characters of Z. malacodermata Characters of Z. sclerobasica, and their distribution in time Nature of a Scleroderinic coral Structure of a simple coral Gemmation and fission amongst corals Deep-sea corals and reef-builders Ancient coral-reefs Divisions and distribution in time of the Zoantharia sclerodermata Aporosa Perforata Tabulata Tubulosa, 176-205 CHAPTER XI. Characters of the Rugosa Recent Rugose corals Operculate corals Families and distribution in time of the Rugosa Characters of the Alcyonaria Tubiporidee Gorgonidse Helioporidae Literature of Actinozoa, 206-223 CHAPTER XII. Characters of the Annuloida Characters of the Echinodermata Distribution of Echinodermata in time General characters of the Echinoidea Structure of the test in Echinoids Spines and tubercles Apical disc Regular and irregular Echinoids Perischoechinidae Distribution of Echinoids in time Chief families of Echinoidea, their characters and distribution, . 224-243 CHAPTER XIII. Characters of the Asteroidea Features distinguishing them from the Echinoidea General structure of a Star-fish The internal and integumentary skeletons Distribution of the Asteroidea in time Families and chief fossil types of the Asteroidea xiv CONTENTS. Agelacrinidae Characters of the Ophiuroidea General struc- ture of an Ophiuroid Their distribution in time, . . 244-259 CHAPTER XIV. Characters of the Crinoidea General structure of the skeleton of a Crinoid Distribution of the Crinoidea in time Families of the Crinoidea, . . *. 260-283 CHAPTER XY. Characters of the Cystoidea Structure of the column, calyx, and appendages of the Cystideans Pectinated rhombs Distribu- tion of the Cystideans in time Chief genera of Cystoidea Pasceolus Sphserospongia Nidulites Cyclocrinus Charac- ters of the Blastoidea Structure of Pentremites Distribution of Blastoidea in time Characters and distribution in time of the Holothuroidea Literature of Echinodermata, . . 286-307 CHAPTER XVI. Characters of the Annulosa Characters of the Annelida Characters of the Tubicola Distribution of the Tubicola in time Cornu- lites Conchicolites Serpulites Trachy derma Spirorbis Serpula Ditrupa Characters of the Errant Annelides Scol- ithus Arenicolites Tracks of Errant Annelides Myrianites Origin of supposed Annelide tracks Literature of Annel- ida, . . ...... . . 308-326 CHAPTER XVII. Characters of Arthropoda Distribution of Arthropoda in time Characters of Crustacea Morphology of a typical Crustacean General facts as to the past existence of Crustacea Table of the divisions of the Crustacea Characters and divisions of the Cir- ripedia Structure of the shell in the Balanidse Distribution of the Balanidse in time Characters and distribution of the Verrucidse Structure of the Pedunculated Cirripedes Dis- tribution of the Lepadidse in time, 327-340 CHAPTER XVIII. Characters and orders of the Entomostracous Crustaceans Ostra- coda Distribution of the Ostracoda in time Estheria Char- acters and distribution in time of the Phyllopoda Characters CONTENTS. XV of the Trilobita General structure of a Trilobite Appendages of Trilobites Systematic position of Trilobites Distribu- tionof Trilobites in past time Leading families of the Trilobita Characters and divisions of the Merostomata Characters and . distribution in time of the Eurypterida Characters and dis- tribution in time of the Xiphosura, 341-386 CHAPTER XIX. Characters of the Malacostraca Characters of the Edriophthalmata Characters and distribution in time of the Amphipoda Characters and distribution in time of the Isopoda Characters of the Podophthalmata Characters and distribution of the Stomapoda Characters and distribution of the Decapoda Macrura Anomura Brachyura Literature of Crustacea, 387-397 CHAPTER XX. Characters of the Arachnida General distribution of the Arachnida in time Characters and distribution of the Scorpionidse Cha- racters and distribution of the Araneida Characters and dis- tribution of the Myriapoda Characters and distribution in time of the Insecta Literature of Arachnida, Myriapoda, and Insecta, 398-409 CHAPTER XXI. General characters of the Moll usca General characters of the shell of the Molluscs General distribution of the Mollusca in time Divisions of the Mollusca Characters of the Polyzoa Struc- ture of the polypides and colonies of the Polyzoa Divisions of the Polyzoa Distribution of the Polyzoa in time Chief fam- ilies of the Polyzoa and their range in time, . . . 410-434 CHAPTER XXII. General characters of the Brachiopoda Structure of the shell of the Brachiopods Oral processes and their supports Divisions of the Brachiopods-: General distribution of the Brachiopoda in time Characters, distribution in time, and leading genera of the Terebratulidae Thecidiidse Spiriferidse Koninckinidse Rhynchonellidae Strophomenidse Productidse Craniadse Discinidse LingulidjB Trimerellidse, . . . . 435-463 XVI CONTENTS. CHAPTER XXIII. General characters of the Lamellibranchiata Shell of the Lamelli- branchs General distribution of the Lamellibranchiata in time Ostreidae Aviculidae Mytilidae Arcadae Trigoniadse Unionidse Chamidae Hippuritidae Tridacnidae Cardiadae Lucinidae Cycladidae Cyprinidse Veneridae Mactridae Tellinidae Solenidae Myacidae Anatinidae Gastrochsenidaa Pholadidae, ...... . 464-511 PAET I. GENERAL INTRODUCTION PALEONTOLOGY. CHAPTER I. INTRODUCTION. DEFINITION OF PALAEONTOLOGY. PALAEONTOLOGY (Gr. palaios, ancient ; onta, beings ; logos, discourse) is the science which treats of the living beings, whether animal or vegetable, which have inhabited this globe at past periods in its history. It is the ancient life- history of the earth, and if its record could ever be com- pleted, it would furnish us with an account of the structure, habits, and distribution of all the animals and plants which have at any time nourished upon the land-surfaces of the globe or inhabited its waters. From causes, however, which will be subsequently discussed, the palseontological record is most imperfect, and our knowledge is interrupted by gaps which not only bear a large proportion to our solid informa- tion, but which in many cases are of such a nature that we can never hope to have them filled. As Zoology, then, treats of the animals now inhabiting the earth, and as Botany treats of the now existing plants, Palaeontology may be considered as the Zoology and Botany of the past. Ptegarding it from this, the only true point of view, some knowledge of Zoology and Botany is essential to VOL. I. A INTRODUCTION. * a prosecution of the study of Palaeontology, and such de- tails of these sciences as may be deemed requisite will be introduced in the proper place. The materials, again, which fall to be studied by the palaeontologist, are drawn entirely from the proper province of the geologist. Fossils are de- rived from rocJcs. It will therefore be necessary to trespass to some extent upon the peculiar domain of the geologist, and to obtain some knowledge of the origin, composition, and mode of occurrence of the rocks from which Palaeontology obtains its materials. Lastly, Palaeontology, apart from its own importance as an independent science, is employed by the geologist to assist him in his determination of the chron- ological succession of the materials which compose the crust of the earth. Palaeontology, therefore, in one of its aspects, is a branch of geological science, and requires separate study in its relation to historical Geology. DEFINITION OF FOSSILS. All the natural objects which come to be studied by the palaeontologist are termed " fossils " (Lat. fossus, dug up). In most cases, fossils, or, as they are often termed, " petri- factions," are actual portions of animal or vegetable organ- isms, such as the shells of Molluscs, the skeletons of Corals, the bones of Vertebrate animals, the wood, bark, or leaves of plants, &c. ; and these may be preserved very much in their original condition, or may have been very much altered by changes subsequent to their burial. Strictly speaking, how- ever, by the term " fossil " is understood " any body, or the traces of the existence of any body, whether animal or vege- table, which has been buried in the earth by natural causes " (Lyell). We shall find, therefore, that we must include under the head of fossils objects which at no time themselves formed parts of any animal or vegetable, but which, never- theless, point to the former existence of such organisms, and enable us to reason as to their nature. Under this head come such fossils as the moulds or " casts " of shells and the footprints left by various animals upon sand or mud. In the great majority of cases fossils are the remains of " FOSSILISATION. 3 animals or plants which are now extinct that is to say, which no longer are in existence, but have entirely disap- peared from the earth's surface. In some cases, however, fossils are the remains of recent animals that is, of animals which are still found in a living condition upon the globe. The term " sub-fossil," sometimes applied to these, has been more appropriately applied in another sense, and is best dis- carded in this connection. In any case, the fact that a given specimen belongs to an extinct species of animal or plant, or that it is referable to some existing form, does not enter in any way whatever into the determination of the question as to whether or not it is truly a fossil. If such a specimen is found in those portions of the earth's crust which we can show by other evidence to have been formed prior to the establishment of the existing terrestrial order, then it is a fossil ; while any remains, even though belonging to the same animal, which are found in deposits which have been formed during the historical period, would properly fall to be studied by the zoologist or the botanist, and would not rightly be termed " fossils." It must be admitted, however, that in approaching the " Eecent " period of the earth's history, it becomes a matter, of difficulty indeed, a matter of impos- sibility to draw any precise line between fossil and recent specimens. The terms " fauna " and " flora " are employed in Palre- ontology much as they are by the naturalist, to mean the entire assemblage of the animals or of the plants respectively belonging to a particular region or a particular time. Thus we may speak of the " fauna " of the Carboniferous Period, or the " flora " of the Tertiary Epoch, or the fauna of the Chalk, or of any other set of beds. FOSSILISATION. The term " fossilisation " may be applied in a general sense to all the processes through which an organic body passes in order to become a fossil. Here we need only consider the three leading forms in which fossils present themselves. In the first instance, the fossil is to all intents and purposes an actual 4 INTRODUCTION. organic remain, being itself a fragment of an animal or plant. Thus we may meet with fcJssil bones, shells, or wood, which may have undergone certain changes, such as would be pro- duced by pressure, by the deprivation of organic matter origi- nally present, or by more or less complete infiltration with mineral matter, but which, nevertheless, are practically the real bodies they represent. As a matter of course, it is in the more modern formations that we find fossils least changed from their primitive condition, but all formations almost con- tain some fossils in which the original structure is more or less completely retained. In the second place, we very frequently meet with fossils in the state of " casts " or moulds of the original organic body. What occurs in this case will be readily understood, if we imagine any common bivalve shell, as an Oyster, or Mussel, or Cockle, embedded in clay or mud. If the clay were sufficiently soft and fluid, the first thing would be that it would gain access to the interior of the shell and would completely fill up the space between the valves. The pres- sure, also, of the surrounding matter would insure that the clay would everywhere adhere closely to the exterior of the shell. If now we suppose the clay to be in any way hard- ened so as to be converted into stone, and if we were to break 'y up the stone, we should obvi- ously have the following state of parts. The clay which filled the shell would form an accu- rate cast of the interior of the shell, and the clay outside would Fig. l.Trigonia longa, showing casts give US ail exact impression Or of the exterior and interior of the shell ? ,1 , n ,1 i vi cast of the exterior of the shell (fig. 1). We should have, then, two casts, an interior and an exterior, and the two would be very different to one another, since the inside of a shell is very unlike the outside. In the case, in fact, of many univalve shells, the interior cast is so unlike the exterior or unlike the shell itself, that it may be difficult to determine the true origin of the former. FOSSILISATION. 5 It only, remains to add that there is sometimes a further complication. If the rock be very porous and permeable by water, it may happen that the original shell is entirely dissolved away, leaving the interior cast loose, like the ker- nel of a nut, within the case formed by the exterior cast. Or it may happen that subsequent to the attainment of this state of things, the space thus left vacant between the inte- rior and exterior cast the space, that is, formerly occupied by the shell itself may be filled up by some foreign min- eral deposited there by the infiltration of water. In this last case the splitting open of the rock would reveal an interior cast, an exterior cast, and finally a body which would have the exact form of the original shell, but which would be really a much later formation, and which would not exhibit under the microscope the minute structure of shell. In the third class of cases we have fossils which present with the greatest accuracy the external form, and even some- times the internal minute structure, of the original organic body, but which, nevertheless, are not themselves truly organic, but have been formed by a " replacement " of the particles of the primitive organism by some mineral substance. The most elegant example of this is afforded by fossil wood which has been " silicified " or converted into flint. In this case we have a piece of fossil wood, which presents the rings of growth and fibrous structure of wood, and which under the microscope exhibits even the minutest vessels which char- acterise ligneous tissue. The whole, however, instead of being composed of the original carbonaceous matter of the wood, is now converted into pure flint. The only explana- tion which can be given of this by no means very rare phenomenon, is that the wood must have undergone a slow process of decay in water holding silica or flint in solution. As each particle of the wood was removed by decay, its place was taken by a particle of flint deposited from the surround- ing water, till ultimately the entire wood was silicified. The replacing substance is by no means necessarily flint, but may be iron-pyrites, oxide of iron, sulphur, malachite, magnesite, talc, &c. ; and it is not uncommon to find many other fossils b INTRODUCTION. besides wood preserved, in this way, such as shells, corals, or sponges. The replacement of the original substance of a fossil by some foreign body is thus a matter of common occurrence, but it is by no means always easy to determine whether or not such replacement has taken place. By far the com- monest mode of replacement is that whereby an originally calcareous skeleton is replaced by silica. This process of " silicification " of the replacement of lime by silica is not only an extremely common one, but it is also a readily intelligible one ; since carbonate of lime is an easily and flint a hardly soluble substance. It is thus easy to understand that originally calcareous fossils, such as the shells of Mol- lusca, or the skeletons of Corals, should have in many cases suffered this change, their carbonate of lime being dissolved away, particle by particle, and replaced by precipitated silica, as they were subjected to percolation by heated or alkaline waters holding silica in solution. When we meet with fossils, such as those alluded to above, which we know to have been originally calcareous, but which we now find, unchanged in form, but converted into flint, then we cannot doubt that we have to deal with cases of " silicification," and that the primitive skeleton of lime has in these cases been slowly, and more or less per- fectly, replaced by silica. We cannot, however, speak in such a positive manner as to fossils which we now find to be composed of flint, but as to the original constitution of which we cannot be certain. We find, namely, some fossils which are of uncertain affinities, and which are sometimes found in a siliceous and sometimes in a calcareous state. If we are not positive as to the zoological position of these fossils, or if they belong to a group of animals in which we find the living forms to possess sometimes a calcareous and sometimes a siliceous skeleton, then it is obviously a matter of extreme difficulty to determine whether the extinct forms were really composed of lime or of flint. In such cases, we must be guided principally by the condition of preservation of the fossils which occur associated with such obscure forms in the same beds ; the fact that the associated remains are FOSSILISATION. 7 converted into flint pointing to the probability that the prob- lematical forms were originally calcareous, and vice versa. In the" case, also, of all fossils which present themselves sometimes in a siliceous and sometimes in a calcareous form, there is always the presumption that the skeleton was origi- nally composed of lime, this presumption being based upon the fact that the conversion of the calcareous skeletons of animals into silica by a process of replacement is an un- questionable, an extremely common, and a readily intelligible occurrence. Until recently, indeed, naturalists never allowed them- selves to contemplate the alternative possibility of an origi- nally siliceous skeleton being replaced by lime ; but we have now high authorities in favour of the view that this anom- alous mode of substitution really does occur occasionally. The only case in which anything like definite proof of this abnormal mode of replacement can be said to have been brought forward is that of some of the fossil sponges found in the chalk. Certain of these sponges agree in their general form and in their microscopic structure with the living Hexactinellid Sponges (such as the Venus's Flower- basket), the skeleton of which is composed of flint, and it is therefore difficult to doubt the possession by the fossil types of a primitively siliceous skeleton. We might, indeed, sup- pose that the fossil sponges in question represented an en- tirely new type of sponge-structure with the form of the living Hexactinellids, but with a calcareous skeleton, and that this skeleton had in the process of fossilisation been often replaced by flint ; but this supposition would be a violent one, and would not be warranted by the known facts. It has, however, been pointed out by Zittel that these sponges are sometimes found in the rocks with their skeleton in part calcareous and in part siliceous ; and the same distinguished observer has further shown that in such specimens the siliceous portions of the skeleton retain their minute micro- scopic character, whereas the calcareous portions have en- tirely lost their minute structure, and are composed simply of crystalline calcite. Had the skeleton been originally calcareous, the lime composing it would have been in a INTRODUCTION. granular and not a crystalline form, and it is therefore very difficult to account for the state of preservation of these speci- mens, unless we admit that the skeleton was primitively silice- ous, and that we have here a case of the substitution of the hardly soluble silica by the easily soluble carbonate of lime. In any case we must carefully distinguish between replace- ment, whether by flint or any other mineral, and infiltration, the latter being merely the process whereby the cavities and natural vacuities of a fossil are liable to become filled by some mineral substance, subsequent to its entombment in sediment. When such a fossil as a shell or a coral, for example, becomes buried in the sandy, calcareous, or argil- laceous mud at the bottom of the sea, the surrounding sediment often does not penetrate into the deeper parts of the fossil, and there are thus left in its interior certain empty spaces, into which the surrounding water makes its way by percolation. Any mineral substances, such as car- bonate of lime or silica, which may be contained in solution in the water, are then liable to undergo precipitation, and to be deposited in a solid form within the fossil. All the natural cavities of a fossil, even down to the minutest microscopic pores or tubes, may in this way become filled with some such infiltrated material, the two commonest agents in this process being lime and flint. If the skeleton of the fossil be a calcareous one, while the infiltrating material has been some less soluble substance, such as silica or some silicate, then the skeleton may be artificially or naturally dissolved away, leaving a cast of the internal cavities of the fossil formed of the infiltrated matter. Thus the minute shells of Foraminifera are often infiltrated with the silicate glau- conite, and exquisitely perfect casts of their interior cavities are subsequently formed by dissolution of the shell itself. In this way, as we shall see hereafter, deposits of green sand have been sometimes produced. DEFINITION OF EOCK. The crust of the earth consists of various different ma- terials, produced at different successive periods, occupying CLASSIFICATION OF ROCKS. 9 certain definite spaces, and not confusedly mixed together, but, on tHe contrary, exhibiting a definite and discoverable order of' arrangement. All these materials, however dif- ferent in appearance, texture, or mineral composition, are called "rocks" by the geologist. The term "rock." then. is to be understood as applying to all the materials which compose the crust of the earth. In the language of geology, the finest mud, the loosest sand, and the most incoherent gravel, are just as much rocks as are the hardest and most compact granites or limestones. CLASSIFICATION OF KOCKS. For the purposes of the palaeontologist all the rocks which enter into the composition of the solid exterior of the earth may be divided into two great classes : 1. The Igneous Eocks, which are formed within the body of the earth itself, and which owe their structure and origin to the action of heat ; and 2. the Aqueous or Sedimentary Eocks, which are formed at the surface of the earth, and which owe their structure to the mechanical action of water. The Igneous Eocks are principally formed below the surface of the earth, are as a general rule destitute of organic remains or fossils, and are mostly in the form of unstratified masses. The Aque- ous and Sedimentary Eocks are formed at the surface by the disintegration and reconstruction of previously existing rocks, or by the vital chemistry of animals or plants, are mostly fossiliferous, and are stratified i.e., are arranged in distinct layers or " strata." The Sedimentary Eocks, as con- taining fossils, are the only rocks which it is essential for the palaeontologist to be acquainted with, and we shall very briefly consider their leading physical characters, their chief varieties, their mode of origin, and their historical succession. /3ft* 1 , i 10 CHAPTEE II. THE FOSSILIFEROUS ROCKS. THE Sedimentary or Fossiliferous Eocks form the greater portion of that part of the earth's crust which is open to our examination, and are distinguished by the fact that they are regularly " stratified/' or arranged in distinct and definite layers or " strata." These layers may consist of a single _material, as in a block of sandstone, or they may consist of different materials. When examined on a large scale, they are always found to consist of alternations of layers of different mineral composition. We may examine any given area,. and find in it nothing but one kind of rock sandstone, perhaps, or limestone. In all cases, however, if we extend our examination sufficiently far, we shall ulti- mately come upon different rocks ; and, as a general rule, the thickness of any particular set of beds is comparatively small, so that different kinds of rock alternate with one another in comparatively small spaces. As regards the origin of the Sedimentary Eocks, they are for the most part " derivative " rocks, being derived from the wear and tear of pre- existent rock. Sometimes, however, they owe their origin to chemical or vital action, when they would more properly be spoken of simply as Aqueous Eocks. As to their mode of deposition, we are enabled to infer that the materials which compose them have formerly been spread out by the action of water, from what we see going on every day at the mouths of our great rivers, and on a smaller scale wherever there is running water. Every stream, where it runs into a lake or into the sea, carries with it a burden of THE FOSSILIFEROUS ROCKS. 11 mud, sand, and rounded pebbles, derived from the waste of the rocks which form its bed and banks. When these materials cease to be impelled by the force of the moving- water they sink to the bottom, the heaviest pebbles, of course, sinking first, the smaller pebbles and sand next, and the finest mud last. Ultimately, therefore, as might have been inferred upon theoretical grounds, and as is proved by practical experience, every lake becomes a recep- tacle for a series of stratified rocks produced by the streams flowing into it. These deposits may vary in different parts of the lake, according as one stream brought down one kind of material and another stream contributed another material; but in all cases the materials will bear ample evidence that they were produced, sorted, and deposited by running water. The finer beds of clay or sand will all be arranged in thicker or thinner layers or laminae ; and if there are any beds of pebbles these will all be rounded or smooth, just like the water-worn pebbles of any brook-course. In all probability, also, we should find in some of the beds the remains of fresh-water shells or plants or other organisms which inhab- ited the lake at the time these beds were being deposited. In the same way large rivers such as the Ganges or Mississippi deposit much of the material which they bring down at their mouths, forming in this way their " deltas." Whenever such a delta is cut through, either by man or by some channel of the river altering its course, we find that it is composed of a succession of horizontal layers or strata of sand or mud, varying in mineral composition, in structure, or in grain, according to the nature of the materials brought down by the river at different periods. Such deltas, also, will contain the remains of animals which inhabit the river, with fragments of the plants which grew on its banks, or bones of the animals which lived in its basin. Lastly, the sea itself irrespective of the materials delivered into it by rivers is constantly preparing fresh stratified deposits by its own action. Upon every coast-line the sea is constantly eating back into the land and reducing its component rocks to form the shingle and sand which we see upon every shore. The materials thus produced are not, 12 INTRODUCTION. however, lost, but are . ultimately deposited elsewhere in the form of new stratified accumulations, in which are buried the remains of animals inhabiting the sea at the time. Whenever, then, we find anywhere in the interior of the land any series of beds having these characters composed, that is, of distinct layers, the particles of which, both large and small, show distinct traces of the wearing action of water whenever and wherever we find such rocks, we are justified in assuming that they have been deposited by water in the manner above mentioned. Either they were laid down in some former lake by the combined action of the streams which flowed into it ; or they were deposited at the mouth of some ancient river, forming its delta ; or they were laid down at the bottom of the ocean. In the first two cases, any fossils which the beds might contain would be the remains of fresh- water or terrestrial organisms. In the last case, the majority, at any rate, of the fossils would be the remains of marine animals. The term " formation " is employed by geologists to express " any group of rocks which have some character in common, whether of origin, age, or composition " (Lyell) ; so that we may speak of stratified and unstratified formations, aqueous or igneous formations, fresh- water or marine formations, and o so on. CHIEF DIVISIONS OF THE AQUEOUS BOCKS. The Aqueous Eocks may be divided into two great sections, the Mechanically- formed and the Chemically-formed, includ- ing under the last head all rocks which owe their origin to vital action, as well as those produced by ordinary chemical agencies. A. MECHANICALLY -FORMED EOCKS. These are all those Aqueous Eocks of which we can obtain proofs that their particles have been mechanically transported to their present site. Thus, if we examine a piece of conglomerate or pud- ding-stone, we find it to be composed of a number of rounded pebbles embedded in an enveloping paste or matrix. The pebbles are worn and rounded, and thus show that they have been subjected to much mechanical attrition, whilst they CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 13 have been mechanically transported for a greater or less distance from the rock of which they originally formed part. In the case of an ordinary sandstone, the component grains of sand are equally the result of mechanical attrition, and have been equally transported from a distance. In the case of still finer rocks, such as shale, the particles have been so much water -worn that their source cannot be recognised, though a microscopical examination would reveal that their edges were all worn and rounded. It follows from this that the mechanically-formed Aqueous Eocks are such as can be* proved to have been derived from the abrasion of other pre- existent rock : hence they are often spoken of as " Derivative Eocks." Every bed, therefore, of any mechanically-formed rock, is an exact equivalent of a corresponding amount of destruction of some older rock. The mechanically-formed Eocks may be divided into the two groups of the Arenaceous or Siliceous Eocks, and the Argillaceous or Aluminous Eocks. In the Arenaceous group are those Aqueous Eocks which are mainly composed of smaller or larger grains of flint or silica. The chief varie- ties are the various kinds of sand and sandstone, grits, and most conglomerates and breccias. In the Argillaceous group are those Aqueous Eocks which contain a certain amount of clay or hydrated silicate of alumina. Under this head come clays, shales, marls, clay-slate, and most flags or flag-stones. B. CHEMICALLY-FORMED EOCKS. In this section are com- prised all those Aqueous Eocks which have been formed by chemical agencies. As many of these chemical agencies, however, are exerted through the medium of living beings, whether animals or plants, we get into this section a number of what may be called " organically -formed " rocks. The most important of the Chemically-formed Eocks are the so- called Calcareous Eocks, comprising all those which contain a large proportion of carbonate of lime, or are wholly made up of this substance ; but there are other rocks, of different composition, which are formed by chemical or organic agency, and which may be briefly noticed. As to the origin of the so-called Calcareous Eocks (Lat. calx, lime), carbonate of lime is soluble in water holding 14 INTRODUCTION. a certain amount of carbonic acid gas in solution; and it is therefore found in larger or smaller quantity dissolved in all natural waters, both fresh and salt, since these waters are always to some extent charged with the above-men- tioned solvent gas. A great number of aquatic animals, however, together with some aquatic plants, are endowed with the power of separating the lime thus held in solu- tion in the water, and of reducing it again to its solid condition. In this way shell-fish, crustaceans, sea-urchins, corals, and an immense number of other animals, are enabled to construct their skeletons ; whilst some plants form hard structures within their tissues in a precisely similar manner. We do meet with some calcareous deposits, such as the " stalactites " and " stalagmites " of caves, the " calcareous tufa " and " travertine " of some hot springs, and the spongy calcareous deposits of so-called " petrifying springs," which are purely chemical in their origin, and owe nothing to the operation of living beings. Such deposits are formed simply ,by the precipitation of carbonate of lime from water, in con- sequence of the evaporation from the water of the carbonic acid gas which formerly held the lime in solution ; but, though sometimes forming masses of considerable thickness, and of geological importance, they do not concern us here. Almost all the limestones which occur in the series of the stratified rocks are, primarily at any rate, of organic origin, and have been, directly or indirectly, produced by the action of certain lime-making animals or plants, or both combined. The pre- sumption as to all the calcareous rocks, which cannot be clearly shown to have been otherwise produced, is that they are thus organically formed ; and in many cases this pre- sumption can be readily reduced to a certainty. There are many varieties of the calcareous rocks, but the following are those which are of the greatest importance : Chalk is a calcareous rock of a generally soft and pulveru- lent texture, and with an earthy fracture. It varies in its purity, being sometimes almost wholly composed of carbonate of lime, and at other times more or less intermixed with foreign matter. Though usually soft and readily reducible to powder, chalk is occasionally, as in the north of Ireland, CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 15 tolerably hard and compact ; but it never assumes the crys- talline aspect and stony density of limestone, except it be in immediate contact with some mass of igneous rock. By mean.s of the microscope, the true nature and mode of for- mation of chalk can be determined with the greatest ease. In the case of the harder varieties, the examination can be conducted by means of slices ground down to a thinness suf- ficient to render them transparent ; but in the softer kinds the rock must be disintegrated under water, and the debris examined microscopically. When investigated by either of these methods, chalk is found to be a genuine organic rock, being composed of the shells or hard parts of innumerable marine__ animals of different kinds, some entire, some frag- mentary, cemented together by a matrix of very finely granular carbonate of lime. Foremost amongst the animal remains which so largely compose chalk are the shells of the minute creatures which will be sub- sequently spoken of under the name of Foraminifera (fig. 2), and which, in spite of their microscopic dimensions, play a more important part in the process of lime-making than perhaps any other of the larger inhabitants of the ocean. As chalk is found in beds of hundreds of feet in thickness, and of great purity, there was long felt much difficulty in satisfactorily accounting for its mode of formation and origin. By the researches of Carpenter, Wyville Thomson, Huxley, Wallich, and others, it has, however, been shown that there is now forming, in the profound depths of our great oceans, a deposit which is in all essential respects identical with chalk, and which is generally known as the "Atlantic ooze," from its having been first discovered in that sea. This ooze is found at great depths (5000 to over 15,000 feet) in both the At- Fig. 2. Section of Gravesend Chalk, examined by transmitted light and highly magnified. Besides the entire shells of Globigerina, Rotalia, and Textulnria, numerous detached chambers of Globi- gerina are seen. (Original.) 16 INTRODUCTION. Fig. 3. Organisms in the Atlanti c Ooze, chiefly Foraminifera (Globigerina and Textiilaria] , with Polycystina and sponge- spicules ; highly magnified. (Original.) lantic and Pacific, covering enormously large areas of the sea-bottom, and it presents itself as a whitish-brown, sticky, impalpable mud, very like greyish chalk when dried. Chem- ical examination shows that the ooze is composed almost wholly of carbonate of lime, and microscopical examination proves it to be of organic origin, and to be made up of the re- mains of living beings. The principal forms of these belong to the Foraminifera, and the commonest of these are the irregularly -chambered shells of Globigerina, absolutely undistin- guishable from the Globigerince which are so largely present in the chalk (fig. 3). Along with these occur fragments of the skeletons of other larger creatures, and a certain propor- tion of the flinty cases of minute animal and vegetable organisms (Polycystina and Diatoms). Though many of the minute animals, the hard parts of which form the ooze, un- doubtedly live at or near the surface of the sea, others, prob- ably, really live near the bottom ; and the ooze itself forms a congenial home for numerous sponges, sea-lilies, and other marine animals which flourish at great depths in the sea. There is thus established an intimate and most interesting parallelism between the chalk and the ooze of modern oceans. Both are formed essentially in the same way, and the latter only requires consolidation to become actually converted into chalk. Both- are fundamentally organic deposits, apparently requiring a considerable depth of water for their accumulation, and mainly composed of the remains of Foraminifera, together with the entire or broken skeletons of other marine animals of greater dimensions. It is to be remembered, however, that the ooze, though strictly representative of the chalk, cannot be said in any proper sense to be actually identical with the formation so called by geologists. A great lapse of time separates the two, and though composed of the remains of CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 17 representative classes or groups of animals, it is only in the case of tlte lowly-organised Globigerince, and of some other organisms of little higher grade, that we find absolutely the same kinds or species of animals in both. Limestone, like chalk, is composed of carbonate of lime, sometimes almost pure, but more commonly with a greater or less intermixture of some foreign material, such as alumina or silica. The varieties of limestone are almost innumerable, but the great majority can be clearly proved to agree with chalk in being essentially of organic origin, and in being more or less largely composed of the remains of living beings. In many instances the organic remains which compose lime- stone are so large as to be readily visible to the naked eye, and the rock is at once seen to be nothing more than an agglomeration of the skeletons, generally fragmentary, of certain marine animals, cemented together by a matrix of carbonate of lime. This is the case, for example, with the so-called " Crinoidal Limestones," and " Encrinital Marbles " with which the geologist is so familiar, especially as occurring in ' great beds amongst the older formations of the earth's crust. These are seen, on weathered or broken surfaces, or still better in polished slabs, to be composed more or less exclusively of the broken stems and detached plates of sea- lilies (Crinoids). Similarly, other limestones are composed almost entirely of the skeletons of corals ; and such old coralline limestones can readily be paralleled by formations which we can find in actual course of production at the present day. We only need to transport ourselves to the islands of the Pacific, to the West Indies, or to the Indian Ocean, to find great masses of lime formed similarly by living corals, and well known to every one under the name of "coral reefs." Such reefs are often of vast extent, both superficially and in vertical thickness, and they fully equal in this respect any of the coralline limestones of bygone ages. Again, we find other limestones such as the cele- brated " Nummulitic Limestone," which sometimes attains a thickness of some thousands of feet to be almost entirely made up of the shells of Foraminifera. In the case of the " Nummulitic Limestone " just mentioned, these shells VOL. I. B 1 8 INTRODUCTION. are of large size, varying from the size of a split pea up to that of a florin. Very many limestones, however, are made up of the calcareous cases of much smaller forms of Fora- minifera, which are so minute as hardly to be visible to the naked eye. In other cases, again, we find limestones to be composed so largely of the shells of various of the true Mollusca, that we may regard them as essentially made up of the skeletons of this class of animals. At the present day, then, limestone is in process of forma- tion by the agency of various animals, amongst which the Corals, the Foraminifera, and the Mollusca are the most important. The same animals have also been the principal agents in building up the great masses of limestone which we now discover in the crust of the earth ; but in the case of the older calcareous rocks we must add to the above the Crinoids, as having formerly contributed on an immense scale to the formation of limestone. NOT are we only to ascribe an organic origin to such limestones as are composed of fossils large enough to be visible to the unassisted eye. On the contrary, most other limestones which at first sight ap- pear compact, more or less crystalline, and nearly devoid of traces of life, are found, when properly examined, to be also composed of the remains of various organisms. All the commoner limestones, in fact, from the Lower Silurian period onwards, can be easily proved to be thus organic rocks, if we investigate weathered or polished surfaces with a lens, or, still better, if we cut thin slices of the rock and grind these down till they are transparent. When thus examined, the rock is usually found to be composed of in- numerable entire or fragmentary fossils, cemented together by a granular or crystalline matrix of carbonate of lime (tigs. 4 and 5). When the matrix is granular, the rock is precisely similar to chalk, except that it is harder and less earthy in texture, whilst the fossils are only occasionally referable to the Foraminifera. In other cases, the matrix is more or less crystalline, and when this crystallisation has been carried to a great extent, the original' organic nature of the rock may be greatly or completely obscured thereby. Thus, in limestones which have been greatly altered or CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 19 " metamorphosed " by the combined action of heat and pres- sure, all traces of organic remains become annihilated, and the rock -becomes completely crystalline throughout. This, Fig. 4. Section of Carboniferous Lime- stone from Spergen Hill, Indiana, U.S., showing numerous large-sized Foraminifera (Kn/kithym) and a few oolitic grains mag- nified. (Original.) Fig. 5. Section of Coniston Limestone (Lower Silurian) from Keisley, Westmor- land ; magnified. The matrix is very coarse- ly crystalline, and the included organic re- mains are chiefly stems of Crinoids. (Ori- ginal.) for example, is the case with the ordinary white " stat- uary marble," slices of which exhibit under the microscope nothing but an aggregate of beautifully transparent crystals of carbonate of lime, without the smallest traces of fossils. There are also other cases, where the limestone is not neces- sarily highly crystalline, and where no metamorphic action in the strict sense has taken place, in which, nevertheless, the microscope fails to reveal any evidence that the rock is organic. Such cases are somewhat obscure, and doubtless depend on different causes in different instances ; but they do not affect the important generalisation that limestones/ are fundamentally the product of the operation of living beings. This fact remains certain ; and when we consider the vast superficial extent occupied by calcareous deposits, and the enormous collective thickness of these, the mind cannot fail to be impressed with the immensity of the period demanded for the formation of these by the agency of such humble and often microscopic creatures as Corals, Crinoids, Forarninifers, and Mollusca. As is the case with the ordinary limestones and marbles, so also the various kinds of magnesian limestone and dolomite 20 INTRODUCTION. are essentially organic in their origin, and are largely made up of the remains of marine animals. Magnesian limestones are, however, very often more or less highly crystalline, and they are very often singularly affected by " concretionary " action, so that their primitive composition and structure is often more or less completely destroyed. " Nor is it only through the agency of animals that lime- stones are built up. Many of the calcareous Alga3 the "Corallines" and " Nullipores " are capable of forming accumulations of lime, sometimes upon a most extensive scale. One of the best examples of a limestone formed principally of the calcareous skeletons of these singular plants is afforded by the so-called " Leitha-Kalk " of the Tertiary series. This limestone is largely composed of nodulated masses, which exhibit no definite structure to the eye, and which were originally set down as " concretions " (fig. 6). Microscopic examination of these apparently inorganic masses shows, however, that we have to deal here with the Fig. Q.Lithothamniiim ramosissimum, a calcareous Alga, from the Leitha-Kalk of the Vienna Basin, a, Portion of a mass, of the natural size ; b and c, Transverse and vertical sections of the same magnified 320 diameters. After Gttmbel. calcareous skeletons of a kind of Nullipore (Litliothamniuni). The Leitha-Kalk is not only extensively developed in the Austro-Hungarian empire, but can be traced through Bosnia into Turkey, and appears to be continued through Asia Minor into Armenia and Persia. Similar calcareous Algae are found in many of the Secondary limestones ; and the Palaeozoic lime- stones will also, doubtless, be found in time to contain the skeletons of these plants to some extent. ', Phosphate of lime is another lime-salt, which is of interest to the palaeontologist. It does not occur largely in the stra- tified series, but it is found in considerable beds l in the 1 Apart from the occurrence of phosphate of lime in actual beds in the strati- fied rocks, as in the Laurentian and Silurian series, this salt may also occur CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 21 Laurentiaji formation, and less abundantly in some later rock -groups, whilst it occurs abundantly in the form of nodules in the parts of the Cretaceous (Upper Greensand) and- Tertiary deposits. Phosphate of lime forms the larger proportion of the earthy matters of the bones of Vertebrate animals, and also occurs in less amount in the skeletons of certain of the Invertebrates (e.g., Lingula, among the Brachio- pods ; Conularia and Theca, among the Pteropods ; and the Crustacea generally). It is, indeed, perhaps more distinctively than carbonate of lime, an organic compound ; and though the formation of many known deposits of phosphate of lime cannot be positively shown to be connected with the previous operation of living beings, there is room for doubt whether this salt is not in reality always primarily a product of vital action. The phosphatic nodules of the Upper Greensand are erroneously called " coprolites," from the belief originally entertained that they were the fossilised excrements of extinct animals ; and though this is not the case, there can be little doubt but that the phosphate of lime which they contain is in this instance of organic origin. 1 The true " coprolites " that is, the petrified excreta of fishes, reptiles, and mammals are also largely composed of phosphate of lime. The last lime-salt which need be mentioned is gypsum, or sulphate of lime. This substance, apart from other modes of occurrence, is not uncommonly found inter stratified with the ordinary sedimentary rocks, in the form of more or less irregular beds ; and in these cases it has a palseontological disseminated through the rock, when it can only be detected by chemical analysis. It is interesting to note that Dr Hicks has recently proved the occurrence of phosphate of lime in this disseminated form in rocks as old as the Cambrian, and that in quantity quite equal to what is generally found to be present in the later fossiliferous rocks. This affords a chemical proof that animal life flourished abundantly in the Cambrian seas. 1 It has been maintained, indeed, that the phosphatic nodules so largely worked for agricultural purposes, are in themselves actual organic bodies or true fossils. In a few cases this admits of demonstration, as it can be shown that the nodule is simply an organism (such as a sponge) infiltrated with phos- phate of lime (Sollas) ; but there are many other examples in which no actual structure has yet been shown to exist, and as to the true origin of which it would be hazardous to offer a positive opinion. 22 INTRODUCTION. importance, as occasionally yielding well-preserved fossils.' Whilst its exact mode of origin is uncertain, it cannot be regarded as in itself an organic rock, though clearly the product of chemical action. To look at, it is usually a whitish or yellowish-white rock, as coarsely crystalline as loaf-sugar, or more so ; and the microscope shows it to be composed entirely of crystals of sulphate of lime. We have seen that the calcareous or lime-containing rocks are the most important of the group of organic deposits ; whilst the siliceous or flint-containing rocks may be regarded as the most important, most typical, and most generally dis- tributed of the mechanically-formed rocks. We have, how- ever, now briefly to consider certain deposits which are more or less completely formed of flint ; but which, nevertheless, are essentially organic in their origin. Flint or silex, hard and intractable as it is, is nevertheless capable of solution in water to a certain extent, and even of assuming, under certain circumstances, a gelatinous or viscous condition. Hence, some hot-springs are impregnated with silica to a considerable extent ; it is present in small quantity in sea-water ; and there is reason to believe that a minute proportion must very generally be present in all bodies of fresh water as well. It is from this silica dissolved in the water that many animals and some plants are enabled to construct for themselves flinty skeletons ; and we find that these animals and plants are and have been sufficiently numerous to give rise to very considerable deposits of siliceous matter by the mere accumulation of their skeletons. Amongst the animals which require special mention in this connection are the microscopic Polycystina. These little creatures are of an extremely low grade of organisation, very closely related to the Foraminifera, but differing in the fact that they secrete a shell or skeleton composed of flint instead of lime. The Polycystina occur abundantly in our present seas ; and their shells are present in some numbers in the fora- miniferal ooze which is found at great depths in the Atlantic and Pacific oceans, being easily recognised by their exquisite shape, their glassy transparency, the general presence of longer or shorter spines, and the sieve- like perforations in CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 23 the walls.. In many places, in fact, especially in the colder portions of the great oceans, or at very great depths, the " Globigerina ooze " disappears, and its place is taken by an ooze composed almost wholly of the shells of Polycystina. Similar deposits, made up of the flinty skeletons of these Eadiolarians, have been formed at previous periods of the earth's history, and now form part of the earth's crust. The two most famous of these deposits occur in Barbadoes and in the Mcobar Islands, the former being well known to workers with the microscope as the " Barbadoes earth " (fig. 7). In addition to flint-producing animals, we have also the great group of fresh -water and marine microscopic plants Fig. 7. Shells of Polycystina from " Barbadoes earth ; " greatly magnified. (Original. ) Fig. 8. Cases of Diatoms in the Rich- mond " Infusorial earth ; " highly magni- fied. (Original.) known as Diatoms, which likewise secrete a siliceous skele- ton, often of great beauty. The skeletons of Diatoms are found abundantly at the present day in lake-deposits, guano, the silt of estuaries, and in the mud which covers many parts of the sea-bottom ; they have been detected in strata of great age ; and in spite of their microscopic dimensions, they have not uncommonly accumulated to form deposits of great thickness, and of considerable superficial extent. Thus the celebrated deposit of " tripoli " (" Polir-schiefer ") of Bohemia, largely worked as polishing-powder, is composed wholly, or almost wholly, of the flinty cases of Diatoms, of which it is calculated that no less that forty-one thousand millions go to make up a single cubic inch of stone. Another celebrated 24 INTRODUCTION. deposit is the so-called " Infusorial earth " of Kichmond in Virginia (fig. 8), where there is a stratum, in places thirty feet thick, composed almost entirely of the microscopic shells of Diatoms. Nodules or layers of flint, or the impure variety of flint known as chert, are found in limestones of almost all ages from the Silurian upwards ; but they are especially abundant in the Chalk. When these flints are examined in thin and transparent slices under the microscope, or in polished sec- tions, they are found to contain an abundance of minute organic bodies such as Foraminifera, sponge- spicules, &c. embedded in a siliceous basis. In many instances the flint contains larger organisms such as a Sponge or a Sea- urchin. As the flint has completely surrounded and infil- trated the fossils which it contains, it is obvious that it must have been deposited from sea-water in a gelatinous condition, and subsequently have hardened. That silica is capable of assuming this viscous and soluble condition is known ; and the formation of flint may therefore be regarded as due to the separation of silica from the sea-water and its deposition round some organic body in a state of chemical change or decay, just as nodules of phosphate of lime or carbonate of iron are produced. The existence of numerous organic bodies in flint has long been known ; but it should be added that a recent observer (Mr Hawkins Johnson) asserts that the existence of an organic structure can be demonstrated by suitable methods of treatment, even in the actual matrix or basis of the flint. 1 In addition to deposits formed of flint itself, there are other siliceous deposits formed by certain silicates, and also 1 It has been asserted that the flints of the chalk are merely fossil sponges. No explanation of the origin of flint, however, can be satisfactory, unless it embraces the origin of chert in almost all great limestones from the Silurian upwards, as well as the common phenomenon of the silicification of organic bodies (such as corals and shells) which are known with certainty to have been originally calcareous. It should also be mentioned that some of the flints of the chalk are certainly only secondarily of organic origin, if even that. This is the case with the tabular masses of flint filling cracks and joints in the chalk. These masses were not produced contemporaneously with the chalk, but have been formed at a later period by the percolation into fissures of the rock of water holding silica in solution. CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 25 of organic ,origin. It has been shown, namely by obser- vations carried out in our present seas that the shells of Foraminifera are liable to become completely infiltrated by silicates (such as " glauconite," or silicate of iron and potash). Should the actual calcareous shell become dis- solved away subsequent to this infiltration as is also liable to occur then, in place of the shells of the For- aminifera, we get a corresponding number of green sandy grains of glauconite, each grain being the cast of a single shell. It has thus been shown by Dr Carpenter that the green sand found covering the sea-bottom in certain localities (as found by the Challenger expedition along the line of the Agulhas current) is really organic, and is composed of casts of the shells of Foraminifera. Long before these observations had been made, it had been shown by Professor Ehrenberg that the green sands of various geological formations are often composed in part of the internal casts of the shells of Foraminifera; and we have thus another and a very interesting example how rock- deposits of considerable extent and of geological importance can be built up by the operation of the minutest living beings. As regards argillaceous deposits, containing alumina or day as their essential ingredient, it cannot be said that any of these have been actually shown to be of organic origin. A recent observation by Sir Wyville Thomson would, how- ever, render it not improbable that some of the great argil- laceous accumulations of past geological periods may be really organic. This distinguished observer, during the cruise of the Challenger, showed that the calcareous ooze which has been already spoken of as covering large areas of the floor of the Atlantic and Pacific at great depths, and which consists almost wholly of the sheila of Foraminif- era, gave place at still greater depths to a red ooze consist- ing of impalpable clayey mud, coloured by oxide of iron, and devoid of traces of organic bodies. As the existence of this widely diffused red ooze, in mid -ocean, and at such great depths, cannot be explained on the supposition that it is a sediment brought down into the sea by rivers, Sir Wyville 26 INTRODUCTION. Thomson came to the conclusion that it was probably formed by the action of the sea-water upon the shells of Foraminifera. These shells, though mainly consisting of lime, also contain a certain proportion of alumina, the former being soluble in the carbonic acid dissolved in the sea -water, whilst the latter is insoluble. There would further appear to be grounds for believing that the solvent power of the sea-water over lime is considerably increased at great depths. If, therefore, we suppose the shells of Foraminifera to be in course of deposition over the floor of the Pacific, at certain depths they would remain unchanged, and would accumulate to form a calcareous ooze ; but at greater depths they would be acted upon by the water, their lime would be dissolved out, their form would disappear, and we should simply have left the small amount of alumina which they previously contained. In process of time this alumina would accumulate to form a bed of clay ; and as this clay had been directly derived from the decom- position of the shells of animals, it would be fairly entitled to be considered an organic deposit. Though not finally established, the hypothesis of Sir Wyville Thomson on this subject is of the greatest interest to the palaeontologist, as possibly serving to explain the occurrence, especially hi the older formations, of great deposits of argillaceous matter which are entirely destitute of traces of life. 1 It only remains, in this connection, to shortly consider the rock- deposits in which carbon is found to be present in greater or less quantity. In the great majority of cases where rocks are found to contain carbon or carbonaceous matter, it can be stated with certainty that this substance is of organic origin, though it is not necessarily derived from vegetables. Carbon derived from the decomposition of > animal bodies is not uncommon ; though it never occurs in such quantity from this source as it may do when it is derived from plants. Thus, many limestones are more or less highly bituminous ; the celebrated siliceous flags or so- 1 Further investigations have thrown doubt upon the above theory, and seem to favour the view that the red ooze is produced by the decomposition of volcanic matter. CHIEF DIVISIONS OF THE AQUEOUS ROCKS. 2*7 called " bituminous schists " of Caithness are impregnated with oily matter apparently derived from the decomposition of the numerous fishes embedded in them ; Silurian shales containing Graptolites, but destitute of plants, are not un- commonly " anthracitic," arid contain a small percentage of. carbon derived from the decay of these zoophytes ; whilst the petroleum so largely worked in North America has not improbably an animal origin. That the fatty compounds present in animal bodies should more or less extensively impregnate fossiliferous rock-masses, is only what might be expected ; but the great bulk of the carbon which exists stored up in the earth's crust is derived from plants ; and the form in which it principally presents itself is that of coal. We shall have to speak again, and at greater length, of coal, and it is sufficient to say here that all the true coals, anthracites, and lignites, are of organic origin, and consist principally of the remains of plants in a more or less altered condition. The bituminous shales which are found so commonly associated with beds of coal also derive their carbon primarily from plants ; and the same is certainly, or probably, the case with similar shales which are known to occur in formations younger than the Carboniferous. Lastly, carbon may occur as a conspicuous constituent of rock-masses in the form of graphite or Hack-lead. In this form it occurs in the shape of detached scales, or of veins or strings, or sometimes of regular layers j 1 and there can be little doubt that in many instances it has an organic origin, though this is not capable of direct proof. When present, at any rate, in quantity, and in the form of layers associated with stratified rocks, as is sometimes the case in the Lau- rentian formation, there can be little hesitation in regarding it as of vegetable origin, and as an altered coal. 1 In the Huroriian formation at Steel River, on the north shore of Lake Superior, there exists a bed of carbonaceous matter which is regularly in- terstratified with the surrounding rocks, and has a thickness of from 30 to 40 feet. This bed is shown by chemical analysis to contain about 50 per cent of carbon, partly in the form of graphite, partly in the form of anthra- cite ; and there can be little doubt but that it is really a stratum of "meta- morphic " coal. 28 CHAPTER III. SUCCESSION OF FORMATIONS CONTEMPORANEITY OF STRATA GEOLOGICAL CONTINUITY. DIFFERENT AGES OF THE AQUEOUS EOCKS. THE two principal tests by which the age of any particular bed, or group of beds, may be determined, are superposition and organic remains a third test sometimes being afforded by mineral characters. The first and most obvious test of the age of any aqueous rock is its relative position to other rocks. Any bed or set of beds of sedimentary origin is obviously and necessarily older than all the strata which surmount it, and younger than all those upon which it rests. It is to be remembered, however, that superposition can at best give us but the relative age of a bed as com- pared with other beds of the same region. It cannot give us the absolute age of any bed ; and if we are ignorant of the age of any of the beds with which we may be deal- ing, we have to appeal to other tests to learn more than the mere order of succession -in the particular region under examination. The second, and in the long-run more available, test of the ages of the different sedimentary beds, is that afforded by their organic remains. Still, this test is also by no means universally applicable, nor in all cases absolutely conclusive. Many aqueous rocks are unfossiliferous through a thickness of hundreds, or even thousands, of feet of little altered sediments ; and even amongst beds which do contain fossils, we often meet with strata of a few feet or yards in DIFFERENT AGES OF THE AQUEOUS ROCKS. 29 thickness, which are wholly destitute of any traces of life. Many fossils, again, range vertically through many groups of strata, and in some cases even through several formations. Such, fossils, therefore, if occurring by themselves, or con- sidered apart from other associated organisms, are not con- clusive as to the age of any particular set of beds. As the result, however, of combined palseontological and geological researches, it is now possible for us to divide the entire series of stratified deposits into a number of definite rock- groups or formations, each of which is characterised by possessing an assemblage of organic remains which do not occur in association in any other formation. Such an assemblage of fossils, characteristic of any given formation, represents the life of the particular period in which the formation was deposited. It follows from this, that when- ever we can get a group or collection of fossils from any particular bed or set of beds, there is rarely any difficulty in determining the precise geological horizon of the beds in which the fossils occur. With certain limitations, however, we may go much further than this. Not only are the great formations characterised by special and characteristic assemblages of animals and plants ; but, in a general way, each subdivision of each for- mation has its own peculiar fossils, by which it may be re- cognised by a skilled worker in palaeontology. Whenever, for instance, we meet in Britain with the fossils known as Graptolites, we may be sure that we are dealing with Silu- rian Eocks. We may, however, go much further than this. If the Graptolites belong to certain genera, we may be sure that we are dealing with Lower Silurian Eocks. Further- more, if certain special forms are present, we may be even able to say to what exact part or subdivision of the Lower Silurian series they belong. All these conclusions, however, would have to be accom- panied by a tacit but well-understood reservation. No Grap- tolites have ever been found in Britain out of rocks known upon other grounds to be Silurian ; but there is no reason why they might not at any time be found in younger de- posits. In the same way, the species and genera which we 30 INTRODUCTION. now regard as characteristic of the Lower Silurians, might at any time be found to have survived into the Upper Silurian period. We should never forget, therefore, in determining the age of a rock by palasontological evidence alone, that we are always reasoning upon generalisations which are the result of experience alone, and which may at any time be overthrown by fresh discoveries. CHRONOLOGICAL SUCCESSION OF THE AQUEOUS EOCKS. As the result of observations made upon the superposition of rocks in different localities, from their mineral characters, and from their included fossils, geologists have been able to divide the entire stratified series into a number of different divisions or formations, each characterised by a general uni- formity of mineral composition, and by a special and peculiar assemblage of organic forms. Each of these primary groups is in turn divided into a series of smaller divisions, charac- terised and distinguished in the same way. It is not pre- tended for a moment that all these primary rock-groups can anywhere be seen surmounting one another regularly. There is no region upon the earth where all the stratified forma- tions can be seen together; and, even when most of them occur in the same country, they can nowhere be seen all succeeding each other in their regular and uninterrupted suc- cession. The reason of this is obvious. There are many places to take a single example where one may see the Silurian Eocks, the Old Eed Sandstone, and the Carboniferous Eocks succeeding one another regularly, and in their proper order. This is because the particular region where this occurs was always submerged beneath the sea while these formations were being deposited. There are, however, many more local- ities in which one would find the Carboniferous Eocks resting unconformably upon the Silurians without the intervention of any strata which could be referred to the Old Eed Sandstone. This might arise from one of two causes : 1. The Silurians might have been elevated above the sea immediately after their deposition, so as to form dry land during the whole of the Old Eed period, in which case, of course, no strata of the CHRONOLOGICAL SUCCESSION OF AQUEOUS ROCKS. 31 V age of the Old Red Sandstone could possibly be deposited. 2. The Old Red Sandstone might have been deposited upon the Silurian, and then the whole might have been elevated above the sea, and subjected to an amount of denudation sufficient to remove the Old Red Sandstone entirely. In this case, when the land was again submerged, the Carbon- iferous Rocks, or any younger formation, might be deposited directly upon Silurian strata. From one or other of these causes, then, or from subsequent disturbances and denuda- tions, it happens that we can rarely find many of the primary formations following one another consecutively and in their regular order. In no case, however, do we ever find the Old Red Sand- stone resting upon the Carboniferous, or the Silurian Rocks reposing on the Old Red. We have therefore, by a compari- son of many different areas, an established order of succession of the stratified formations, as shown in the subjoined ideal section of the crust of the earth (fig. 9). The main subdivisions of the Stratified Rocks are known by the following names : 1. Laurentian 2. Cambrian (with Huronian ?). 3. Silurian. 4. Devonian or Old Red Sandstone. 5. Carboniferous. 6. Permian 1 AT ^ , , , ^ . . > New Red Sandstone. 7. Triassic ) 8. Jurassic or Oolitic. 9. Cretaceous. 10. Eocene. 11. Miocene. 12. Pliocene. 13. Post-tertiary. & M r r 32 INTRODUCTION. IDEAL SECTJON OF THE CRUST OF THE EARTH. Fig. 9. Devonian or Old Hod Sandstone Of these primary groups, the Laurentian, Cambrian, Silu- rian, Devonian, Carboniferous, and Permian are collectively CHRONOLOGICAL SUCCESSION OF AQUEOUS ROCKS. 33 * grouped together under the name of Primary or Palaeozoic, Eocks (Gr. palaios, ancient ; zoe, life), because of the entire divergence of their animals and plants from any now exist- ing upon the globe. The Triassic, Jurassic, and Cretaceous systems are grouped together as the Secondary or Mesozoic formations (Gr. mesos, intermediate ; zoe, life), because their organic remains are intermediate between those of the Pal- aeozoic period, and those of more modern strata. The Eocene, Miocene, Pliocene, and Post-tertiary Eocks are grouped together under the head of Tertiary or Kainozoic Eocks (Gr. kainos, new ; zoe, life), because their organic remains approxi- mate in character to those now existing upon the globe. As regards the division of the entire series of stratified deposits into the above enumerated primary " formations," the value of palaeontological evidence has never been dis- puted. In any given country, it would be possible, un- doubtedly, to determine the order and relative succession of the great formations, to some extent at any rate, by a mere appeal to the mineral character and order of superposition of the rocks themselves ; but it is perfectly clear that this method of procedure would necessarily break down totally the moment we came to try and determine what were the corresponding formations in. some far-distant region. By the stratigraphical evidence alone we could determine the relative position and age, for example, of the Silurian, Devonian, and Carboniferous formations in Britain, but it would be an entire impossibility to identify these same formations, say in North America, except by means of the fossils which they contain. So far, then, as this goes, no question has ever been raised as to the value and powers of Palaeontology ; but when we come to consider the minor rock-groups included in these formations, we find much difference of opinion as to the extent to which the evidence of the fossils is available in determining stratigraphical horizons. Part of this difference of opinion is due to imperfect acquaintance on the part of stratigraphical geologists with the methods of palaeontologi- cal inquiry, and needs no discussion here ; but part is well founded, and either arises from actual defects in the modes of research employed by palaeontologists, or is due to the fact VOL. I. C 34 INTRODUCTION. that the laws of the distribution of fossil organisms are not always the same in different formations, and that they are liable to vary under conditions which are only partially or not at all understood. To both these points our attention may be directed for a few moments. As regards imperfections in the methods of palaeontological research, by far the most important arises from the fact that far too much weight has been attached by observers, espe- cially in the earlier periods of the science, to the age of the rocks in which any given fossil occurred. So long as the opinion was current that fossils occurring in different for- mations must be different, it followed of necessity that the smallest and most trivial varietal or even individual pecu- liarities of form or structure were considered as sufficient to establish specific distinction. At present, however, palaeon- tologists are tolerably agreed that the mere fact of a differ- ence of physical position, and consequently of age, ought never to be taken into account at all in considering the true affinities and systematic position of a fossil. At the same time it is, for many reasons, most important that palaeontolo- gists should have a general personal acquaintance with the rocks in which occur any fossils that they may have to examine and describe ; and many errors have arisen from the neglect of this sound rule. Again, palaeontologists are not agreed as to the relative value of different classes of fossils in determining the age and stratigraphical position of the rocks in which they occur. If all the fossils point towards the same conclusion, there is, of course, no difficulty in the matter ; but it sometimes happens that the vegetable fossils of a given formation would lead one to conclude that it was of a given age, whereas the Invertebrate or Vertebrate fossils would induce us to place it at some different horizon in the stratified series. There has thus arisen a controversy as to the relative value of plants and animals as tests of the age of a given series of rocks ; and in at least two instances this controversy has affected questions of considerable general importance. In one of the cases referred to, we find plants which are ad- mitted to be the same as those of the Coal-measures (Car- CHRONOLOGICAL SUCCESSION OF AQUEOUS ROCKS. 35 boniferous) coexisting with fishes and other animal fossils which are equally admitted to be characteristic of the later formation of the New Eed Sandstone (Permian). This conjunction of an ancient flora with a more modern fauna occurs in the gas -coals of Bohemia, and much difference of opinion has been expressed as to the proper interpreta- tion to be placed upon the facts. If we regard the plants alone, we must place the beds in question in the Carbon- iferous formation, whereas if we look to the animal remains alone, we should with an equal absence of hesitation refer the strata to the Permian. A still more important case of an essentially similar nature occurs in North America, and concerns the boundary-line between the Cretaceous for- mation and the Tertiary, two groups of rocks which in the Old World are separated by an extraordinarily abrupt and conspicuous line of demarcation. In North America we find a series of rocks which contain unquestioned Cretaceous fossils, and another great group of deposits which are charged with an equally unequivocal series of Tertiary fossils ; but between these there is an immense series of beds some four thousand feet in thickness which contains the remains of undoubted Cretaceous Invertebrate and Vertebrate animals mixed with a vast number of regular and unquestionable Tertiary plants. If we look to the animals, we must place this series (known as the " Lignitic Series," from the presence in it of beds of lignite) in the Cretaceous ; whereas from the evidence of the plants alone we should have to consider it as the base of the Tertiary. Upon the whole, however, and without entering into any detailed discussion of the question, it would appear that in all such cases plants have a much smaller value as tests of the geological position and age of the beds in which they occur than may be justifiably at- tached to the remains of the Marine Invertebrates, while these, again, are inferior in this respect to the remains of Vertebrates. Judging by this canon, in which most author- ities are now agreed, the Bohemian gas-coals must be con- sidered as Permian, and the great Lignitic series of North America must be considered as forming the summit of the Cretaceous series. 36 INTRODUCTION. Lastly, there are cases in which the distribution of fossil organisms in different formations differs so much, or presents such peculiarities, that we may reasonably suppose it to have been conditioned by the special circumstances, perhaps now undiscoverable, affecting the deposition of the strata of these formations. Thus, in some cases, as, for example, in the Carboniferous Limestone series, we find that the same fossils characterise the entire series from top to bottom speaking roughly, at any rate and that special kinds of fossils are not restricted to special horizons in the series. This ap- parent diffusion of the same kinds of fossils from the base to the summit of a series of beds perhaps two or three thousand feet in thickness, may of course be simply due to the fact that we have not sufficiently investigated the organic remains met with in the formation, and have not determined with sufficient precision the exact horizons at which each occurs. This is a work of time, and demands both great stratigraphical knowledge and also a wide and accurate acquaintance with the characters of the fossils themselves two requirements rarely fulfilled in the same individual. Still there are reasons for believing that in certain forma- tions, the common and characteristic fossils range from the top to the bottom of the series, so that it would not be pos- sible to determine by means of the fossils the precise position in the series of any given bed. On the other hand, there are cases in which the fossils of a given formation may be divided into two principal groups. In the one group is com- prised a series of common forms of life w^hich may be re- garded as characterising the formation as a whole. In the other group are included certain special fossils which are confined to particular parts of the formation, and which are characteristic of certain definite horizons or zones within the limits of the formation. All the great formations are to some extent capable of being broken up into minor rock- groups, characterised by special life-forms. Some of the differences in the kinds of fossils found in different parts of the same formation must, of course, be simply set down to the fact that different kinds of sediment imply changed con- ditions in the sea, and hence changes in the marine fauna. CHRONOLOGICAL SUCCESSION OF AQUEOUS ROCKS. 37 If, for example, part of a formation consisted of limestone and part of sandstone, we should expect, beforehand, to find that each of these rock-groups would have some fossils not found in the other, since the two would have been formed under different conditions. Apart, however, from differences arising from causes of this nature, we meet with cases in which a formation, even if essentially homogeneous in its mineral nature, can be divided into zones, each of which is characterised by the possession of special groups of fossils. The most celebrated case of this subdivision of a formation by means of its fossils is that afforded by the Lias. This great and essentially argillaceous formation can be divided into a number of zones, each of which is characterised by possessing some special fossils, and particularly by some special Ammonite. These zones are extremely constant, and they are traceable wherever the formation is fully developed, and has been fully examined, in Europe ; so that they enable us to effect a division of the formation into special horizons, which have no stratigraphical existence, and are not separ- ated by any physical break, but which are of the utmost palseontological importance, and which can be rendered readily available in working out the stratigraphy of the formation. Similar " zones " are recognisable in the other Jurassic rocks and in the Cretaceous system ; and it is tolerably certain that in time we shall be able to establish a similar, if less perfect, series of palaeontological divisions in all the great formations. The principal difficulty that we have to confront in deal- ing with these " zones," is to produce any plausible explana- tion accounting for the destruction of the special life-forms of the one zone and the appearance of those of the next zone. For the most part these zones are of very limited vertical extent, and they succeed each other in such a manner as totally to preclude the idea that the dying out of the old forms can have been in any way caused by any physical dis- turbance of the area. Perhaps the most probable view to adopt in the meanwhile is, that the formations in which dis- tinct and limited life-zones can be recognised were deposited with extreme slowness, whereas those which show an essen- 38 INTRODUCTION. tially compact and homogeneous fauna from base to summit were deposited with comparative rapidity. Upon this view, a formation like the Lias is one formed by a process of very slow and intermittent sedimentation, the life -zones being separated by intervals, during which sedimentation must have been at a stand-still, but which were long enough to allow of more or less considerable biological changes, some forms dying out, or becoming modified, while other new ones came in. Upon this view, further, a formation like the Lias, though of comparatively small vertical extent, may represent as long a period of time as the whole of such a great forma- tion as the Carboniferous, which appears to have been formed under conditions of comparatively rapid sedimentation. CONTEMPORANEITY OF STRATA. When groups of beds in different parts of the earth's sur- face, however widely separated from one another, contain the same fossils, or rather an assemblage of fossils in which many identical forms occur, they are ordinarily said to be " contem- poraneous ; " that is to say, they are ordinarily supposed to belong to the same geological period, and to have been formed at the same time in the history of the earth. They would therefore be unhesitatingly regarded as "geological equiva- lents," and would be classed as Silurian, Devonian, Carbon- iferous, and so on. It is to be remembered, however, that it is not necessary, to establish such a degree of equivalency between widely separated groups of strata, that the fossils of each should be to any great extent specifically identical. It is sufficient that, whilst some few species are identical in both, the majority of the fossils should be " representative forms," or, in other words, nearly allied species. It will be shown, however, that groups of strata widely removed from one another in point of distance can only exceptionally be " contemporaneous," in the strict sense of this term. On the contrary, in so far as we can judge from the known facts of the present distribution of living beings, the occurrence of exactly the same fossils in beds far removed from one another is primd facie evidence that the strata are not exactly con- CONTEMPORANEITY OF STRATA. 39 temporaneous, but that they succeeded one another in point of time, though by no long interval geologically speaking. Most of the facts bearing upon this question may be elicited by a consideration of such a widely extended and well-known formation as the Mountain Limestone or Sub-Carboniferous Limestone. This formation occurs in localities as remote from one another as Europe, Central Asia, North America, South America, and Australia ; and it is characterised by an assemblage of well-marked fossils, amongst which Brachio- pods belonging to the genus Product a may be specially singled out. Now, if we believe that the Carboniferous Limestone in all these widely distant localities was strictly contemporaneous, we should be compelled to admit the ex- istence of an ocean embracing all these points, and, in spite of its enormous extent, so uniform in temperature, depth, and the other conditions of marine life, that beings either the same or very nearly the same inhabited it from end to end. We can, however, point to no such uniformity of conditions and consequent uniformity of life over any such vast area at the present day; and we have therefore no right to assume that this is the true explanation of the facts. Indeed this explanation would almost necessarily lead us to the now abandoned theory that each period in geological history was characterised by a special group of organisms spreading over the whole globe, and that there took place at the close of each period a general destruction of all existing forms of life, and a fresh creation of the new forms characteristic of the next period. In our inability, then, to accept this view, we must seek for some other explanation of the observed facts. The most probable view, and the one which is supported most strongly both by what we see at the present day and by what we learn from numerous examples in past time, is this : The Carbon- iferous Limestone was not deposited all over the world in one given period, by one sea, or at exactly the same time ; so that it cannot be said to be strictly " contemporaneous " wherever it is found. This would imply a uniformity of conditions over vast distances, such as exists nowhere at the present day, and such as we have no right to assume ever 40 INTRODUCTION. existed. On the contrary, the deposition of the Carboniferous Limestone must have first taken place in one comparatively limited area say in Europe where fitting conditions were present both for the animals which characterise it, and for the formation of beds of its peculiar mineral and physical characters. How wide this area may have been, signifies very little. It may have been as large as the area now covered by the Pacific, or larger, and yet it could not include all those localities in which strata of Carboniferous age with identical or representative fossils are already known to exist. Under any circumstances, some dispersion of the species of the original Carboniferous area must have been going on by the ordinary processes of migration from the commencement of the Carboniferous period, but this dispersion must have been greatly accelerated towards the close of the period of the deposition of the Carboniferous Limestone. At this time the conditions present in the original area must be supposed to have become unsuitable for the further existence in that area of the assemblage of animals which had been its inhabi- tants, or, at any rate, for a great many of them. The change from suitable to unsuitable conditions must, it is hardly necessary to say, have been an extremely slow and gradual one ; and would doubtless be connected with the progressive shallowing of the sea, the diversion of old currents of heated water, or the incoming of new currents of cold water, or other physical changes tending to alter the climatic conditions of the area. What, then, would be the effect of such a change of conditions as we have supposed upon the animals inhabit- ing the area ? a. Some of them would, doubtless, be suffi- ciently hardy and accommodating to bear up under the new state of things ; and these would persist into the ensuing period, without any perceptible change, it might be, or more probably in the form of varieties or species allied to the old ones. In this case, therefore, we should get a certain num- ber of species which would pass from the Carboniferous Limestone up into the Yoredale Series, the Millstone Grit or the Coal-measures ; or, if we did not find any species exactly the same in all these groups, we should still find in the later groups some forms which would be varieties of CONTEMPORANEITY OF STRATA. 41 those of the older, or which would be allied or representative species. b. There would, in the second place, be a certain number of species which would be utterly unable to withstand the altered conditions of the area ; and these would gradually die out and become wholly extinct. We should thus get a certain number of fossils which would be either exclusively confined to the Carboniferous Limestone in general, or which, perhaps, might not be found out of the Carboniferous Lime- stone of a single region, or even a single particular locality. c. Lastly, some species would yield so far to the altered conditions of the area that they would " migrate," and seek elsewhere a more congenial home. This term is apt to con- vey false impressions ; and it will be well here to consider what is meant by the " migration " of species or groups of animals. It is quite obvious that only animals like birds, mammals, insects, &c., which enjoy when grown up the power of active locomotion, can actually " migrate " in person, supposing they find themselves placed under un- favourable conditions. There are many animals, however, such as most shell-fish, corals, sea-urchins, &c., which have, when adult, either no power of changing their place, or at best a very limited one. Still in these cases even, though the individual has no means of removing his quarters to some more favoured spot, there may be a " migration " of the species from an unsuitable to a suitable locality. This is effected through the medium of the young, which have the power of choosing where they will settle, and are en- dowed with vigorous powers of locomotion. If, for example, a bed of oysters should become placed under conditions unsuitable for the development of these molluscs, it is clear that the old oysters cannot change their location. The young oysters, however, swim , about freely ; and these will move away from the original bed till they find a place which will suit them. By a repetition of this process there may be in course of time a removal or " migration " of a species to almost any distance, irrespective of the fact that the adult is permanently rooted. To return, then, to the case which we have been con- 42 INTRODUCTION. sidering : When the conditions of life in the seas of the Car- boniferous Limestone became unfavourable for the further existence of their fauna, some species would migrate to a more congenial area. In this way a greater or less number of the species characteristic of the Carboniferous Limestone would ultimately be transferred to some other area. Here they would mingle with the forms already inhabiting that area, perhaps more or less completely supplanting these, perhaps merely succeeding in maintaining a more or less precarious existence. In either case, their remains would be preserved in the sedimentary deposits of the new area. When, ages afterwards, we come to examine the crust of the earth geologically, we should find these identical and characteristic species of fossils in the rocks of the two areas, and we should say "these rocks are contemporan- eous." It is clear, however, that we should be wrong in so saying. The rocks in question would belong to the same geological period, but they would belong to different stages of the same period, and they would not be strictly con- temporaneous. For deposits of this nature, believed to hold this relation to each other, the term of " homotaxeous " has been proposed, in place of the term " contemporaneous." What has just been said about the Carboniferous rocks would apply with equal justice to all the great formations, and to many of the smaller rock-groups all over the world. The Silurian rocks of Europe, North America, South America, Australia, &c., contain very similar fossils, and are undoubtedly " homotaxeous." Nothing, however, that we see at the present day can justify us in believing that these widely separated deposits are strictly "contemporaneous," in the sense that they were deposited at exactly the same period of time. We should have to believe, if this conclu- sion is to be justified, that in Silurian times the ocean spread over a much larger area of the earth's surface than it does now, and that its temperature and depth were unnaturally uniform ; and there are, perhaps, some who would accept this view. What has been said about the Silurian rocks as a whole applies with still greater force to certain of the minor subdivisions of the same, which CONTEMPORANEITY OF STRATA. 43 contain many of exactly the same specific forms in parts of the globe very widely removed from one another. It is the very identity of the fossils, however, which proves that the beds in question, from their geographical position, can- not have been deposited at exactly the same time, though they doubtless belong to the same period, and may even be said to be related to one another, as far as the identical fossils are concerned, by lineal descent. Similar remarks might be made about the Devonian, Permian, Triassic, Jurassic, Cretaceous, and other formations ; but it is not necessary further to multiply examples. If we consider the present state of things upon the globe, we shall be further convinced of the justice of these views, which were first prominently brought forward in Britain by Professor Huxley. If we could suddenly remove the sea from the earth, we should find at various points of the earth's surface deposits of different kinds, now concealed from us by the ocean, or only partially known by dredgings or soundings. Thus we should find vast accumulations of calcareous matter, in the form of coral-rock and coral-reef, where now rolls the Pacific Ocean. In high northern and low southern latitudes we should find great deposits of sand and mud, with angular blocks of stone, the whole derived from the ice-clad regions of the poles. Over vast areas, again, in the deep Atlantic, we should find an impalpable chalky mud, or " ooze." All these different deposits are obviously and necessarily " contemporaneous," not only in the geological acceptation of the word, but in its most literal sense. In spite of this fact they would not contain the same fossils; and, indeed, they would be characterised by organic remains which would be wholly different in each case. The coral-reefs of the Pacific would be essentially characterised by the abundance of the remains of reef- building corals, though they would also present other trop- ical forms of life, especially Brachiopods and Echinoderms. The glacial mud of the Polar regions would contain the remains of Arctic molluscs, along with such other animals as delight in severe cold. Lastly, the ooze of the deep Atlantic would contain innumerable Foraminifera, along 44 INTRODUCTION. with siliceous Sponges, Sea-urchins, and Crinoids. We learn, therefore, from this, that contemporaneous deposits not only do not necessarily contain the same fossils, but that, if widely separated geographically, they may be characterised by wholly dissimilar assemblages of organisms. It may happen, again, as pointed out by Sir Charles Lyell, that deposits belonging to different geographical and zoological provinces may, as regards space, be nearly ap- proximated, and, as regards time, may be actually con- temporaneous, and yet may not contain any fossils in com- mon, or only a very few. If, for example, any sudden upheaval were to lay bare what is now the floor of the Red Sea, together with that of the Mediterranean, we should find the two areas to contain deposits actually synchronous as regards the time of their deposition, and very near to one another in point of distance, and yet containing, upon the whole, entirely distinct groups of organic remains. We learn, therefore, from this, that owing to the existence of geographical barriers, it is possible for contemporaneous deposits to be found in close contiguity, in a single region, and yet to contain very different fossils. Again, we know from the researches of Professors Car- penter and Wyville Thomson and Mr Gwyn Jeffreys, that deposits may be formed, side by side, in a single ocean, and may yet differ from one another altogether, both in mineral characters and in their included fossils, though strictly con- temporaneous in point of time. Thus, in parts of the deep Atlantic where the temperature of the bottom water is com- paratively high, we have the calcareous deposit of the ooze, abounding in Foraminifera, Sponges, and Echinoderms. In certain other areas in the same ocean, and in comparatively close contiguity with the preceding, we have the tempera- ture lowered by cold currents, and we find a sandy deposit in process of formation, with a fauna much more scanty than that of the ooze, and wholly distinct from it. We thus learn that sedimentary deposits may be strictly contempo- raneous, and may be placed very near to one another in point of distance, and yet may contain very different fossils. Lastly, synchronous deposits necessarily contain wholly CONTEMPORANEITY OF STRATA. 45 different fossils, if one has been deposited by fresh water, and the other has been laid down in the sea. The fresh- water deposits of one period are obviously contemporaneous with the marine formations of the same period, and they may not be far removed from one another in point of distance, but they must contain altogether different organic remains. The former will contain remains of the fresh- water and ter- restrial animals of the period, and of these only ; whilst the latter will principally, if riot exclusively, be characterised by the remains of marine forms of life. In this way, there is some reason to believe, may be explained the differences between the fossils of the Old Red Sandstone and of the Devonian rocks, strictly so called. Both are believed to have been deposited in the same geological period, and to be truly " contemporaneous ; " but they do not contain the same fossils. This may be readily explained, however, if we sup- pose the former to represent the fresh-water deposits of the Devonian period, or to have been laid down in an inland sea, ^ whilst the latter is the true marine formation of the same period. Under any circumstances, however, we must remember that the doctrine of "homotaxis," if rightly limited and defined, in no way diminishes the value of fossils as indica- tions of the age of the formations in which they occur. If we give the term "contemporaneous" a purely geological sense, and endeavour to forget its literal signification as applying to events which have occurred at precisely the same moment of time, then it is just as good an epithet for the different deposits belonging to a given geological formation as is the term " homotaxeous." All the deposits which possess Carboniferous fossils, at whatever point of the earth's surface they may be situated, belong to the Carboniferous period, and are therefore geologically contemporaneous. All that is really implied by the doctrine of " homotaxis," rightly regarded, is that we cannot say that any great formation in any one country is the precise equivalent of the same forma- tion in any country very widely removed in point of distance, in the sense that its deposition began and ended at exactly the same times ; and therefore we .cannot parallel the sub- 46 INTRODUCTION. divisions of such formations with anything approaching to absolute precision. Kegarded as a whole, however, the Car- boniferous formation of America is the geological equivalent of the Carboniferous formation of Europe, and .both belong to what geologists understand as the " Carboniferous period." As the same is true of all the great formations, in all parts of the world, it is clear that the principal advantage of the use of such a term as " homotaxis " is simply that we thereby avoid the employment of a word which common usage would wrongly interpret ; and it is quite certain that we cannot abolish the idea of geological " contemporaneity," as demon- strated by the presence of identical or representative species of fossils; nor can we refuse to admit that formations con- taining such fossils, however far removed from one another in point of distance, must have been laid down within the limits of the same great " period " in the history of our earth. We are now in a position very briefly to discuss the question of what may be called ."geological continuity." It has already been stated that the entire series of Fossil- iferous or Sedimentary rocks may be naturally divided into a certain number of definite rock-groups or " formations," each of which is characterised by the possession of a peculiar and characteristic assemblage of fossils, constituting, or rather representing, the " life " of the " period " in which the for- mation was deposited. The older geologists held, what probably every one would be tempted to think at first, that the close of each formation was characterised by a general destruction of the forms of life of the period, and that the commencement of each new formation was accom- panied by the creation of a number of new animals and plants, destined to figure as the characteristic fossils of the same. This theory, however, not only invokes forces and processes which it can in no way account for, but overlooks the fact that most of the great formations are separated by lapses of time, unrepresented perhaps by any deposition of rock, or represented only in some particular area, and yet, perhaps, as great as, or greater than, the whole time occupied in the production of the formation itself. CONTEMP-OKANEITY OF STRATA. 47 Nowadays, most geologists hold that there was no such sudden destruction of life at the close of each great geological epoch, and no such creation of fresh forms at the commence- ment of the next period. On the contrary, they hold that there is a geological " continuity," such as we see in other departments of nature, and that the lines which we draw between the great formations merely mark periods of time in which no rocks were laid down, or the rocks deposited in which are at present unknown to us. What are we to believe occurred at the close of any great geological period say, the Cretaceous period ? If we reject the view that the close of the period was marked by a sudden and universal extinction and destruction of the characteristic Cretaceous forms of life, there is only one other view which we can take. Confining our attention solely to those seas of the period of which alone we know enough for safe reasoning, we know that the close of the Cretaceous period in Europe was accompanied, or rather caused, by an upheaval of the Cretaceous area, and an obliteration of the Cretaceous sea. This upheaval was, of course, effected with extreme slowness, or, at any rate, not suddenly, and it must have completely changed the life-conditions or " environment " of the animals which swarmed in the Cretaceous seas. Some of these would doubtless be unable to accommodate themselves to their altered surroundings, and would simply die out. Others, we may presume, would migrate to some more favourable area, and some of these might accomplish their migration without undergoing any change. Most, however, of the forms which migrated, in the process of migration, and by reason of coming into contact with strange neighbours and untried conditions, would probably undergo more or less modification. Ulti- mately, therefore, many characteristic Cretaceous forms might be transferred to some sea far distant from their original home. Not only so, but some of the transferred species might have suffered so much modification that they would no longer be regarded as specifically identical with the original Cretaceous forms, but would be looked upon simply as allied or " representative " species, though really the lineal descendants of the animals of the Chalk. 48 INTRODUCTION. It is perfectly clear that the process of rock-deposition which was going on in Europe towards the close of the Cretaceous period was not, and could not be, abolished by the elevation of the European area, and the obliteration of the Cretaceous sea, but was simply transferred to some other area. In this particular case, we do not happen to know where the new area of deposition may have been. It is quite certain, however, that in whatever area the Cretaceous animals took refuge, there rocks must have been deposited in course of time, as they are in all seas, though it does not in the least follow that the rocks of this new era should have the smallest likeness in mineral composition to the Creta- ceous sediments. If we should at any time discover these rocks, it may pretty safely be predicted what we should find in them in the way of fossils. We should find, namely, some Cretaceous species, probably unchanged ; with these there would be forms allied to the Cretaceous species, but differing from them to a greater or less extent ; in addition, there would be a certain proportion of forms of life wholly unknown in the Cretaceous rocks ; and lastly, there would be a conspicuous absence of certain characteristic species of the Chalk period. In other words, such deposits as we have been speaking of would contain an assemblage of fossils more or less intermediate in character between those of the true Cretaceous period and those of the lowest Tertiary beds (Eocene), which rest upon the Chalk, or they would present an intermixture of Cretaceous with Eocene types. In point of fact, we have fragments of such intermediate deposits (in the Maastricht beds of Holland, the Pisolitic Limestone of France, the Faxoe Limestone of Denmark, and the Thanet Sands of Britain), and we find in them traces of such an intermixture. Moreover, when we come to examine the boundary -line between the Cretaceous and Tertiary in a region far removed from Europe namely, in North America we find that between these two formations, so widely sep- arated in the Old World, we have some four thousand feet of strata (the so-called " Lignitic Series ") containing such a complete intermixture of the forms of life characteristic of these two periods, that it has been a matter of lively con- CONTEMPORANEITY OF STRATA. 49 troversy whether they should be regarded as the summit of the older or the base of the newer series of sediments. We may pause here to consider how it is that we may never hope to find a complete series of deposits linking on one great formation to another, as, for example, the Chalk to the Eocene rocks. In the first place, only a limited portion of the earth has as yet been properly examined, and we have therefore no right to expect that we have as yet hit upon the area, or areas, to which the process of rock-forming was transferred at the close of the Cretaceous period proper in Europe. We have, however, the full right to expect that we shall ultimately find formations which will have to be intercalated in point of time between the White Chalk and the Eocene ; and, as before said, traces of such are already known to us. In the second place, we have every reason to suppose that many of these intermediate deposits have been destroyed at some period subsequent to their formation by what is technically called " denudation," or, in other words, by the action of rain, rivers, ice, and the sea. In the third place, many of the missing deposits may have been concealed since their formation by the deposition upon them of other newer rocks ; or they may be situated in areas which are at present covered by the ocean. Lastly, we must not forget that there may have been times in which great changes in life were actively progressing in areas in which there might be little or no contemporaneous deposition of rock, so that the extreme terms of a series might be preserved to us whilst all the intermediate links might have escaped record. From these and similar causes, it is almost certain that we shall never be able to point to a complete series of deposits linking one great geological period, such as the Cretaceous, to another, such as the Eocene. Still, we may well have a strong conviction that such deposits must exist, or must have existed, as memorials of, at any rate, part of the time which elapsed between the close of the one formation and the com- mencement of the next. Upon any theory of " evolution," at any rate, it is certain that there can be no total break in the great series of the stratified deposits, but that there must have been a complete continuity of life, and a more or less VOL. I. D 50 INTRODUCTION. complete continuity of deposition, from the Laurentian period to the present day. There was, and could have been, no such continuity in any one given area ; but the chain could never have been snapped at one point and taken up at a wholly different one. The links must have been forged in different places, but the chain, nevertheless, remained un- broken. From this point of view, there would be little impropriety in saying that we are living in the Silurian period ; but we could only say so in a very limited sense. While most geologists will readily admit that there must have been such an actual continuity of the great geological periods, from the earliest times up to the present day, it remains certain that we can never dispense with the division of the stratified series into definite rock-groups and life- periods. We can never hope to discover all the lost links of the geological chain, and the great formations will always be separated from one another by more or less evident physical or palseontological breaks, or by both combined. The utmost we can at present do is to arrive at the con- viction that the lines of demarcation between the great formations only mark gaps in our knowledge, and that there can be in nature no hiatus in the long series of fossiliferous deposits. The theory of " geological continuity," then, may in prac- tice be carried so far as to be useless, or even injurious to the progress of science. This would seem to be the case with the attempt to show that we " are still living in the Cretaceous period," and that the ooze now forming at the bottom of the deep Atlantic is merely a continuation in point of time of the great and well-known formation of the White Chalk. The points of resemblance by .which this is sought to be established are these : 1. The Atlantic ooze or " abyssal mud " is a whitish or greyish-looking mud, containing about sixty per cent of carbonate of lime, with from twenty to thirty per cent of silica, and a variable quantity of alumina. When dry, and especially if consolidated, it may fairly be compared in mineral composition to some varieties of Chalk or to Chalk-marl. 2. The abyssal mud of the Atlantic is, to a very large extent composed of the microscopic shells of CONTEMPORANEITY OF STRATA. 51 Foraminfera, some of which are specifically identical with Cretaceous forms, whilst White Chalk is known to be very largely composed of the ddbris of these minute organisms. 3. The ooze contains siliceous sponges, in many respects com- parable to the sponges which are so characteristic of the Cretaceous period. 4. The ooze contains Echinoderms, espe- cially Sea-urchins and Crinoids, such as abounded in the Chalk period ; whilst one of the latter is related to a Creta- ceous type hitherto believed to be extinct. On the other hand, as pointed out by Sir Charles Lyell, Prof. Prestwich, and other observers, the differences between the Atlantic ooze and the Chalk are, to say the least of it, quite as weighty as the resemblances, if not more so. Chalk is composed of from eighty to as much as ninety-nine per cent of carbonate of lime, and has therefore a very small pn>- portion of any siliceous or aluminous impurity. Secondly, the occurrence of identical species of Foraminifera in the two formations amounts to very little ; for it is well known that such lowly organised forms of life have an extraordinary power of persistence, surviving geological changes which are fatal to higher organisms. Moreover, it seems certain that the Foraminifera of the Atlantic ooze are principally derived from the surfaee-waters of the ocean, so that they prove noth- ing as to the depth at which the ooze was deposited. Thirdly, Dr Gwyn Jeffreys, one of the highest of authorities upon the Mollusca, has shown that the Molluscan fauna of the Chalk is essentially a shalloiv-water fauna, and certainly cannot be supposed to have inhabited any very great depth. Lastly, the most characteristic of the Chalk fossils, such as the various forms of Cephalopoda and Bivalve Molluscs, are entirely want- ing in the Atlantic ooze. Prof. Prestwich concludes that although it is probably true that " some considerable portion of the deep sea-bed of the mid-Atlantic has continued submerged since the period of our Chalk, and although the more adaptable forms of life may have been transmitted in unbroken succession through this channel, the immigration of other and more recent faunas may have so modified the old population that the original Chalk element is of no more importance than is the 52 INTRODUCTION. original British element in our own English people. As well might it have been said in the last century that we were living in the period of the early Britons, because their descendants and language still lingered in Cornwall, as that we are living in the Cretaceous period, because a few Creta- ceous forms still linger in the deep Atlantic. Period in Geology must not be confounded with ' system ' or ' forma- tion/ The one is only relative, the other definite. A for- mation is deposited or takes place during a certain time, and that time is the period of the formation ; but a geological period may include several formations, and is defined by the preponderance of certain orders, families, or genera, according to the extent of the period spoken of; and the passage of some of the forms into the next geological series does not carry the period with them, any more than would any par- ticular historical epoch -be delayed until the survivors of the preceding one had died out. Period is an arbitrary time- division. The Chalk or the ' London Clay ' formations mark definite stratigraphical divisions. We may speak of the period of the London Clay, or we may speak of the Tertiary period. It merely refers to the ' time when ' either were in course of construction. The occurrence of Triassic forms in the Jurassic series, of Oolitic forms in the Cretaceous series, and of Cretaceous forms in the Eocene, in no way lessens the independence of each series, although it may sometimes render it difficult to say where one series ceases and the other commences. The land arid littoral faunas are necessarily more liable to change than a deep-sea fauna, be- cause an island or part of a continent may be submerged, and all on it destroyed, while the fauna of the adjacent oceans would survive ; and as we cannot suppose the eleva- tion of entire ocean-beds at the same time, the maritime fauna of one period must be in part almost necessarily trans- mitted to the next." In accordance, therefore, with the principles here laid down, we may conclude that it is not correct to say that we " are living in the Cretaceous period," in any other sense than one might say that we are living in the Silurian period, with this difference, that the Cretaceous period is much nearer CONTEMPORANEITY OF STRATA. 53 to us in point of time than the Silurian, and that we can therefore trace a relationship between certain Cretaceous types and certain living forms that we cannot hope to establish in the case of Silurian fossils. It is to be observed, lastly, that certain classes of animals are always likely to flourish in places and times in which favourable conditions are present, wholly irrespective of any genetic connection between successive faunae. Thus the con- ditions present in the deep Atlantic are such as favour the existence of numerous Foraminifera, Sponges, Echinoderms, &c. Similar conditions existed in the seas in which the Chalk was deposited ; and we need not, therefore, be sur- prised at the predominance of similar organisms in the Cre- taceous period. In the same way, there are portions of the Carboniferous Limestone fairly comparable to the Chalk in mineral characters (making due allowance for difference of age), and containing forms of life which may be regarded as representative of the Cretaceous fauna such as Foramini- fera, smooth Terebratulce, Crinoids, and Sea-urchins. The conditions, however, present in the deep Atlantic are not exactly similar to those under which the Chalk was deposited, for there are certain great classes, such as the Cephalopoda, which abounded in the Cretaceous seas, but which seem to have no representatives in the abyssal mud of the Atlantic. DOCTHINE OF COLONIES. It only remains in this connec- tion to consider very briefly the doctrine of " colonies," laid down by M. Barrande, the eminent Bohemian palaeontologist. It has been laid down as a law that when once a species dis- appears it never again makes its appearance in the geological record. This is unquestionably true, so long as we remember that it can only apply to cases in which a species has entirely and totally disappeared from the earth, and that it is often very difficult, or altogether impossible, to obtain evidence as to the exact time at which a given species has thus become actually extinct. There are plenty of cases in which a species seemingly disappears in a particular set of rocks, to reappear in some higher and later set of rocks in the same region, whilst its remains are wanting in all the intermediate de- posits of the area. It also often occurs that a species, having 54 INTRODUCTION. disappeared in one region, is found in deposits of a later age in another area. The above-mentioned law, therefore, can obviously only hold good of cases in which a species has definitely and finally become extinct; and this implies an amount of knowledge on our part which we seldom or never possess. M. Barrande, however, has pointed out that there are other cases in which groups or species peculiar to one set of beds may appear in a temporary and sporadic manner in a much earlier set of beds, the two deposits thus characterised being separated by beds containing fossils peculiar to the earlier and older series. Thus, the Upper and Lower Silurian rocks of Bohemia are characterised by very distinct assem- blages of fossils. It is found, however, that the Lower Silu- rian rocks contain in places a group of fossils characteristic of the Upper Silurian series. The beds containing this " colony " of Upper Silurian forms are succeeded by strata filled with Lower Silurian fossils ; and it is only after several alternations of this kind that the Upper Silurian fauna comes in definitely and generally. These temporary appearances of a later fauna in the midst of an older fauna are termed by M. Barrande " colonies," and he explains their occurrence as follows : If we suppose the seas of the Bohemian area to have been peopled with Lower Silurian animals at a time when other portions of Europe were covered by a sea contain- ing Upper Silurian animals, and suppose the former area to have been shut off from the latter by a land-barrier, we can readily understand how the " colonies " were produced. If, from any cause, a channel of communication were opened between the Bohemian area and the general area of Northern Europe, an immigration of species would take place from the latter into the former area. The Upper Silurian species of the latter area would thus be imported, in greater or less numbers, into the midst of the general Lower Silurian fauna of Bohemia, and would be preserved in the Lower Silurian rocks. If, however, the channel of communication were speedily closed, so that the new-comers could not be con- stantly reinforced by fresh immigrants, the " colonial " species would die out, and the general Lower Silurian fauna would again reign supreme. A reopening of the channel of com- CONTEMPORANEITY OF STRATA. 55 munication would allow of a fresh immigration and the for- mation of a fresh " colony," and the process might be indefi- nitely repeated. . -Finally, however, we must suppose that the Bohemian area was permanently thrown open to immigration from the general European area, when the Upper Silurian fauna of the latter would succeed in permanently and com- pletely displacing the old Lower Silurian fauna of the former region. The phenomenon, therefore, of " colonies " may be denned as " the coexistence of two general faunas, which, con- sidered in their entirety, are nevertheless distinct ; " and it is to be regarded as merely a case of migration under certain peculiar and exceptional circumstances. It must be borne in mind that the phenomenon of " colonies," even if we regard it as established beyond con- tradiction in the Bohemian area, has never been recognised with any certainty elsewhere, and that it must, under any circumstances, be of very rare and exceptional occurrence. In fact, if " colonies " were at all common, it is quite clear that we should before now have met with plenty of instances of their existence, seeing that we have innumerable examples in which we can show that the migration of marine organisms from one area to another has taken place ; and it is further clear that the occurrence of " colonies " as a common thing would greatly lower the general value of paleeontological evidence as bearing upon the age of fossiliferous strata. 56 CHAPTER IV. THE IMPERFECTION OF THE PAL^ONTOLOGICAL RECORD. As has been already pointed out, the series of the stratified formations is an imperfect one, and is likely ever to remain so. The causes of this " imperfection of the geological record," as it has been termed by Darwin, are various ; but it is chiefly to be ascribed to our as yet incomplete knowledge of the geology of vast areas of the earth's surface, to denuda- tion, and to the fact that many of the missing groups are buried beneath other deposits, whilst more than half of the superficies of the globe is hidden from us by the waters of the sea. The imperfection of the geological record neces- sarily implies an equal imperfection of the " palaeontological record ; " but, in truth, the record of life is far more imperfect than the mere physical series of deposits. As we are here chiefly concerned with the biological aspect of the question, we may advantageously consider some of the main causes of the numerous breaks and gaps in the palaeontological record at some length. I. CAUSES OF THE ABSENCE OF CERTAIN ANIMALS IN Fos- SILIFEROUS DEPOSITS. In the first place, even if the series of the stratified deposits had been preserved to us in its entirety, and we could point to the sedimentary accumula- tions belonging to every period of the earth's history, there would still be enormous deficiencies in the palseontological record, owing to the differences in the facility with which different animals may be preserved as fossils. This subject IMPERFECTION OF PAL^EONTOLOGICAL RECORD. 57 is sufficiently important to render it advisable to consider each of the primary groups of the animal kingdom separately from this point of view : a. Protozoa. As regards the sub-kingdom of the Protozoa, the entire classes of the Gregarinidce and Infusorian Animal- cules, from their absence of hard parts, must ever remain un- represented in a fossil condition. One or two of the latter, however, possess an integumentary covering capable under favourable circumstances of being preserved in rocks of recent age. The Monera present no structures capable of fossilisation ; and the same may be said of the Amcebea, though one or two of the latter have a carapace which might possibly be preserved. The remaining Rhizopodous orders viz., the Foraminifera, Radiolaria, and Spongida almost invariably develop hard structures of lime or flint ; and all these orders, therefore, have left abundant traces of their existence in past time. I. Coelenterata. Amongst the Ccelenterate animals, the Fresh-water Polypes (Hydra) y the Oceanic Hydrozoa, the Jelly-fishes (Medusidce), the Sea-blubbers (Lucernarida), the Sea-anemones (Actinidce), and the CtenopJwra are destitute of hard parts which could be preserved as fossils. The Sea- blubbers, however, supply us with an instance of how a completely soft-bodied creature may leave traces of its past existence ; for there is no doubt that impressions left by the stranded carcasses of these animals have been detected in certain fine-grained rocks (the Lithographic Slate of Solen- hofen). On the other hand, the coralligenous Zoophytes or " corals " (comprising the Zoantharia sclerodermata and sclero- basica, and most of the Alcyonaria) possess hard parts capable of preservation, and the same is the case with most of the Hydroid Zoophytes. Accordingly, there are few more abun- dant fossils than corals ; whilst the large extinct group of the Graptolites is generally placed in the vicinity of the Sea- firs (Sertularians). c. Annuloida. In this sub-kingdom the great class of the Echinodermata may be said to be represented more or less completely by all its orders. In the Sea-cucumbers (Holothur- oidea), however, the calcareous structures so characteristic of 58 INTRODUCTION. the integuments of the other Echinoderms are reduced to their minimum ; and accordingly, the evidence of the past existence of these creatures is of the most scanty description. The other great class of the Annuloida (viz., the Scolecida) comprises animals almost without exception destitute of hard parts, and which mostly live parasitically in the interior of other animals (e.g., the Tape-worms, Suctorial- worms, Round- worms, &c.) We are therefore without any geological evi- dence of the former existence of Scolecida, though no doubt can be reasonably entertained but that the group dates back to a time long anterior to the present fauna. d. Annulosa. Many of the lower Annulose animals, such as Leeches, Earth-worms, and Errant Annelides, possess few or no structures by which we could expect to get direct evidence of their past existence. The last of these, however, have left ample traces of their former presence in the form of burrows or " tracks " upon the mud and sand of ancient sea-bottoms, and are known also by their horny jaws ; while the so - called " Tubicolar " Annelides are well represented by their investing tubes. In the case of the higher An- mdosa, another law steps in to regulate their comparative abundance as fossils. Most, in fact almost all, fossiliferous formations have been deposited in water ; and of necessity, therefore, most fossils are the remains of animals whose habits are naturally aquatic. As most deposits, further, are not only aqueous, but are also marine, most fossils are those of sea-animals. It follows, therefore, that the remains of air-breathing animals, whether these be terrestrial or aerial, can only be preserved in an accidental manner, so to speak ; except the animal inhabit water (as the Cetaceans do), or except in the rare instances in which old land-surfaces have been buried up by sediment, and thus partially kept for our inspection. In accordance with this law, the most important and abundant fossil Annulose animals are Crustaceans ; since these not only have a resisting shell or " exoskeleton," but are also generally aquatic in their habits. The air-breathing classes of the Myriapoda (Centipedes and Millipedes), the Arachnida (Spiders and, Scorpions), and the Insecta or true Insects, on the other hand, have been much less commonly IMPERFECTION OF PAL^EONTOLOGICAL RECORD. 59 and completely preserved, though many of them are perfectly capable of being fossilised. Almost all such remains, how- ever, as we have of these three great classes, are the remains of isolated individuals, which may have been accidentally drowned ; or else they occur in hollow trees, or in fragments of ancient soils, or in vegetable accumulations such as coal and peat. There is, however, a considerable number of aquatic insects (but exclusively in fresh water), and there are many insects the larvae of which inhabit water, whether this be fresh or salt ; so that instances of these occurring as fossils are not very infrequent. e. Mollusca. This sub-kingdom requires little notice, since the greater number of its members possess hard structures / capable of being preserved in a fossil condition. Thus, the horny or calcareous polypidoms of many of the Polyzoa, the shells of the Brachiopods, the true Bivalves, and most of the Gasteropoda, the internal skeletons of the Cuttle-fishes, and the chambered shells of the Tetrabranchiate Cephalopods, all occur more or less abundantly as fossils. The entire class of the Tunicaries, however, presents (with one or two excep- tions) no hard structures, and is hence not with certainty known by any fossil representative. Amongst the Gaster- opoda, again, the Sea-slugs and their allies (Nudibrancliiata) possess no shell, and are unknown to the palaeontologist ; whilst the shell of the Land-slugs is extremely minute, and has not been certainly recognised as fossil. Lastly, the air-breathing terrestrial Molluscs, from their habits, rarely occur as fossils ; whilst those which inhabit rivers, ponds, and lakes are less largely represented than marine forms, owing to the preponderance of salt - water deposits over those of fresh water. /. Vertebrata. The majority of Vetebrate animals possess a bony skeleton, so that their preservation in a fossil state so far as this point is concerned is attended with no diffi- culty. Some of the fishes, however (such as the Lancelot, the Hag-fishes, and the Lampreys), have no scales, and either possess no " endoskeleton " or have one which is almost wholly cartilaginous. The only evidence, therefore, which could be obtained of the past existence of such fishes would 60 INTRODUCTION. be afforded by their teeth ; but these are wanting in the Lancelet, and are very small in the Lampreys : so that we need not wonder that these fishes are unknown as fossils. The higher groups of the fishes, however, taking everything into consideration, may be said to be abundantly represented in a fossil condition by their scales, bones, teeth, and defen- sive spines. The Amphibians are tolerably well represented by their bones and teeth, and, as regards one extinct order, by integumentary plates as well. They have also left many traces of their existence in the form of footprints. Most living Amphibians, however, frequent fresh waters, or spend a great part of their time upon the land ; and hence their remains would not be apt to be preserved in marine deposits. The abundance of Eeptiles as fossils naturally varies much, according to the habits of the different orders. Of the living orders, the Chelonians (Tortoises and Turtles) are by no means rare ; since many of them are habitual denizens of fresh water or of the sea, whilst all are provided with a hard integumentary skeleton. The Snakes are mainly represented by forms which frequented water, and especially by marine forms. The Lizards (Lacertilia) live mainly upon the land, and do not therefore abound as fossils ; but some extinct forms (the Mosasauroids) were marine in their habits, and have consequently been pretty fully preserved. The 'Croco- dilia, again, are so essentially aquatic in their habits, that their comparative frequency in aqueous deposits is no matter of wonder, especially if we recollect that many of the extinct members of this order seem to have frequented the sea itself. Of the extinct orders of Eeptiles, the great Ichthyosauri and the Plesiosauri and their allies were marine in their habits, and their remains occur in what may fairly be called pro- fusion. The Flying Eeptiles, or Pterodactyles, would not seem to have any better chance of being preserved than Birds, if as good, yet their remains occur by no means very \rarely in certain formations. The terrestrial Deinosaurs and Dicynodonts, again, come very much under the laws which regulate the preservation of Mammals as fossils ; and their IMPERFECTION OF PAL^EONTOLOGICAL RECORD. Gl remains are chiefly, but not exclusively, to be found in fluviatile deposits. - As regards Birds, their powers of flight, as pointed out by Sir Charles Lyell, would save them from many destructive agencies, and the lightness of their bones would favour the long floating of the body in water, and thus increase the chances of its being devoured by predaceous animals. In accordance with these considerations the most abundant re- mains of Birds are referable to large wingless forms, to which the power of saving themselves from their enemies by flight was denied, whilst most of their bones were filled with marrow instead of air. Next in abundance after these come the remains of birds which frequent the sea-shore, lakes, ) estuaries, or rivers, or which delight in marshy situations. Lastly, as regards Mammals, the record is far from being a full one, and from obvious causes. The great majority of Mammals live on land, and therefore are not likely to be buried in aqueous, and especially in marine, accumulations. That this cause is the chief one which has operated against the frequent preservation of Mammalian remains is shown by the fact that when we exhume an old land-surface, the re- mains of Mammals may be found in tolerable plenty. The strictly aquatic Mammals such as Whales, Dolphins, and the like are, of course, much more likely ibo have been pre- served as fossils than the strictly terrestrial forms ; but their want of integumentary hard structures places them at a disadvantage in this respect as compared with fishes. In a general way, we may conclude that the preservation of the terrestrial Mammals as fossils is due to the comparatively rare occurrence of a stray individual being killed whilst swimming a river or some other piece of water, or being mired in a bog, or to the bones of one that had died on land being washed into some stream, and thence into a lake or into the sea, by floods ; but there are other cases for which a different explanation must be sought. The most abundant remains of Mammals have been found in deposits which have been laid down in lakes. II. UNREPRESENTED TIME. In the second place, we have seen that the geological record is very imperfect, and this of G2 INTRODUCTION. necessity causes vast gaps in our palseontological knowledge. In this connection we may briefly consider the evidence which we possess as to the immensity of the " unrepresented time " between some of the great formations, and no better example can be chosen than that of the Cretaceous and Eocene rocks, as developed in Europe. In considering such a case, the evidence may be divided into two heads, the one palaeonto- logical, the other purely physical, and each may be looked at separately. The Chalk, as is well known, constitutes in Britain the highest member of the Cretaceous formation, and is the highest deposit there known as appertaining to the great Secondary or Mesozoic series. It is directly overlaid in various places by strata of Eocene age, which form the base of the great Tertiary or Kainozoic series of rocks. The question, then, before us is this, What evidence have we as to the lapse of time represented merely by the dividing-line between the highest beds of the Chalk and the lowest beds of the Eocene ? Taking the palseontological evidence first, it is found that out of five hundred species of fossils known in the Upper Cretaceous beds, only one Brachiopod and a few Foraminifera have hitherto been detected in the immediately overlying Eocene beds. These latter, on the contrary, are replete with organic remains wholly distinct from those of the Cretaceous beds. It may be said, therefore, that the very, extensive as- semblage of animals which lived in the later Cretaceous seas of Britain had entirely passed away and become a thing of the past, before a single grain of the Eocene rocks had been deposited. Now it is of course open to us to believe that the animals of the Chalk sea were suddenly extinguished by some natural agencies unknown to us, and that the animals of the Eocene sea had been in as sudden and as obscure a manner introduced en masse into the same waters. This theory, however, calls upon the stage forces of which we know nothing, and is contradicted by the whole tenor of the operations which we see going on around us at the present day. It is preferable, therefore, to believe that no such violent processes of destruction and re-peopling took place, IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 63 but that the marked break in the life of the two periods in- dicates an enormous lapse of time. The Cretaceous animals, in consequence of the elevation of the British area at the close of the Cretaceous period, must have mostly migrated, some doubtless perishing, and others probably becoming modified in the process. When the British area became once more submerged beneath the sea, and became again a fitting home for marine life, an immigration into it would set in from neighbouring seas. By this time, however, the Cretaceous animals must have mostly died out, or must have become greatly changed in their characters ; and the new immigrants would be forms characteristic of the Lower Eocene. How long the processes here described may have taken, it is utterly impossible to say, even approximately. Judging, however, from what we can observe at the present day, the palseontological break between the Chalk and the Eocene indicates a perfectly incalculable lapse of time ; for all species change or die out slowly, marine species especially so ; and we have here the disappearance of a large fauna almost in its entirety, and its replacement by another wholly distinct. In the second place, to come to the physical evidence, the Eocene strata in Britain are seen to rest upon an eroded and denuded surface of Chalk, filling up " pipes " and winding hollows which descend far below the general surface of the latter. Not only so, but the base of the Eocene rocks is commonly composed of a bed of rolled and rounded flints, derived from the Chalk, affording incontestable proof that the Chalk had been greatly worn down and removed by denudation before the Eocene beds were deposited upon its surface. In short, the Eocene rocks repose "unconform- ably " upon the Chalk, and this, as is well known, indicates the following series of phenomena : Firstly, the Chalk was deposited in horizontal layers at the bottom of the Cretaceous sea. Secondly, at some wholly indefinite time after its deposition, after it had become more or less consolidated, the Chalk must have been raised by a gradual process of elevation above the level of the sea, during which it would inevitably suffer vast denudation. Thirdly, after another 64 INTRODUCTION. wholly indefinite period, the Chalk was again submerged beneath the sea, in which process it would be subjected to still further denudation, and an approximately level surface would be formed upon it. Fourthly, strata of Eocene age were deposited upon the denuded surface of the Chalk, filling up all the hollows and inequalities of its eroded sur- face (fig. 10). Fig. 10. Section showing strata of Tertiary age a , resting upon a worn and denuded surface of White Chalk (Z>), the stratification of which is marked by lines of flints. Iii the unconforrnability, then, between the Chalk and the Eocene rocks, we have unequivocal evidence irrespective of anything that we learn from Palaeontology that the break between the two formations was one of enormous length. In Britain the interval of time thus indicated is not represented by any deposits ; and in Europe generally there are but fragmentary traces of such. We may be quite sure, how- ever, that during the time represented in Britain by the mere line of unconformability between the Chalk and the Eocene, there were somewhere deposited considerable accu- mulations of sediment. Whether we shall ever succeed in discovering these, or any part of these, is, of course, uncer- tain. We may be certain, however, that such deposits, if ever discovered, will prove to be charged with the remains of animals more or less intermediate in character between those of the Cretaceous and those of the Eocene period ; and the huge gap now existing between these formations will thus be more or less completely bridged over. Indeed, in North America we actually find such a series of deposits, IMPERFECTION OF PAL^ONTOLOGICAL RECORD. 65 characterised by a transitional series of fossils, lying between the highest undoubted Cretaceous and the lowest unques- tioned Tertiary strata. The deposits in question the so- called " Lignitic Series " are very thick, and the inter- mixture of Secondary and Tertiary types of life which they exhibit is so complete, that it has been found a matter of great difficulty to assign them definitely either to the Cretaceous or to the Eocene. Amongst other well-known instances of more or less general unconformity in the stratified series, may be men- tioned that between the Lower and Upper Silurian (not al- ways present), that between the Lower and Upper Old Eed Sandstone (also not universal), that between the Carbonif- erous and Permian rocks, that between the Permian and Triassic rocks (not universal), and that between the Lower and Upper Cretaceous rocks. All these physical breaks are accompanied by more or less extensive palaeontological breaks as well. Other breaks which are rendered less important by the absence or scarcity of fossils, or which are as yet not thoroughly established, are those between the Lower and Upper Laurentian rocks, the Upper Laurentian and Huro- nian, and the Upper Cambrian and Lower Silurian. It may not be out of place to point out that the uncon- formabilities here indicated must in no way be confounded with the common cases in which beds of one age rest uncon- formably upon beds far older than themselves. When, for example, we find beds of Carboniferous age reposing uncon- formably upon Silurian strata, this merely indicates that, in the particular locality under examination, the Devonian or Old Ked Sandstone is amissing. This absence of a whole formation in any given region merely indicates that the area was dry land during the period of that formation, or that if any rocks of this age were deposited in this locality, they were removed by denudation before the higher group was laid down. The instances above spoken of, as where the Carboniferous rocks are succeeded unconformably by the Permian, though essentially of the same nature, are distin- guished by an important point. In the former case we know what formation is wanting, and we can intercalate it from VOL. I. E 66 INTRODUCTION. i foreign areas, and thus complete the series. In the latter case we have two successive formations in unconformable junction, and we are not acquainted with any intermediate group of strata which could be intercalated from any other locality. From the above facts, then, we learn that one of the chief causes of the imperfection of the palasontological record is to be found in the vast spaces of time which separate most of the great " formations," and which, so far as we yet know, are not represented by any formation of rock. In process of time we shall doubtless succeed in finding deposits to account for more or less of this " unrepresented time/' but much will ever remain for which we cannot hope to find the representative sediments. It only remains to add that we have ample evidence within the limits of each formation, and wholly irrespective of any want of conformity, of such lengthened pauses in the work of deposition as to have al- lowed of great zoological changes in the interim, and to have thus caused irremediable blanks in the palseontological record. The work of rock-deposition is at best an intermittent pro- cess ; the changes in a fauna, if slowly effected, are continu- ous. Thus there are scores of instances in which the fauna of a given bed, perhaps but a few inches in thickness, differs altogether from that of the beds immediately above and below, and is characterised by species peculiar to itself. In such cases we can only suppose, that though no physical break can be detected, the deposition of sediment was inter- rupted by pauses of incalculable length, during which no additional material was added to the sea-bottom, whilst time was allowed for the dying out of old species and the coming in of new. The incessant repetition of such intervals of un- represented time throughout the whole stratified series is convincing proof that the palaeontological record is, and ever must be, a mere excerpt from the biological annals of the globe. III. THINNING OUT OF BEDS. Another cause by which the continuity of the palseontological record is affected is what is technically called the " thinning out " of beds. Owing to the mode in which sedimentary rocks are produced, IMPERFECTION OF PAL^EONTOLOGICAL RECORD. 67 it is certain that there 'must be for every bed a point whence the largest amount of sediment was derived, and in the neigh- bourhood of which the bed will therefore be thickest. Thus, if we take a series of beds, such as sandstones and conglo- merates, which are the product of littoral action, and are de- posited in shallow water near a coast-line, it will be found that these gradually decrease in thickness, or " thin out," as we pass away from the coast in the direction of deep water. On approaching deep water, however, we might find that, though the sandstones were rapidly dying out, the thickness of the entire series might still be preserved, owing to the commencement now of some deep-water deposit, such as lime- stone. The beds of limestone would at first be very thin, but in proceeding still in the direction of deeper water, we should find that they would gradually expand till they reached a point of maximum thickness, on the other side of which they would gradually thin out. Each individual bed, therefore, in any group of stratified rocks, may be regarded as an unequal mass, thickest in the centre, and gradually tapering off or " thinning out " in all directions towards the circumference (fig. 11). Fig. 11. Diagram to show the " thinning out" of beds, a, Sandstones and Conglomerates ; b, Limestones. In a general way this holds good, not only for any partic- ular bed, but for any particular aggregation or group of beds which we may choose to take. In the case, namely, of every group of beds, there must have been a particular point whither sediment was most abundantly conveyed, or where the other conditions of accumulation were especially favour- able. At this point, therefore, the beds are thickest, and from this they thin out in all directions. It need scarcely be pointed out, indeed, that some such state of things is un- avoidable in the case of every bed or group of beds, since no 68 INTRODUCTION. sea is boundless, and the sedimentary deposits of every ocean must come to an end somewhere. An excellent example of the phenomena above described may be derived from the Lower Carboniferous rocks of Bri- tain. Here we may start in South Wales and in Central England with the Carboniferous Limestone as a great calcare- ous mass over 1000 feet in thickness, and almost without a single intercalated layer of shale. Passing northwards, some of the beds of limestone begin to thin out, and their place is taken by strata of a different mineral nature, such as sand- stone, grit, or shale. The result of this is, that by the time we have followed the Carboniferous Limestone into York- shire and Westmorland, in place of a single great mass of limestone, we have an equivalent mass of alternating strata of limestone, sandstone, grit, and shale, with one or two thin seams of coal the limestones, however, still bearing a consi- derable proportion to the whole. Passing still further north- wards, the limestones go on thinning out, till in Central Scotland, in place of the dense calcareous accumulations of Derbyshire, the Lower Carboniferous series consists of a great group of sandstones, grits, and shales, with thick and work- able beds of coal, and with but few and comparatively insig- nificant beds of limestone. The state of things indicated by these phenomena is as follows : The sea in which the Lower Carboniferous rocks of Britain were deposited must have gradually deepened from north to south. The land and coast-line whence the coarser mechanical sediments were derived must have been placed somewhere to the north of Scotland, and the deepest part of the ocean must have been somewhere about Derbyshire. Here the conditions for lime-making were most favourable, and here consequently we find the greatest thickness of calcareous strata, and the smallest intermixture of mechanical deposits. The palaeontological results of this are readily deducible. The entire Lower Carboniferous series of Britain was prob- ably deposited in a single ocean, apparently destitute of land- barriers ; and consequently, taken as a whole, the fauna of this series may be regarded as one and indivisible. The con- ditions, nevertheless, which obtained in different parts of this IMPERFECTION OF PAL^EONTOLOGICAL RECORD. 69 area were very different ; and, as a necessary result, certain groups of animals flourished in certain localities, and were absent or but scantily represented in others. In the deeper parts of the area we have an abundance of Corals, with Crinoids, and at times Foraminifera. In the shallower parts of the area there is, on the other hand, a predominance of forms which affect water of no great depth. Still there is no difference in point of time between the deposits of differ- ent parts of the area ; and in order to obtain a true notion of the Lower Carboniferous fauna, we must add the fossils derived from one portion of the area to those derived from another. In many cases, however, we are acquainted with but one class of deposits belonging to a given period. We may have the deep-sea deposits of the period only, or we may know nothing but its littoral accumulations. In either case it is clear that there is an imperfection of the palaeontological record ; for we cannot have even a moderately complete re- cord of the marine animals alone of a particular period unless we have access to a complete series of the deposits laid down in the seas of that period. IV. DISAPPEARANCE OF FOSSILS. The last subject which need be mentioned in connection with the imperfection of the palseontological record is that of the disappearance of fossils from rocks originally fossiliferous. This, as a rule, is due to " metamorphism " that is to say, the subjection of the rock to a sufficient amount of heat to cause a rearrangement of its particles. When of at all a pronounced character, the result of metamorphism is invariably the obliteration of any fossils which might have been originally present in the rock. To this cause must be set down many great gaps in the palaeon- tological record, and the irreparable loss of much fossil evi- dence. The most striking example which is to be found of this is the great Laurentian series, which comprises some 30,000 feet of highly metamorphosed sediments, but which, with one not absolutely certain exception, has as yet yielded no remains of life, though there is strong evidence of the former existence in it of fossils. Another not uncommon cause of the disappearance of INTRODUCTION. organic remains from originally fossiliferous deposits is the percolation through them of water holding carbonic acid in solution. By this means fossils of a calcareous nature are dissolved out of the rock, and may leave no traces behind. This cause, however, can only operate to any extent in more or less loose and porous arenaceous deposits. Lastly, " cleavage " may be mentioned as a common cause of the disappearance of fossils. The cleavage, however, must be very intense, if it actually prevents the recognition of the deposit as one in which fossils formerly existed, though cases are not uncommon in which this occurs through thousands of feet of strata. As a more general rule, however, it is not very difficult to determine whether a cleaved rock has ever contained fossils or not, though it may be quite impossible to make out the exact nature and character of the organic remains. CHAPTEK V. CONCLUSIONS TO BE DRAWN FROM FOSSILS. WE have already seen that geologists have been led by the study of fossils to the all-important generalisation that the vast series of the Fossiliferous or Sedimentary rocks may be divided into a number of definite groups or " formations," each of which is characterised by its organic remains. It may simply be repeated here that these formations are not properly and strictly characterised by the occurrence in them of any one particular fossil. It may be that a formation con- tains some particular fossil, or fossils, not occurring out of that formation, and that in this way an observer may identify a given group with tolerable certainty. It "very often hap- pens, indeed, that some particular stratum, or sub-group of a series, contains peculiar fossils, by which its existence may be determined in various localities. As before remarked, however, the great formations are characterised properly by the association of certain fossils, by the predominance of certain families or orders, or by an assemblage of fossil re- mains representing the " life " of the period in which the formation was deposited. Fossils, then, enable us to determine the age of the deposits in which they occur. Fossils further enable us to come to very important conclusions as to the mode in which the fos- siliferous bed was deposited, and thus as to the condition of the particular district or region occupied by the fossiliferous bed at the time of the formation of the latter. If, in the 72 INTRODUCTION. first place, the bed contain the remains of animals such as now inhabit rivers, we know that it is " fluviatile " in its origin, and that it must at one time have either formed an actual river-bed, or been deposited by the overflowing of an ancient stream. Secondly, if the bed contain the remains of shell-fish, minute crustaceans, or fish, such as now inhabit lakes, we know that it is "lacustrine," and was deposited beneath the waters of a former lake. Thirdly, if the bed con- tain the remains of animals such as now people the ocean, we know that it is " marine " in its origin, and that it is a fragment of an old sea-bottom. We can, however, often determine the conditions under which a bed was deposited with greater accuracy than this. If, for example, the fossils are of kinds resembling the marine animals now inhabiting shallow waters, if they are accom- panied by the detached relics of terrestrial organisms, or if they are partially rolled and broken, we may conclude that the fossiliferous deposit was laid down in a shallow sea, in the immediate vicinity of a coast-line, or as an actual shore- deposit. If, again, the remains are those of animals such as now live in the deeper parts of the ocean, and there is a very sparing intermixture of extraneous fossils (such as the bones of birds or quadrupeds, or the remains of plants), we may presume that the deposit is one of deep water. In other cases, we may find, scattered through the rock, and still in their natural position, the valves of shells such as we know at the present day as living buried in the sand or mud of the sea-shore or of estuaries. In other cases, the bed may obviously have been an ancient coral-reef, or an accumula- tion of social shells, like Oysters. Lastly, if we find the deposit to contain the remains of marine shells, but that these are dwarfed of their fair proportions and distorted in figure, we may conclude that it was laid down in a brackish sea, such as the Baltic, in which the proper saltness was wanting, owing to its receiving an excessive supply of fresh water. In the preceding, we have been dealing simply with the remains of aquatic animals, and we have seen that certain CONCLUSIONS TO BE DKAWN FEOM FOSSILS. conclusions can be accurately reached by an examination of these. As regards the determination of the conditions of deposition from the remains of aerial and terrestrial animals, or from plants, there is not such an absolute certainty. The remains of land-animals would, of course, occur in " sub- aerial " deposits that is, in beds, like blown sand, accumu- lated upon the land. Most of the remains of land-animals, however, are found in deposits which have been laid down in water, and they owe their present position to having been drowned in rivers or lakes, or carried out to sea by streams. Birds, Flying Eeptiles, and Flying Mammals might also similarly find their way into aqueous deposits ; but it is to be remembered that many birds and mammals habitually spend a great part of their time in the water, and that these might therefore be naturally expected to present themselves as fossils in Sedimentary rocks. Plants, again, even when un- doubtedly such as must have grown on land, do not prove that the bed in which they occur was formed on land. Many of the remains of plants known to us are extraneous to the bed in which they are now found, having reached their present site by falling into lakes or rivers, or being- carried out to sea by floods or gales of wind. There are, however, many cases in which plants have undoubt- edly grown on the very spot where we now find them. Thus it is nOW eener mitted that the great coal- fields of the Carboniferous age are the result of the growth in situ of the plants which compose coal, and that these grew on vast marshy or partially submerged tracts of level Fig. 12. Erect Tree containing Reptilian a(J_ remains. Coal-measures, Nova Scotia. (After Dawson.) 74 INTRODUCTION. alluvial land. We have, moreover, distinct evidence of old land-surfaces, both in the Coal-measures and in other cases (as, for instance, in the well-known " dirt-bed " of the Pur- beck series). When, for example, we find the erect stumps of trees standing at right angles to the surrounding strata, we know that the surface through which these send their roots was at one time the surface of the dry land, or, in other words, was an ancient soil (fig. 12). CONCLUSIONS AS TO CLIMATE. In many cases fossils enable us to come to important conclusions as to the climate of the period in which they lived, but only a few instances of this can be here adduced. As fossils in the majority of instances are the remains of marine animals, it is mostly the temperature of the sea which can alone be determined in this way ; and it is important to remember that, owing to the existence of heated currents, the marine climate of a given area does not necessarily imply a correspondingly warm climate in the neighbouring land. Land-climates can only be determined by the remains of land-animals or land-plants, and these are comparatively rare as fossils. It is also im- portant to remember that all conclusions on this head are really based upon the present distribution of animal and vegetable life on the globe, and are therefore liable to be vitiated by the following considerations : a. Most fossils are extinct, and it is not certain that the habits and requirements of any extinct animal were exactly similar to, or even at all resembling, those of its nearest living relative. &. When we get very far back in time, we meet with groups of organisms so unlike anything we know at the present day as to render all conjectures as to climate found- ed upon their supposed habits more or less uncertain and unsafe. c. In the case of marine animals, we are as yet very far from knowing the exact limits of distribution of many species within our present seas ; so that conclusions drawn from living forms as to extinct species are apt to prove incorrect. For instance, it has recently been shown that many shells CONCLUSIONS TO BE DRAWN FROM FOSSILS. 75 formerly believed to be confined to the Arctic Seas have, by reason of the extension of Polar currents, a wide range to the south ; and this has thrown doubt upon the conclusions drawn from fossil shells as to the Arctic conditions under which certain beds were supposed to have been deposited. d. The distribution of animals at the present day is certainly dependent upon other conditions beside climate alone ; and the causes which now limit the range of given animals are certainly such as belong to the existing order of things. But the establishment of the present order of things does not date back in many cases to the introduction of the present species of animals. Even in the case, therefore, of existing species of animals, it can often be shown that the past distribution of the species was different formerly to what it is now, not necessarily because the climate has changed, but because of the alteration of other conditions essential to the life of the species or conducing to its ex- tension. Still, we are in many cases able to draw completely reliable conclusions as to the climate of a given geological period, by an examination of the fossils belonging to the period. Among the more striking examples of how the past climate of a region may be deduced from the study of the organic remains contained in its rocks, the following may be mentioned : It has been shown that in Eocene times, or at the commencement of the Tertiary period, the climate of what is now Western Europe was of a tropical or sub- tropical character. Thus the Eocene beds are found to contain the remains of shells such as now inhabit tropical seas, as, for example, Cowries and Volutes ; and with these are the fruits of palms, and the remains of other tropical plants. It has been shown, again, that in Miocene times, or about the middle of the Tertiary period, Central Europe was peopled with a luxuriant flora resembling that of the warmer parts of the United States, and leading to the con- clusion that the mean annual temperature must have been at least 30 hotter than it is at present. It has been shown that, at the same time, Greenland, now buried beneath a vast V6 INTRODUCTION. ice-shroud, was warm enough to support a large number of trees, shrubs, and other plants, such as inhabit the temperate regions of the globe. Lastly, it has been shown, upon physi- cal as well as paleeontological evidence, that the greater part of the North Temperate Zone, at a comparatively recent geological period, has been visited with all the rigours of an Arctic climate, resembling that of Greenland at the present day. This is indicated by the occurrence of Arctic shells in the superficial deposits of this period, whilst the Musk-ox and the Eeindeer roamed far south of their present limits. CHAPTER VI. DIVISIONS OF THE ANIMAL KINGDOM AND SUCCESSION OF ORGANIC TYPES. IT seems hardly necessary to remark that Palaeontology, as a science, is based upon the kindred sciences of Zoology and Botany, and that no satisfactory acquaintance with the former can be arrived at without the previous acquisition of some knowledge of the latter. It cannot be pretended to teach here even the rudiments of these sciences, but there are a few points which may be noticed as having a special bearing upon the study of Palaeontology. CLASSIFICATION OF THE ANIMAL KINGDOM. Leaving the vegetable kingdom till we come to speak of fossil plants, a few remarks may be made on the classification of the animal kingdom. Vast as is the number of known animals, all, whether living or extinct, may be classed under some five or six primary divisions or "morphological types," which are technically spoken of as the " sub-kingdoms." All the animals in any one sub-kingdom agree with one another in their structural type, or in the fundamental plan upon which they are constructed ; and they differ from one another simply in the modifications of this common plan. No com- parison, therefore, is possible between an animal belonging to one sub-kingdom, and one belonging to another, since their distinguishing characters are the result of the modifica- tion of two essentially different ground-plans. Hence it is possible to arrange the animals of any one sub-kingdom in something like a linear series, in which the lowest of the INTRODUCTION. series most closely approaches the primitive or ideal form of the sub-kingdom, whilst the highest exhibits the greatest amount of complexity and specialisation of this type. But it is not possible to establish any such linear classification for the animal kingdom as a whole. Given an animal of a lower " sub-kingdom " than another animal, no amount of complexity, no specialisation of organisation, can raise the former above the latter. The one may be the result of the high evolution of a low morphological type, the other may be the result of the low evolution of a higher morphological type, but the superiority of the ground-plan gives the latter the higher place. We must therefore abandon the idea that it is possible to establish a linear classification of the animal kingdom. The terms "class," "order," "genus," "sub-genus," "species," and "variety," are employed by the palaeontologist in pre- cisely the same sense, and with precisely the same limita- tions, as by the zoologist. We must notice, however, that a palceontological " species " has not always or necessarily the same value as that which a zoological species ought invariably to possess. This arises from the fact that the determination of fossil species is, almost without exception, based solely upon the characters of the hard parts of the animal these, also, being often but imperfectly preserved. A fossil species, therefore, cannot, from the nature of things, be as thoroughly defined as a living one ; and it is both possible and prob- able that variations in the form of the skeleton, especially if an integumentary one, may often depend upon mere in- dividual, sexual, or local peculiarities, which could be at once discovered in the case of living forms, but which can hardly be detected as regards extinct types. Moreover, there is a practical inconvenience attending the use of the terms " variety " and " sub-genus " in palaeontology, which is not found in zoology, owing to the very different nature of the working material of these two sciences. Many palaeon- tologists, therefore, prefer, as we think rightly, to follow the general practice of giving distinct names to " varieties " and " sub-genera," thus practically raising them to the rank of " species " and " genera ; " and this practice can hardly be in- CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 79 jurious if accompanied with the well-understood reservation that this is done as a matter of convenience only, and that a somewhat wider and looser signification is to be given to the terms " species " and " genera " in palaeontology than would be admissible in zoology. At the same time, this practice may be, and has been, carried too far; and in the case of very variable or " protean " species, it is certainly advisable to adhere to the plan usually adopted by British palaeontolo- gists namely, to define the species by its central type, and to group the variable forms under this type as varieties. The duration in time, or " vertical range," of fossil species varies greatly in different cases. Some species have an extraordinarily extended range, sometimes passing through two or three entire formations, and in such cases they generally exhibit numerous varieties. Others, again, are singularly restricted, and do not pass beyond the limits of a single subdivision of a formation, or sometimes even a single bed. In any case, when a species has once fairly died out, it never reappears again. As a general rule, it is the animals which have the lowest and simplest organisation that have the longest range in time, and the additional pos- session of microscopic or minute dimensions seems also to favour longevity. Thus some of the Foraminifexa appear to have survived, with little or no perceptible alteration, from the Silurian period to the present day ; whereas large and highly -organised animals, though long-lived as individuals, rarely seem to live long specifically, and have, therefore, usually a restricted vertical range. Some genera, as some species, are short - lived ; whereas others extend through a succession of zoological periods with extraordinarily little modification. Among these "persistent types" may be specially mentioned the genus Lingula among the Brachio- poda, and Nautilus among the Cephalopoda, of which the former commenced in the Cambrian and the latter in the Silurian, and both of which are represented by living species. While the great majority' of fossils are extinct, and while many of them are extremely unlike any existing forms, my fossil animal has hitherto been detected which cannot (pe referred to one or other of the existing sub-kingdoms. No 8Q INTRODUCTION. fossil animals, indeed, possess peculiarities so great as to entitle them to be placed in any class, other than in one of the classes of recent forms. On the other hand, the differ- ences between some of the ancient types of life and the existing ones are so great, that palaeontologists have been compelled to construct new sub-classes, orders, and genera for their reception. Moreover, many fossil animals are not only very different from living ones, but they are often " compre- hensive " or " transitional " in their characters. In other words, fossil animals are often " comprehensive types," and combine in themselves characters now only found separ- ate, thus serving as " transitional links " between groups which are at present widely removed from one another. For example, the reptiles and the birds form at the present day two widely separated classes, but some fossil birds exhibit peculiarities of a distinctly reptilian character, and some fossil reptiles approximate to the birds in structure ; and the fossil forms thus partially fill up the gap w T hich now exists between these two great divisions of the animal kingdom. Again, many fossil animals exhibit what are termed " generalised " characters. If, namely, we construct for our- selves a " general " or " ideal " type for any great group of animals a type which shall possess all the essential char- acters of the group, without its non-essential ones then we find that the fossil animals of the same group are generally nearer to this type than are its living representatives. Moreover, the older representatives of any given group are usually nearer to the ideal type of the group or are more "generalised" than are the later representatives of the same group. All zoologists, however, admit that the process of development in any individual animal is one in which there is a gradual progress from the general to the special, the embryo being nearer to the general type of the group to which it belongs than the adult is. In other words, the embryo animal is more generalised than the adult, and the process of development is one of specialisation. Admitting this, it follows that the fossil forms belonging to any given group, in so far as they are " generalised " in their characters, CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 81 may fairly be said to be " embryonic " types ; and as the oldest forms of any given group are usually the least specialised, so they are likewise the most " embryonic.", It must be borne in mind, however, that if we speak of fossil animals as being " embryonic types," we can only do so on the distinct under- standing that it is not thereby implied that they were in any way degraded forms, or that they were at all less perfectly constructed or less thoroughly adapted for their surroundings than their modern representatives. The following synoptical table gives briefly the leading divisions of the animal kingdom, and the chief characters of these : TABULAR VIEW OF THE CHIEF DIVISIONS OF THE ANIMAL KINGDOM. INVERTEBRATE ANIMALS. SUB-KINGDOM I. PROTOZOA. Animal simple or forming colonies, usually very minute ; the body composed of the structureless, jelly-like, albuminous substance called "sarcode;" not divided into regular segments; having no nervous system ; no regular circulatory system ; usually no mouth ; no definite body-cavity or digestive system, or at most but a short guHet. CLASS A. GREGARINID^. Minute Protozoa which inhabit the interior of insects and other animals, and which have not the power of throwing out prolongations of their substance (pseudopodia). No mouth. CLASS B. RHIZOPODA (Root-footed Protozoa). Protozoa which are simple or compound, and have the power of throwing out and retracting prolongations of the body-substance (the so-called " pseudopodia "). No mouth, in most, if not in all. Order 1. Monera. Ex. Protogenes. Order 2. Amcebea. Ex. Proteus Animalcule (Amreba). Order 3. Foraminifera. Ex. Lagena, Nodosaria, Globigerina. Order 4.. Radiolaria.Ex. Thalassicolla, Polycystina. Order 5. Spongida. Ex. Fresh-water Sponge (Spongilla), Venus's Flower-basket (Euplectella). CLASS C. INFUSORIA (Infusorian Animalcules). Protozoa with a mouth and short gullet ; destitute of the power of emitting pseudopodia ; fur- nished with vibratile cilia or contractile filaments ; the body usually composed of three distinct layers. Order 1. Ciliata. Ex. Bell-animalcule (Vorticella), Paramcecium. Order 2. Flagellata. Ex. Peranema. Order 3. Suctoria. Ex. Podophrya. VOL. I. F 82 INTRODUCTION. SUB-KINGDOM ILCCELENTERA TA. Animals whose alimentary canal communicates freely with the general cavity of the body ; body composed essentially of two layers or mem- branes, an outer layer or " ectoderm," and an inner layer or " endoderm." No circulatory system or heart, and in most no nervous system. Skin furnished with minute stinging organs or "thread-cells." Distinct re- productive organs in all. CLASS A. HYDROZOA. Walls of the digestive sac not separated from those of the general body-cavity, the two coinciding with one another. Reproductive organs external. Sub-class I. HYDROIDA (Hydroid Zoophytes). Order 1. Hydrida. Ex. Fresh-water Polype (Hydra). Order 2. Corynida. Ex. Pipe-coralline (Tubularia). Order 3. Sertularida.Ex. Sea-firs (Sertularia). Sub-class II. SIPHONOPHORA (Oceanic Hydrozoa). Order 4. Calycophoridce. Ex. Diphyes. Order 5. Physophoridce. Ex. Portuguese Man-of-war (Physalia). Sub-class III. DISCOPHORA (Jelly-fish). Order 6. Medusidce. Ex. Trachynema. Sub-class IV. LUCERNARIDA (Sea-blubbers). Order 7. Lucernaridce. Ex. Lucernaria. Order 8. Pelagidce. Ex. Pelagia. Order 9. Rhizostomidce. Ex. Rhizostoma. Sub-class V. GRAPTOLITID.E (extinct). Sub-class VI. HYDROCORALLIN^E. Ex. Millepora, Stylaster. CLASS B. ACTINOZOA. Stomach opening below into the body-cavity? which is divided into a number of compartments by a series of vertical partitions or " mesenteries." Reproductive organs internal. Order 1. Zoantharia. Tentacles simply rounded, in multiples of five or six. Ex. Sea-anemones (Actinidse), Star- corals (Astrseidse), Brain-corals (Meandrina), Madre- pores (Madreporidse). Order 2. Alcyonaria. Tentacles fringed, in multiples of four. Ex. Dead-man's-toes (Alcyonium), Organ-pipe Coral (Tubipora), Sea-rods (Virgularia), Sea-pens (Penna- tula), Red Coral (Corallinm), Heliopora, Heliolites. Order 3. Rugosa (extinct). Order 4. Ctenophora. Animal oceanic, swimming by means of bands of cilia or " ctenophores." Ex. Pleurobrachia, . Venus's Girdle (Cestum). S UB-KINGDOM III. A NX UL 01 DA . Animals in which the alimentary canal is completely shut off from the general cavity of the body, and in which there is a distinct nervous system. A true blood-circulatory system may or may not be present. In all there is a peculiar system of canals, which usually communicate CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 83 with the exterior, and which constitute what is called the " water- vascular system." The body of the adult is never composed of a succession of definite rings, or provided with successive pairs of appendages disposed symmetrically on the two sides of the body. The Annuloida are divided into two great classes : A. ECHINODERMATA. Integument composed of numerous calcareous plates joined together, or leathery and having grains, spines, or tubercles of calcareous matter developed in it. Water- vascular system (ambulacral system) mostly employed in locomotion, and generally communicating with the exterior. Adult generally more or less star-like or " radiate " in shape ; young mostly showing more or less complete " bilateral sym- metry," that is, showing similar parts on the two sides of the body. Nervous system radiate. Order 1. Crinoidea (Sea-lilies). Ex. Feather-star (Comatula), Me- dusa-head Crinoid (Pentacrinus), Stone-lily (En- crinus). Order 2. Blastoidea (extinct). Order 3. Cystoidea (extinct). Order 4. Ophiuroidea (Brittle-stars). Ex. Sand-stars (Ophiura), Brittle-stars (Ophiocoma). Order 5. Asteroidea (Star-fishes). Ex. Cross-fish (Uraster), Sun- star (Solaster), Cushion-star (Goniaster). Order 6. Echinoidea (Sea-urchins). Ex. Sea -eggs (Echinus), Heart-urchins (Spatangus). Order 7. Holothuroidea (Sea-cucumbers). Ex. Trepangs (Holo- thuria). B. SCOLECIDA. Body usually flattened, or cylindrical and worm-like ; integument soft, without lime. Water-vascular system not assisting in locomotion. Nervous system consisting of one or two ganglia or little masses, and not disposed in a radiate manner. Order 1. Tceniada. Ex. Tape-worm (Tsenia). Order2. Trematoda (Suctorial worms). Ex. Liver-fluke (Dis- toma). Order 3. Turbellaria. Ex. Planarians (Planaria), Ribbon-worms (Nemertes). Order 4. Acanthocephala (Thorn -headed worms). Ex. Echino- rhynchus. Order 5. Gordiacea (Hair-worms). Ex. Gordius. Order 6. Nematoda (Thread-worms). Ex. Round-worm (Ascaris), Guinea-worm (Filaria), Vinegar-eel (Anguillula). Order 7. Rotifera (Wheel-animalcules). Ex. Builder -animalcule (Melicerta), Flexible Creeper (Notommata). SUB-KINGDOM I V.A NNULOSA . Animal composed of numerous definite segments or " somites;" arranged longitudinally, one behind the other. Nervous system always present, consisting typically of a double chain of nervous masses, or ganglia, INTRODUCTION. which are placed along the lower surface of the body, and form a collar around the gullet. Limbs (when present) turned toward that side of the body on which the main masses of the nervous system are situated. DIVISION A. ANARTHROPODA. Locomotive appendages, when pres- ent, not distinctly jointed or articulated to the body. CLASS I. GEPHYREA. Ex. Spoon-worms (Sipunculus). CLASS II. ANNELIDA (Ringed-worms). Order 1. Hirudinea. Ex. Leeches (Sanguisuga, Hirudo). Order 2. Oligochceta. Ex. Earth-worms (Lumbricus), Water- worms (Nais). Order 3. Tubicola. Ex. Tube- worms (Serpula). Order 4. Errantia. Ex. Sand-worms and Sea-centipedes (Nereis) , Lob-worm (Arenicola), Sea-mouse (Aphrodite). CLASS III. CH^TOGNATHA (Arrow-worms). Ex. Sagitta. /- DIVISION B. ARTHROPODA. Locomotive appendages jointed or articu- lated to the body. CLASS I. CRUSTACEA. Respiration aquatic, mostly by gills. Two pairs of antennae. Limbs more than four pairs in number, carried upon the thorax, and generally upon the abdomen also. Order 1. Ichthyophthira. Ex. Lernaea. Order 2. Rhizocephala. Ex. Peltogaster. Order 3. Cirripedia. Ex. Barnacles (Lepas), Acorn-shells (Bal- anus). Order 4. Ostracoda. Ex. "Water-fleas (Cypris). Order 5. Copepoda. Ex. Cyclops. Order 6. Cladocera. Ex. Branched-horned Water-fleas (Daphnia). Order 7. Phyllopoda. Ex. Brine-shrimp (Artemia). Order 8. Trilobita (Extinct). Order 9. Merostomata. Ex. King-crabs (Limulus). Order 10. Lcemodipoda. Ex. Whale-louse (Cyamus). Order 11. Isopoda. Ex. Wood-lice (Oniscus), Slaters (Ligia). Order 12. Amphipoda. Ex. Sandhopper (Talitrus), Fresh-water Shrimp (Gammarus). Order 13. Stomapoda. Ex. Locust-shrimp (Squilla). Order 14. Decapoda. Ex. Lobster (Homanis), Cray-fish (Astacus), Shrimps (Crangon) ; Hermit-crabs (Pagurus) ; Crabs (Cancer, Carcinus), Land-crabs (Gecarcinus). CLASS II. ARACHNID A. Respiration aerial, by pulmonary chambers or air-tubes (tracheae) in the higher forms. Antennae converted into jaws. Head and thorax amalgamated. Four pairs of legs. Abdomen without limbs. Order 1. Podpsomata (Sea-spiders). Ex. Pycnogonum. Order 2. Monomerosomata. Ex. Mites (Acarus), Water - mites (Hydrachna), Ticks (Ixodes). OrderS. Adelarthrosomata. Ex. Harvest - spiders (Phalangidae), Book-scorpions (Chelifer). Order 4. Pedipalpi.Ex. Scorpions (Scorpio). CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 85 Order 5. Araneida. Ex. House-spiders (Tegenaria), Field-spiders (Epeira). CLASS III. MYRIAPODA. Respiration aerial, by tracheae (air-tubes) or by the skin. Head distinct ; remainder of body composed of nearly similar segments. Legs more than eight pairs in number, and borne partly upon the abdomen. One pair of antennae. Order 1. Ghilopoda. Ex. Centipedes (Scolopendra). Order 2. Chilognatha. Ex. Millipedes (lulus). Order 3. Pauropoda. Ex. Pauropus. Order 4. Onychophora. Ex. Peripatus. CLASS IV. INSECTA. Respiration aerial, by tracheae. Head, thorax, and abdomen distinct. One pair of antennae. Three pairs of legs, and generally two pairs of wings on the thorax. No locomotive limbs on the abdomen. Order 1. Anoplura. Ex. Lice (Pediculus). Order 2. Mallophaga (Bird-lice). Order 3. Colkmbola.Ex. Podura. Order 4. Thysanura. Ex. Lepisma. Order 5. Hemiptera. Ex. Plant-lice (Aphides), Field-bug (Pen- tatoma), Cochineal Insects (Coccus). Order 6. Orthoptera. Ex. Locusts (Acrydium), Grasshoppers (Gryllus), Crickets (Acheta), Cockroach (Blatta). Order 7. Neuroptera. Ex. White Ants (Termes), Dragon-flies (Libellulidse), May-flies (Ephemeridse). Order 8. Aphaniptera. Ex. Fleas (Pulex). Order 9. Diptera. Ex. Gnats (Culex), Crane-flies (Tipula), House- flies and Flesh-flies (Musca). Order 10. Lepidoptera (Butterflies and Moths). Order 11. Hymenoptera. Ex. Bees (Apidae), Humble-bees (Bom- bidae), Wasps (Vespidae), Ants (Formicidae), Saw- flies (Tenthredinidae). Order 12. Strepsiptera. Ex. Sty lops. Order 13. Coleoptera (Beetles). SUB-KINGDOM V.MOLL USCA . Animal soft-bodied, generally with a hard covering or shell. Nervous system consisting of a single ganglion or of scattered pairs of ganglia. A distinct heart and breathing-organ, or neither. The Mollusca may be divided into the two following primary divisions, containing the following classes : A. MOLLUSCOIDA. Nervous system consisting of a single ganglion or of a principal pair of ganglia. No heart, or an imperfect one. CLASS I. POLYZOA. Animal always forming compound growths or colonies. No heart. The mouth of each zooid surrounded by a circle or crescent of ciliated tentacles. Ex. Sea- mats (Flustra), Lace-coral (Fenestella). 86 INTRODUCTION. / CLASS II. TUNICATA. Animal simple or compound, enclosed in a leathery or gristly case. An imperfect heart. Ex. Sea- squirts (Ascidia). CLASS III. BRACHIOPODA. Animal always simple ; the body enclosed in a bivalve shell. Mouth furnished with two long fringed processes or "arms." Ex. Lamp-shells (Tere- bratula). B. MOLLUSCA PROPER. Nervous system consisting of three principal pairs of ganglia. Heart well developed, consisting of at least two chambers. CLASS IV. LAMELLIBRANCHIATA (Bivalve Shell-fish). No distinct head ; no teeth. Body enclosed in a shell which is " bi- valve," or composed of two distinct pieces. One or two leaf-like gills on each side of the body. Ex. Oyster (Ostrea), Scallop (Pecten), Mussel (Mytilus). CLASS V. GASTEROPODA. A distinct head and toothed tongue. Shell absent in some, but mostly present, and usually consisting of a single piece ("univalve"). Locomotion effected by creeping about on the flattened under-surface of the body (" foot "), or by swimming by means of a fin-like modifi- cation of the same. Ex. Whelks (Buccinum), Limpets (Patella), Sea-lemons (Doris), Land-snails (Helix), Slugs (Limax). CLASS VI. PTEROPODA. Animal oceanic, swimming by means of two wing-like appendages, one on each side of the head. Size minute. Ex. Cleodora. CLASS VII. CEPHALOPODA. Animal with eight or more arms, placed in a circle round the mouth. Mouth armed with jaws', and a toothed tongufc. Two or four plume-like gills-. In front of the body, a muscular tube (" funnel ") through which is expelled the water which has been used in respiration. An external shell in some, an internal skeleton in others. Ex. Calamaries .(Loligo), Cuttle- fishes or Poulpes (Octopus), Paper-Nautilus (Argonauta), Pearly Nautilus (Nautilus). VERTEBRATE ANIMALS. SUB-KINGDOM VI. VERTEBRA TA. Body composed of a number of definite segments arranged longitudi- nally, or one behind the other. The main masses of the nervous system are placed on the dorsal aspect of the body, and are completely shut off from the general body-cavity. The limbs (when present) are turned away from that side of the body on which the main nervous masses are situated, and are never more than four in number. In most cases a back- bone, or " vertebral column," is present in the fully-grown animal. CLASS I. PISCES (Fishes). Breathing- organs in the form of gills. CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 87 Heart usually of two chambers, rarely of three. Blood cold. Limbs, when present, converted into fins. Order 1. Pharyngobranchii. Ex. Lancelet (Amphioxus). Order 2. Marsipobranchii. Ex. Lamprey (Petromyzon), Hag-fish (Myxine). OrderS. Teleostei (Bony Fishes). Ex. Eels (Muramidee), Her- rings (ClupeidaB), Salmon and Trout (Salmonidae), Cod and Haddock (Gadidse), Flat-fishes (Pleuronec- tidse), Perch (Percidse), Mackerel (Scomberidse). Order 4. Ganoidei. Ex. Bony Pike (Lepidosteus), Paddle-fish (Spatularia), Sturgeon (Sturio). Order 5. Elasmobranchii. Ex. Sharks (Carcharidse), Dog-fishes (Scylliadse), Saw-fishes (Pristis), Kays and Skates (Raiidse). Order 6. Dipnoi. Ex. Mud-fish (Lepidosiren), Ceratodus. CLASS II. AMPHIBIA (Amphibians). Breathing-organs in the young in the form of gills alone, afterwards lungs, either alone or associated with gills. Skull joined to the backbone by two articulating surfaces (" cori- clyles"). Limbs never converted into fins. Heart in the young of two chambers only, in the adult of three chambers. Blood cold. Order 1. Labyrinthodontia (extinct). Order 2. Ophiomorpha. Ex. Csecilia. Order 3. Urodela (Tailed Amphibians). Ex. Water-newts (Tri- ton), Salamanders (Salarnandra), Axolotl (Siredon), Mud-eel (Siren). Order 4. Anoura (Tailless Amphibians). Ex. Frogs (Rana), Tree- frogs (Hyla), Toads (Bufo), Surinam toads (Pipa). CLASS III. REPTILIA (Reptiles). Respiratory organs in the form of lungs, never in the form of gills. Heart three-chambered, rarely four- chambered, the pulmonary and systemic circulations always connected together directly, either in the heart itself or in its immediate neighbour- hood. Blood cold. Skull jointed to the backbone by a single articulat- ing surface or " condyle." Each half of the lower jaw composed of seve- ral pieces. Appendages of the skin in the form of scales or plates. Order 1. Ohelonia. Ex. Turtles (Cheloniidae), Soft Tortoises (Trionycidse), Terrapins (Emydidse), Land Tortoises (Testudinidse). Order 2. Ophidia. Ex. Vipers (Viperidse), Rattlesnakes (Crota- lidae), Sea-snakes (Hydrophidse), Boas and Pythons OrderS. Lacertilia. Ex. Lizards (Lacerta), Iguanas (Iguanidae), Monitors (Varanidae), Chameleons (Chamaeleontidse). Order 4. Crocodilia. Ex. Crocodiles, Alligators, Gavials. Order 5. Ichthyopterygia (extinct). Ex. Ichthyosaurus. Order 6. Sauropterygia (extinct). Ex. Plesiosaurus. Order 7. Pterosauria (extinct). Ex. Pterodactylus, Pteianodon. Order 8. Anomodontia (extinct). Ex. Dicynodon. INTRODUCTION. Order 9. Deinosauria (extinct). Ex. Iguanodon. Order 10. Theriodontia (extinct). Ex. Cynodraco. CLASS IV. AVES (Birds). Respiratory organs in the form of lungs, never in the form of gills. Lungs connected with air-receptacles placed in different parts of the body. Heart four-chambered. Blood warm. Skull connected with the backbone by a single articulating surface or " condyle." Each half of the lower jaw composed of several pieces. Ap- pendages of the skin in the form of feathers. Cavities of the chest and abdomen not separated by a complete partition (diaphragm). Fore-limbs converted into wings. Animal oviparous. A. Sub-class RATIT.E. Order 3. Cursores (Runners). Ex. Ostrich (Struthio), American Ostrich (Rhea), Emeu (Dromaius), Cassowary (Casu- arius), Apteryx, Dinornis. B. Sub-class CARINAT.E. Order 1. Natatores (Swimmers). Ex. Penguins (Spheniscidae), Gulls (Laridae), Ducks (Anatidae), Geese (Anserinse), Flamingos (Phaenicopteridae). 4 Order 2. Grallatores (Waders). JEsc. Rails (Rallidse), Water-hens (Gallinulae), Cranes (Gruidae), Herons (Ardeidae), Storks (Ciconinae), Snipes and Woodcock (Scolop- acidae), Plovers, Oyster - catchers, and Turnstones (Charadriidae). Order 3. Rasores (Scratchers). Ex. Grouse, Ptarmigan, Partridges, Pheasants, Turkey, Guinea-fowl, Domestic Fowl, Pea -fowl (Gallinacei) ; Doves, Pigeons, Ground- pigeons (Columbacei). Order 4. Scansores (Climbers). Ex. Cuckoos (Cuculidse), Wood- peckers (Picidae), Parrots, Cockatoos, Parrakeets (Psittacidae), Toucans (Rhamphastidae), Trogons (Trogonidae). Order 5. Insessores (Perchers). Ex. Crows, Magpies, and Jays (Corvidae), Starlings (Sturnidae), Finches, Grosbeaks, Larks (Fringillidae), Thrushes, Blackbirds, Orioles (Merulidae), Creepers and Wrens (Certhidse), Hum- ming-birds (Trochilidae), Swallows and Martins (Hirundinidae), Swifts (Cypselidae), King - fishers (Alcedinidse). Order 6. Raptores (Birds of Prey). Ex. Owls (Strigidse), Falcons and Hawks (Falconidae), Eagles (Aquilina) Vultures (Vulturidae), American Vultures (Cathartidae), Sec- retary-bird (Gypogeranus). C. Sub-class SAURORNITHES. Order Saururce (extinct). Archaeopteryx. D. Sub-class ODONTORNITHES. Order 1. Odontolcce (extinct). Hesperornis. Order 2. Odontotormce (extinct). Ichthyornis, Apatornis. CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 89 CLASS V. MAMMALIA (Mammals or Quadrupeds). Respiratory organs in the form of lungs, which are never connected with air-sacs placed in different parts of the body. Heart four-chambered. Blood warm. Skull united to the backbone by two articulating surfaces or " condyles." Each half of the lower jaw composed of a single piece. Appendages of the skin in the form of hairs. Young nourished by means of a special fluid the milk, secreted by special glands the mammary glands. Animal vivi- parous. A. NON-PLACENTAL MAMMALS. The young not provided with a placenta. Order 1. Monotremata. Ex. Duck-mole (Ornithorhynchus), Spiny Ant-eater (Echidna). Order 2. Marsupialia. Ex. Kangaroos (Macropodidee), Kangaroo- bear (Phascolarctos), Phalangers (Phalangistidse), Op- ossums (Didelphidae), Tasmanian Devil (Dasyurus). B. PLACEXTAL MAMMALS. The young provided with a placenta. Order 3. Edentata. Ex. Sloths (Brady podidae), Armadillos (Dasy- podidae), Hairy Ant-eaters (Myrmecophagidae), Scaly Ant-eaters (Manis). Order 4. Sirenia. Ex. Manatee (Manatus), Dugong (Halicore). Order 5. Cetacea. Ex. Whalebone-whales (Balaenidae), Sperm- whales (Physeteridae), Dolphins and Porpoises (Del- phinidae). Order 6. Ungulata (Hoofed Quadrupeds). Ex. Rhinoceros ; Tapir; Horse, Ass, and Zebra (Equidae) ; Hippopotamus ; Hogs and Peccaries (Suida) ; Camels and Llamas (Camelidae) ; Giraffe ; Stags, Elk, Reindeer (Cer- vidse) ; Antelopes (Antilopidse) ; Sheep and Goats (Ovidse) ; Oxen and Buffaloes (Bovidae). Order 7. Dinocerata (extinct). Ex. Dinoceras. Order 8. Tillodontia (extinct). Ex. Tillotherium. Order 9. Toxodontia (extinct). Ex. Toxodon. Order 10. Hyracoidea. Ex. Hyrax. Order 11. Proboscidea. Ex. Elephants (Elephas). Order 12. Carnivora. Ex. Seals (Phocidae), Bears (Ursidae), Ra- coons (Procyon), Badgers (Melidae), Weasels and Otters (Mustelidae), Civets and Genettes (Viver- ridae), Dogs, Wolves, and Foxes (Canidae) ; Hyaenas (Hyaenidae), Cats, Lynxes, Leopards, Tigers, Lions (Felidse). Order 13. Rodentia. Ex. Hares and Rabbits (Leporidae), Porcu- pines (Hystricidae), Beavers (Castoridae), Mice and Rats (Muridae), Dormice (Myoxidae), Squirrels and Marmots (Sciuridae). Order 14. Cheiroptera. Ex. Common Bats (Vespertilionidae), Horseshoe-bats (Rhinolophidae), Vampire-bats (Phyl- lostomidae), Fox-bats (Pteropidae). 90 INTRODUCTION. Order 15. Insectivora Ex. Moles (Talpidse), Shrew-mice (Sori- cidae), Hedgehogs (Erinaceidae). Order 16. Quadrumana. Ex. Aye-aye (Cheiromys), Lemurs (Le- muridae), Spider-monkeys (Ateles), Howlers (My- cetes), Macaques (Macacus), Baboons (Cynocephalus), Gibbons (Hylobates), Orang (Simia), Gorilla and Chimpanzee (Troglodytes). Order 17. Bimana. Man (Homo Sapiens). GENERAL SUCCESSION AND PROGRESSION OF ORGANIC TYPES. Whilst admitting the impossibility of arranging the animal kingdom upon any linear plan, no doubt obtains as to the fact that some of the fundamental " morphological types," or plans upon which animals have been constructed, are higher than others. Every one admits, for example, that the Ver- tebrate type is higher than the Molluscan or the Articulate type, an admission which is not affected by the fact that the highest Molluscs and Articulates are superior in point of organisation to the lowest Vertebrates. In the same way, within the limits of each sub-kingdom, every one admits that some of the groups are higher than others. Every one, for example, would admit that a Mammal is a superior animal to a Fish. It follows from this that a certain general arrangement of the animal kingdom, as a whole, is possible, upon the comparative basis of the morphological type of the sub-kingdoms. Similarly a general and more exact arrangement of the classes and orders of each sub- kingdom may be made by the degree of perfection in which the type of the sub-kingdom is carried out in each. No generalisation of Palaeontology seems to stand on a firmer basis than that which asserts that there has been a general succession of organic types, and that the appearance of the lower forms of life has in the main preceded that of the higher forms in point of time. In other words, it is one of the generalisations of Palaeontology that there has not only been a succession, but also a progression, of organic types in proceeding from the earliest fossiliferous deposits up to the present day. Whilst this general law remains, as we believe, unassailable, there are some important considerations which must not be lost sight of. In the first place, it is GENERAL SUCCESSION OF ORGANIC TYPES. 91 very doubtful if we are as yet acquainted with the absolute time of the first appearance upon the globe of even one of the sub-kingdoms. Future discoveries, therefore, are almost certain to push back still further into the remote vistas of the past the point of time at which each morphological type first made its appearance upon the globe. Still, there is little likelihood that the relative times of appearance of the great groups, as compared with one another, will be affected by the researches of the future. It remains almost certain that we shall find that the lower types were followed in point of time by the higher. In the second place, we find all the primary types in existence before the close of the Silurian period; and he would be rash indeed who would dogmatically deny that they might all have been present in the earlier Cambrian period. This, at first sight, might seem almost to negative the above generalisation, but it does not affect its value if fairly examined. The lower sub-kingdoms of #ie Inverte- brate animals appeared so early that their origin is lost in the mists of antiquity, and we can say nothing positively as to the time when each came into existence. The Cambrian deposits are underlaid by the vast series of the Laurentian deposits, representing an incalculable lapse of time. These ancient sediments, with one exception, have hitherto proved barren of life, owing to the intense metamorphism to which they have been subjected, and they consequently yield no evidence bearing on the question in hand. They serve to show us, however, by their presence alone, that we must in the meanwhile leave the Invertebrate sub-kingdoms out of account altogether as bearing upon the question of the succession and progression of organic types. We do not know when these sub-kingdoms commenced, and hence we have no right to assert either that they were all introduced simul- taneously, or that they came into being successively. We may be sure, however, of one thing they did not commence at the points where now we find their earliest traces. There remains, then, only the sub-kingdom of the Vertebrate animals which can reasonably be appealed to as evidence on this question. The stratified series is long enough to render it 92 INTRODUCTION. certain that it contains traces of the first appearance of, at any rate, the higher classes of these, though we doubt- less are ignorant of the absolute moment at which each appeared. If, therefore, it can be shown that there has been a progression as far as this sub - kingdom is con- cerned, then there would, by analogy, be the greatest pro- bability that a similar progression has taken place in all the sub-kingdoms. So far as our present knowledge goes, it would appear that there is such a progression in the Vertebrate sub- kingdom. The classes of Vertebrates make their appearance, on the whole, in the order indicated by their zoological posi- tion, the lowest first and the highest last. Not only does this hold good for the classes of the Vertebrates, but the same general statement may be made as to the orders of each class. Where apparent exceptions occur, a reasonable explanation can be given, or our knowledge can be shown to be defective. Space will not allow a discussion of this question, but a single example may be taken. So far as we know at present, the earliest remains of Vertebrate animals are those of Fishes the lowest class of the sub-kingdom and these appear in the Upper Silurian rocks for the first time. Granting the probability that Fishes may some day be found in the Lower Silurian rocks, or even in Cambrian deposits, there still seems no likelihood that they will be deprived by any future discoveries of their position as being the earliest of their sub-kingdom. The oldest remains of Fishes, however, are by no means those which would be expected, but belong to two of the higher orders of the class. This seeming anomaly, however, disappears when we consider that the two lowest orders of Fishes possess almost no struc- tures by which we can reasonably expect to find them re- corded in a fossil state. They may therefore have been in existence long before the Ganoids and Placoids of the Upper Silurian rocks, and we have no right to assume that they were not. As to the remaining great order of Fishes (the Teleostean Fishes), it is certain that their appearance was much later, and they are generally regarded as inferior to the Ganoids and Placoids in zoological position. This, how- GENERAL SUCCESSION OF ORGANIC TYPES. ever, is a matter of opinion, and reasons are not wanting for regarding them as the highest of their class. It only remains to add that nothing further is contended for here than the general fact of there having been a pro- gression of morphological types, the lowest presenting them- selves first, the highest being the last to appear upon the scene. It is by no means contended that the Ganoid Fishes of the Upper Silurian rocks were in any way degraded members of their ord^r, or inferior in point of organisation to the Ganoids of the present day. On the contrary, there is reason to think that many types early presented a de- velopment more varied than that exhibited by their suc- cessors. It is simply contended that, on the whole, there has been a zoological progression as we ascend from the Cambrian period to the present day. It is also to be remembered, that though the commencement of the Invertebrate sub- kingdoms may be unknown to us, a similar progression can be in many cases shown as regards the orders and classes of these, even more completely than in the case of the Verte- brate sub-kingdom. Lastly, the evidence of Palaeontology points, in the main, to the operation of some general law of evolution, whereby the later forms of life have been derived from the older ones. That this law has acted along with, and has sometimes been counteracted by, some other and as yet obscure law regu- lating the appearance of new types, seems equally certain ; but it is not necessary to enter upon this complex and im- perfectly understood question in this place. We are dealing here primarily with facts, and in the following pages we shall meet with unmistakable evidence of the operation of some law of evolution, while we shall, at the same time, find ourselves confronted with phenomena which, in the present state of our knowledge, appear to be irreconcilable with the universal or exclusive action of this law. It would be an easy solution of the difficulty to adopt the course of definitely accepting some hard-and-fast theory upon this subject, and to bring forward prominently all the known facts favouring this theory, while we left in comparative abeyance the facts pointing in other directions, or explained them away by 94 INTRODUCTION. more or less probable assumptions. Upon the whole, how- ever, it seems preferable to enter upon the study of the actual facts of the science of Palaeontology, as far as may be, unfettered by preconceptions and unpledged to theories ; while we may, at the same time, safely accept the doctrine of evo- lution, in the shape presented to us by the master-mind of Darwin, as an invaluable, indeed an indispensable, working hypothesis. PART II. P A L M Z L G- Y . PART II. CHAPTEE VII. SUB-KINGDOM I. PROTOZOA. SUB - KINGDOM I. PROTOZOA. Animal simple or composite, generally of very minute size, composed of a structureless 01* slightly differentiated, jelly -lifce, albuminoid substance (termed " sarcode "), showing no composition out of definite parts or segments, having no definite body-cavity, presenting no traces of a nervous system, and having either no alimentary apparatus, or but a very rudimentary one. TABLE OF THE DIVISIONS OF THE PROTOZOA. CLASS A. GREGARINID^E. Parasitic Protozoa, which are destitute of a mouth, and do not possess the power of emitting processes of their body- substance (pseud opodia). CLASS B. RHIZOPODA. Protozoa, which are destitute of a mouth, and have the power of emitting extensile and contractile processes of the body-substance (pseudopodia). Order 1. Monera. Ex. Protogenes. Order 2. Amcebea. Ex. Amoeba. Order 3. Foraminifera. Ex. Nummulites. Order 4. Radiolaria. Ex. Haliomma. Order 5. Spongida. Ex. Spongilla. CLASS C. INFUSORIA (Infusorian Animalcules). Protozoa mostly with a mouth, and rudimentary digestive canal ; destitute of the power of emitting pseudopodia ; furnished with vibratile cilia or contractile filaments ; the body usually with a distinct cuticle covering a layer of firm sarcode. VOL. I. ' G 98 PROTOZOA. Eegarded palseontologically, we may eliminate from the Protozoa the entire class of the Gregarinidce, with the Rhizo- podous orders of the Monera l and Amcebea, no trace of the past existence of which has yet been obtained, or, from their soft-bodied nature, is ever likely to be. For all practical purposes the same may be said of the large and universally- distributed class of the Infusorian Animalcules. 2 Some of these, however, possess horny or membranous cases, which might possibly be preserved in a fossil state ; and Ehrenberg has found in the flints of the Chalk certain microscopic bodies, which he regarded as being the protective carapaces of Peridinium and allied forms of Flagellate Infusoria. With this doubtful exception, however, no Infusorian ani- malcule has ever been detected in the fossil state, though the class has doubtless existed^ from the most remote an- tiquity. There remain, then, only the three Rhizopodous orders of the Foraminifera, Radiolaria, and Spongida, all of which secrete hard structures, and all of which are more or less extensively represented as fossils, so that they demand our attention separately and in detail. I. FORAMINIFERA. The Foraminifera may be denned as Kkizopoda in which the body is protected by a shell or " test," which is composed of carbonate of lime, or which may consist of particles of sand cemented together "by some animal cement, or may be simply horny (chitinous). The animal may be simple, or may repeat itself indefinitely by budding, and the body -substance gives out long and thread-like processes (pseudopodia) which interlace with one, another to form a network, and often coalesce at tlwir to form a continuous layer of sarcode outside the shelL 1 The "coccoliths" are sometimes regarded as being referable to the Monera ; but they will be considered here as belonging to the vegetable king- dom, and they will be briefly described in speaking of fossil Algae. 2 " Fossil Infusoria" are often spoken of as forming more or less extensive deposits in the earth's crust, but the organisms so named are really Diatom* and Polycystina, FORAMINIFERA. 99 The pseudopodia reach the exterior either ly perforations in the walls of the shell, or simply ~by the mouth of the latter (fig. 13, c I). Fig. 13. Morphology of Foraminifera. o, iTtfj/oia vulgaris, a monothalamous Foraminifer ; 7>, Miliola (after Schultze), showing the pseudopodia protruded from the oral aperture of the shell ; c, Discorbina (after Schultze), showing the nautiloid shell with the foramina in the shell-wall giving exit to pseudopodia ; d, Section of Nodosaria (after Carpenter) ; e, Nodosaria hispida; f, Globigerina bullaides. From a palseontological point of view the only part of a Foraminifer with which we have to deal is the shell or " test/' and there are several points to notice in this connec- tion. Firstly, as regards the actual composition of the shell, it is in the majority of cases calcareous, or composed of carbonate of lime, but it is rarely chitinous, and it is not uncommonly " arenaceous " that is, composed of particles of sand cemented together by some animal substance or by carbonate of lime. With the horny or chitinous Fora- minifera (Gromidce) we have nothing to do here, as they have never been, and are never likely to be, detected in a fossil condition. In the second place, the Foraminifera may be divided into two primary groups the Perforata and Imperforata accord- ing as the walls of the test are or are not perforated by pores or foramina, through which the pseudopodia reach the surface. In the imperforate calcareous Foraminifera the substance of 100 PKOTOZOA. the shell is " porcellanous," homogeneous, and opaque-white when viewed by reflected light. On the other hand, in those of the calcareous Foraminifera in which the walls of the test are perforated by pseudopodial apertures, the shell is " vitreous " or " hyaline," transparent and glassy, and often of a thin and delicate texture. The " arenaceous " Foramin- ifera are normally and typically " imperforate ; " but Mi- Henry Brady has shown that there exist forms (such as Valvulina, Nodosinella, and Endothyrci) in which the texture of the shell is arenaceous or sub-arenaceous, but the walls of which are sometimes porous, though more usually imper- forate. We are thus presented with a series of intermediate forms by which the gap between the Perforata and the Im- perforata is to some extent bridged over. Thirdly, as regards the form of the shell, great differences exist among the Foraminifera, and as concerns the mere external configuration, this is so variable that little or no value can be attached to it in classification. Moreover, in the two great series of the Perforate and the Imperforate Foraminifera it is common to find parallel or u isomorphic " groups. That is to say, we meet with two series of forms, repeating each other's peculiarities and variations in form, but the shell in the one series being perforate, while in the other it is imperforate. The simplest form among the Foraminifera is that of a single spheroid of sarcode, capable of secreting for itself a hard covering, as in the flask-shaped Lagena (fig. 13, ) or the globular Orbulina (fig. 14). Forms such as these are said to be " uni- locular" or " monothalamous," the test con- sisting .of but a single chamber, not sub- divided by partitions or " septa." In the Fig. 14. Or&wMua J , r . . . \ A simple more complex foramimfera, .the sarcode 01 the bod y undergoes a subdivision into par- beds) of tially separated segments, which may be pro- Italy. (D'Orbigny.) , V, ,* * i -, i , duced by a process of budding, or, perhaps, by the occurrence of constrictions in the growing protoplasm, and each of these segments becomes more or less com- pletely divided off from its neighbours, or enclosed by a FORAMINIFERA. i ' '*'/ ' J * IQ1 wall of shell. In these " multilocular " or " polythalammis;" Foraminifera, therefore, the shell ultimately comes to consist of a series of chambers, separated by partitions of the test, and filled with sarcode. The partitions, however, or "septa," between the different chambers, are perforated by one or more apertures, through which pass connecting bands, or " stolons," of sarcode ; so that the sarcode occupying the different chambers is united into a continuous and organic whole. Each segment may give out its own pseudopodia through perforations in its investing wall (fig. 13, c), or the pseudopodia may be simply emitted from the mouth of the shell by the last segment only (fig. 13, &). In any case the direction in which the segments are developed is governed by a determinate law, and differs in different species, the form ultimately assumed by the shell depending wholly upon this. The forms, however, assumed by the shells of Fora- minifera are extremely variable, even within the limits of a single species, and it would be impossible to notice even the chief types in this place. There are, however, two or three important variations which may be noticed. If the buds are thrown out from the primitive spherule in a linear series so as to form a shell composed of numerous chambers arranged in a straight line, we get such a type as Nbdosaria (fig. 13, e). When the new chambers are added in a spiral direction, each being a little larger than the one which pre- ceded it, and the coils of the spiral lying in the same plane, we get such a form as Discorbina (fig. 13, c), or Robulina (fig. 15). These are the so-called "nautiloid" Foraminifera, from the re- Fi - ^--cnsteiiarm (tobuiina) echiwta, a J . " nautiloid " Foraminifer. (D'Orbigny.) semblance of the shell, in figure, to that of the Pearly Nautilus. From this resem- blance the nautiloid Foraminifera were originally placed in the same class as the Ammonites (Cephalopoda), but their true position was shown by the examination of their soft parts. In the typical nautiloid shell the convolutions 102 PROTOZOA. the' spiral all lie in one plane; but in other cases, as in Eotalia (fig. 16), the shell becomes turreted or top-shaped, in consequence of the coils of the spiral passing obliquely round a central axis. Fig. 16. Rotalia Boueana. (D'Orbigny.) Ill a few types of the Foraminifera (e.g., in the Dactyl - oporidce, fig. 19) the successive chambers of the multilocular test have no direct communication with one another, and simply cohere by their walls. In the majority of the com- pound shells, the successive chambers are so produced, that the septum between any two of thehi is formed solely by the anterior wall of the older chamber, which thus constitutes the posterior wall of the newer one (fig. 13, e). In the highest types of the compound Foraminifera, however, each segment is provided with its own proper wall of shell, each segment, as it is produced, forming for itself a posterior wall which applies itself to the anterior wall of the preceding segment, so that each septum (" septal plane ") is composed of two lamellae, as seen in fig. 1 7, A (Carpenter). Moreover, " in the higher types of the hyaline or vitreous series we frequently meet with an ' intermediate ' or ' supplemental ' skeleton, formed by a secondary or exogenous deposit upon the outer walls of the chambers, by which they receive a great accession of strength. This deposit not only fills up what would otherwise be superficial hollows at the junctions of the chambers (fig. 17, A, d\ or (as in Polystomella) at the umbilical depression, but often forms a layer of considerable thickness over the whole surface, thus separating each whorl from that which encloses it ; and it is sometimes prolonged into outgrowths that give a very peculiar variety to the ordinary contour, as in some varieties of Rotalia and Poly- FORAMINIFERA. 103 stomella, but most characteristically in Calcarina (fig. 1*7, B), and the stellate form of Tinoporus. This intermediate or Fig. 17. A, Diagram of one of the higher forms of the vitreous Foraminifera, showing the double nature of the septa (6), the stolon-passages between successive chambers (a), and the .supplemental skeleton (rf) ; B, Test of Calcarina Spengleri, magnified twelve diameters, show- ing the spines formed by the supplemental skeleton ; c, Part of a section of the test of Calcarina, magnified fifty diameters, showing the tubulated "proper walls" of the chambers (?0, and the canal-system of the intermediate skeleton (d) ; D. Part of the test of Nummulina Jcnvigata, highly magnified, showing the canal-system of the septa (s), and marginal cord (n). (After Carpenter.) supplemental skeleton, wherever developed to any consider- able extent, is traversed by a set of ' canals/ which are usually arranged upon a systematic plan, and are sometimes distributed with considerable minuteness " (Carpenter). The canals of this system are doubtless filled in the living state by prolongations of the sarcode, which serve to keep up the vitality of the intermediate skeleton. This intermediate skeleton, with its canal-system, is largely developed in many of the highest and largest of the types of the Hyaline Fora- minifera, and very specially so in the ancient Eozoon, if this be rightly regarded as a Foraminifer. As regards the range of the Foraminifera in time, repre- 104 PROTOZOA. sentatives of this group are found in almost all formations in which calcareous rocks are developed, and if we admit Eozoon to be a member of this group, then the order dates from the Laurentian, and has been continued throughout the entire period represented by the known stratified rocks. The Foraminifera have also contributed notably to the formation of the solid crust of the earth, and have often built up mas- sive and widely extended limestones. Well-known examples of these foraminiferal limestones are the great Fusulina lime- stones of Eussia and North America and the Saccammina lime- stone of Britain, both of which belong to the Carboniferous period ; the White Chalk of the Cretaceous period ; and the Nummulitic limestone, Miliolite limestone, and Dactylopora limestones of the Tertiary period. The Chalk has been already alluded to (see p. 15), and we shall, have occasion to briefly notice the others of the above-mentioned limestones in speaking of the generic types which characterise them. Besides having largely officiated as lime-makers, the Fora- minifera have materially contributed to the formation of deposits of greensand at various periods of the earth's his- tory, and are known to be carrying on the same process at the present day. The green grains in such green sands as those of the Cretaceous period (as first shown by Professor Ehrenberg for similar green grains in the Lower Silurian of Kussia), seem to be often really casts of Foraminifera in glau- conite (silicate of iron and potash), from which the calcareous shell has been dissolved away. Similar green sands, similarly composed in part of internal casts of Foraminifera, are now being laid down in various of the warmer seas of the globe. All the recent Foraminifera (with the exception of the chi- tinous Gromidce) are exclusively marine in habit, and all the extinct members of the group were doubtless inhabitants of the sea. Like many other lowly organised forms, the Fora- minifera have been very " persistent " types of life. Various of the Palaeozoic genera have descended to us unchanged from the Palaeozoic period ; and the prevalent forms in the Chalk are hardly different from those of the Atlantic " ooze." Upon the whole, Dr Carpenter concludes that " there is no FORAMINIFERA. 105 evidence of any fundamental modification or advance of the Foraminiferous type from the Palaeozoic period to the pres- ent time." Lastly, the Foraminifera are not altogether reli- able tests as to the depth of water in which the deposits containing them were laid down. As a rule, they abound principally in warm and shallow seas. The " Globigerina ooze " of the deep Atlantic and Pacific occurs mainly at great depths, but though doubtless partly composed of forms which really lived at those depths, it is principally made up of the shells of Foraminifera which live at or near the surface of the sea. The White Chalk the ancient analogue of the Atlantic " ooze " may therefore^ have been laid down in any depth of water, since its prevalent types of Foramin- ifera were probably mainly surface-forms. CLASSIFICATION OF THE FORAMINIFERA. The classification of the Foraminifera has proved a matter of considerable dif- ficulty. The older arrangements were unnatural, as being based wholly on the form of the shell, a point in which the Foraminifera show a most marvellous variability. For this reason the artificial systems proposed by D'Orbigny and Max Schultze have now been generally abandoned, and their place has been taken by the schemes of classification put forward independently and almost simultaneously by Professor Von Reuss upon the Continent, and by Dr Carpenter, Mr Parker, and Professor T. Rupert Jones in this country. Both these arrangements agree in the essential feature that they divide the Foraminifera into two great primary divisions, in accord- ance with the nature of the shelly investment. In the one division (Imperforata), the test is not perforated by pseudo- podial apertures, and it may be either " arenaceous " or " por- cellanous." In the other division, the test is perforated by more or less numerous pseudopodial foramina, and to this division the name of Perforata is applied. The following tables exhibit the arrangements proposed by Carpenter, Parker, and Rupert Jones, on the one hand, and Reuss, on the other hand ; the former being the most natural, and the one most widely adopted : 106 PROTOZOA. A. CLASSIFICATION OF THE FORAMINIFERA, ACCORDING TO CARPENTER, PARKER, AND RUPERT JONES. SUB - ORDER I. IMPERFORATA. Test membranous, calcareous, or arenaceous, not perforated by pseudopodial foramina. Family 1. Gromida. 2. Miliolida. 3. Lituolida. SUB-ORDER II. PERFORATA. Test perforated by pseudopodial fora- mina, generally calcareous. Family 1. Lagenida. 2. Globigerinida. 3. Nummulinida. B. CLASSIFICATION OF THE FORAMINIFERA ACCORDING TO REUSS. I. FORAMINIFERA WITH A NON-PERFORATE TEST. A. With arenaceous tests. 1. Lituolidea. 2. Uvellidea. B. With compact, porcellanous, calcareous tests. 1. Squamulinidea. 2. Miliolidea. 3. Peneroplidea. 4. Orbitulitidea. II. FORAMINIFERA WITH A PERFORATE TEST. A. With a glassy, finely porous, calcareous test. 1. Spirillinidea. 2. Ovulitidea. 3. Rhabdoidea. 4. Cristellaridea. 5. Polymorphinidea. 6. Cryptostegia. 7. Textilaridea. 8. Cassidulinidea. B. With an exceedingly porous, calcareous test. 1. Rotalidea. C. With a calcareous shell, traversed by a ramified canal-system. 1. Polystomellidea. 2. Nummulitidea. With regard to the classification of the Foraminifcra, the author may advantageously quote some remarks on this sub- FORAMIXIFERA. 107 ject made by Mr Henry Bowman Brady, F.R.S., one of the highest living authorities on this group of organisms ; since they not only have a most important bearing upon the special point in question, but forcibly express the principles which should guide the philosophic naturalist in his syste- matic treatment of all such variable forms of life : "A purely artificial classification is ill adapted to the conditions presented by a class of organisms like the Foraminifera, largely made up of groups of which the modifications run in parallel lines. This 'isomorphism,' demonstrated chiefly by the labours of Messrs Parker and Jones, whilst it is the source of most of the difficulties the systematist has to con- tend with, is, at the same time, the key to the natural his- tory of the order. It exists not merely between a single series, say in one of the larger divisions, with a single series in another, but often amongst several series even of the same family. It not unfrequently happens that a member of one group presents a greater similarity to its isomorph in another group with which it has a relationship, than it does to any other member of its own group. Take a familiar illustration suppose the fingers of the two hands to represent the modifications (' species ') of two such parallel types of Fora- minifera : the thumb of one hand resembles more closely the thumb of the other hand than it does any other of the fingers on its own. In other words, the extreme member of one series resembles more closely its isomorph in the other series than it does its own nearer relations, and so on through the remaining members of the respective groups. Under condi- tions like these, artificial subdivision, based upon minor mor- phological characters; is certain to infringe the order of nature. Its tendency is to separate forms closely allied, and in many cases to place together such as have no close affinity." The principal fossil groups of Foraminifera deserve a brief consideration, but in the short summary of these which follows as in the case of similar summaries which will subsequently be given it must be understood that nothing further is proposed than to select for notice and characterisa- tion those leading types of each great group of fossils which 108 PROTOZOA. may seem to demand mention on the ground of their being common, or in other respects, geologically or zoologically, of peculiar importance. For anything like a complete list of the known structural types of each group, or the characters of the recorded genera, the specialist will consult special treat- ises ; and it does not appear to be necessary for the wants of ordinary students to do more than to supply a brief state- ment of the conspicuous characters especially the differen- tial characters of the more widely distributed and more important types in each group. Nor can even this limited characterisation of leading types be carried out with equal fulness in the case of all groups of fossils, or upon any abso- lutely uniform plan. In the case, however, of Invertebrate fossils, as being those with which the paleontologist is more especially called upon to deal, the families of each group will, where possible, be denned, and some of the chief generic types will be noticed. The subjoined engraving, representing some of the principal type-forms of the Foraminifera, is from a drawing kindly made for the author by his friend, Mr Henry Brady, F.R.S., who has so greatly contributed to our know- ledge of this difficult group of organisms. IMPERFORATE FORAMINIFERA. Among the Imperforata, we have the three families of the Gromida, Miliolida, and Litu- olida, of which the first needs no notice, as being quite unknown in the fossil condition. In the family of the Miliolida, the test is opaque, porcel- lanous, unilocular, or multilocular, and extremely variable in shape ; the oral aperture being simple and undivided, or being- formed by numerous pores. The family, as far as known at present, is not represented in the Palaeozoic period, but ranges from the Trias to the Kecent period inclusive. One of the simplest forms of this group is Cornuspira (fig. 18, a\ in which the shell is a simple unchambered spiral, like the shell of a Planorbis. The genus is represented in the early Ter- tiary, and is found under living forms in our seas. Nubecu- laria is a much older type, beginning in the Trias, and its test, extraordinarily variable in shape, is parasitic upon shells and other foreign bodies. In Miliola, again (fig. 18, &, representing the sub-generic form Quinqueloculina), the shell FORAMINIFERA. 109 is still extremely variable in form, but it consists typically of a series of chambers wound round an axis, in such a manner Fig. IS. Types of Foraininifera. a, Cornuspira foliacea; b, (Juinqiwloculina seminuluw ; c, Peneroplis pertusus ; d, Lihwla aggluthwns; e, Trochammina pusillus ; f, Lagena sulcata; g, Nodosaria radicula ; li, Marginulina ruphanus; i, Frondicukiria Archiaciana; j, Polymorphina lactea; fc, Globigerina bulloides ; I, Textularia sagittula ; m, Cassidulina Icevigata ; n, Bu'iminti r,uchlana;o, Rotalia Beccarii ; p, Truncatulina lobatula ; r, Arduediscus Karreri ; s, Polystom- ella crispa; t, Amphtetegina I^ssoni. All the figures are greatly enlarged, the real diameters varying from 1-100 to 1-10 inch. (H. B. Brady.) that each embraces half the entire circumference. This genus dates from the Jurassic (Lias), and is well represented in 110 PROTOZOA. recent seas. It abounded in Eocene times, one of the Tertiary limestones of the Paris basin being known as the " Miliolite limestone," in consequence of its being largely made up of the shells of a MUiola. In Peneroplis (fig. 18, c) the shell is a flattened spiral, which expands very rapidly in its last half turn, the mouth running along the length of the base, and being constituted by numerous isolated pores. It ranges from the Eocene to the present day. Much more complicated types of the Miliolida are .Alveolina and Orbit- olites. The former has a comparatively large fusiform shell, Fig. 19. Dactyloporidse. A, Dactylopora eruca (recent) magnified 30 diameters, and viewed from the inner face ; B, Dactylopora annulus, from the Eocene Tertiary, magnified 40 diam- eters, viewed in profile, and showing two superimposed rings ; c, The same viewed from above and similarly magnified ; D, Part of the column of Dactylopora reticulata (Tertiary), viewed in profile, and similarly enlarged ; E, Fragment of Muschelkalk, with tubes of Gyroporella cylin- drica, of the natural size ; F, Transverse section of a tube of the same, enlarged 10 diameters ; o, Vertical section of the same, enlarged 12 diameters. (Figs. A D are after Carpenter ; figs. E o are after Giimbel.) consisting of many layers of chambers rolled up spirally round an elongated axis, the last series opening by a row of pores ; and it dates from the Cretaceous, and has largely contributed to the formation of various of the Tertiary lime- stones. The latter is coin-shaped, sometimes more than half an inch in diameter, and very complex as regards the arrange- ment of its chambers. The genus is especially abundant in FOR AMINIFERA . Ill the Eocene Tertiary, but it dates from the Lias, and occurs plentifully in the recent seas. The last of the Miliolida which need notice are the aber- rant types, which may be grouped together in a sub-family under the name of Dactyloporidce. 1 The simplest forms of this curious group, such as Dactylopora eruca (fig. 19, a), consist of a series of isolated but coherent chambers, each with a single opening, disposed in a half ring, and either free, or more commonly parasitic on shells, and found in tropical seas at the present day. The fossil forms are similar in structure to the simple type just alluded to, but they form complete rings, and these rings are superimposed upon one another so as to form longer or shorter columns, closed at their lower end but open above (fig. 19, B G). Each ring is quite independent of the others, the orifices of the constituent chambers all opening into the central cavity (fig. 19, c) ; but in some of the fossil forms the place of the chambers is taken by canals, which, like the former, do not communicate with one another (fig. 1 9, F). The various members of the Dactyl- oporidce range from the Trias to the present day, and they have a special interest, from the fact that certain forms of them (Gryroporella, fig. 19, E) constitute vast masses of lime- stone in the Trias of the Bavarian and Tyrolese Alps. Coming next to the family of the Lituolida, we have to deal with imperforate Foraminifera, mostly with arenaceous tests, but sometimes sub-arenaceous in texture, and some- times composed of purely calcareous particles embedded in a calcareous cement. In Lituola itself, the type of the group, (fig. 18, d), the test is generally crosier-shaped, sometimes nautiloid, usually with a rough exterior, and composed of sand-grains agglutinated together. The genus ranges from the Carboniferous to the present day. An essentially Car- boniferous type is Endothyra, in which the shell is exactly like that of a Rotalia in shape, and which is found abund- 1 Of late years high authorities have brought forward strong evidence to prove that most or all of the Dactyloporidce are really calcareous Algce. The question cannot be discussed here in detail ; but until a final decision has been given by specialists in the department of the Foraminifera, it seems safest to retain the group in its present position. 112 PROTOZOA. antly in the Mountain Limestone of Britain. It forms in America entire beds of the Carboniferous Limestone (fig. 20). In Trochammina (fig. 18, e) the test is usually spiral, consisting of one or many chambers, free or at- tached, and, though sandy, with a smooth surface. It ranges from the Carboniferous to the present day. Valvu- lina (fig. 21) also generally has a spiral shell which may be free or attached, and is normally thick-walled, imper- forate, and sandy. Sometimes, Fig. 20.-Section of Carboniferous Lime- however, the shell is pOTOUS stone from Spergen Hill, Indiana, U.S., showing numerous large-sized Foraminifera and Smooth, and 111 Other (Endothyra) and a few oolitic grains mag- ,-, -, , . nified. (Original.) cases the sandy coating seems to be a mere incrustation on a calcareous and perforate shell, so that Valvulina may be regarded as a transitional type between the great series of the iinperf orate and perforate Foraminifera. The Fig. 21. A., Slice of limestone with Saccammina Carteri, enlarged 5 diameters ; B, Spheres of the same, of the natural size, exhibiting variations ; c, Valvulina palceotrochus, in profile ; and D, the same viewed from below, enlarged 45 diameters. All from the Carboniferous. (After Brady.) genus makes its first appearance in the Carboniferous of Britain, is abundant in the Tertiaries, and is represented in FORAMINIFERA. 113 our recent seas. Of the remaining types of the Lituolida, the genus Saecammina merits special mention as being the only Foraminifer which in Britain actually forms a limestone. It consists of free spherical, pyriform, or fusiform chambers (fig. 21), sometimes separate, sometimes united end to end in twos or threes, with thick, internally labyrinthic walls. The central chamber communicates with the exterior by a single aperture, and the average length of the chambers of the British Carboniferous species ($accammina Carteri, Brady) is as much as l-8th inch. It forms beds of lime- stone in the Carboniferous of the South of Scotland and North of England ; but the genus is not known to occur again till we meet it in the Post-Pliocene, and, in a living state, in the North Sea. The genus has also been found recently in the Lower Silurian rocks of Scotland. In the Nodosinella of the Carboniferous we have another curious type, closely resembling the well-known Nodosaria in form, but having a sub-arenaceous, imperforate test. A still more singular form is the Staclieia of the Carboniferous, in which the test is also sub-arenaceous and imperforate, but grows parasitically upon foreign bodies, in the shape of a crust composed of " an acervuline mass of chamberlets " (Brady). Lastly, we must place here the extraordinary and colossal extinct forms which have been described under the names of Parkeria l (Carpenter) and Loftmia (Brady). Both of these are arenaceous in texture, and both have a very complex and truly " labyrinthic " internal structure. Parkeria occurs in the Upper Greensand of Britain, in the form of spheres, which are sometimes over an inch in diameter ; while Lof- tusia is found in the Eocene Tertiary of Persia, and has a fusiform shell which may attain a length of between two and nearly three inches. PERFORATE FORAMINIFERA. The forms included under this head have a calcareous shell more or less freely perfor- ated by pseudopodial apertures, and they form a great series, of which only a few of the most important forms can be noticed here. 1 According to Mr Carter, ParJceria is a Hydrozoon allied to the recent Hydractinia. VOL. I. H 114 PROTOZOA. The first family under this section that of the Lagenida comprises " hyaline " or " vitreous " Foraminifera, with a calcareous shell, the walls of which are pierced by numerous minute pores, and are usually more or less strikingly thin and glassy. In the compound forms of this group the suc- cessive chambers have their posterior walls formed by the front wall of the preceding segment, so that the septa are always single, instead of being double, and there is never any " intermediate " skeleton. The family may be divided into two series, Lagena itself being the type of the one, while Nodosaria is the type of the other. In Lagena (fig. 18, /) the shell is simple, flask-shaped, unilocular, with a single prominent aperture. The genus commences in the Carboniferous, with a few rare forms, is further developed in the Secondary and Tertiary, and is well represented at the present day. Polymorpliina (fig. 18,y) is allied to Lagena, but it is multilocular, the chambers being usually arranged in a double series. It is represented in the Trias, and sur- vives under common types at the present day. In the series of which Nodosaria is the type, we have perforate Forami- nifera consisting of a succession of chambers, each of which is essentially similar to a Lagena, arranged in a series, which is usually nearly or quite straight, though sometimes spirally involuted. In Nodosaria itself (fig. 18, g) the chambers are simple, and are disposed in a straight line. It ranges from the Permian to the present day. Dentalina, ranging from the Carboniferous onwards, is fundamentally like Nodosaria, but the shell is bent like a bow. Vagimdina comprises forms similar to Nodosaria, but laterally compressed, and begins in the Trias. Marginulina (fig. 18, Ji) is slightly curved, or is sometimes crosier-shaped, and also starts in the Trias. Frondicularia (fig. 18, i) has the shell flattened out and leaf-like, and likewise makes its first appearance at the summit of the Trias. Lastly, Cristellaria (with Eobulina} comprises forms more or less spirally inrolled or crosier- shaped, which extend from the Chalk to the present day, and have a very wide development both individually and specifically. In the second family of the Perforate Foraminifera that FORAMIN1FERA. 115 of the Gldbigerinida are included by Dr Carpenter all those hyaline or vitreous Foraminifera which have their shell- substance coarsely perforated for the exit of the pseudopodia. There is sometimes, though not usually, a " supplemental " skeleton, and the chambers generally communicate with one another by a larger or smaller crescentic aperture, and not by circular pores. Three simple or unilocular types viz., Orlulina, Ovulites, and Spirillina, are known ; of which the first (fig. 14) is the most important. It has a spherical shell, with numerous large -sized pores distributed among the smaller ones ; and though its distribution at the present day is universal, its earliest appearance seems to be in the Miocene Tertiary. In Ovulites 1 the one-chambered ovate test possesses an aperture at both ends. It is found in the Eocene and Miocene. In Spirillina, again, the test is coiled into a flat spiral ; and, likewise commencing in the Eocene, it is continued to the present day. The type of the Globi- yerinida, however, is Globigerina itself (fig. 18, &), in which there is a polythalamous shell consisting of globose segments arranged in a turbinate spiral, or irregularly disposed. The chambers do not communicate with one another directly, but each opens by a special aper- ture into a deep central or um- bilical depression. In some forms (as also in Orlulina) the test, when perfect, ap- pears to be covered with long and extremely delicate spines. Globigerina dates from the Cretaceous (Trias?), and is extremely abundant. It is of special interest, as being the principal constituent of the " ooze " found at great depths in the larger oceans at the present day ; while its shells form an equally large portion of the White Chalk (see p. 15). The remaining members of the Globigerinida fall into two 1 Recent researches point to the view that Ovulites is a detached segment of a calcareous Alga, but further evidence is required before this conclusion is finally adopted. 116 PROTOZOA. great sections, typified respectively by Textularia and Eotalia. In Textularia itself (figs. 18, /, and 22) the test is generally conical or wedge-shaped, and consists of numerous chambers arranged in two alternate parallel series. Bigenerina is much the same as Textularia, except that the last-formed segments are disposed in a single and not a double series, and both make their first appearance in the Carboniferous, the latter being a common type in many formations, and being specially abundant in the Chalk. Bulimina (fig. 18, n), dating from the Trias onwards, consists of spheroidal segments which progressively increase in size, and form an oblique spiral ; while Cassidulina (fig. 18, m), ranging from the Miocene to the present day, though truly biserial, is more or less com- pletely rolled up, and may thus be regarded as an involute Textularia. Lastly, Chrysidalina, dating from the Chalk, is like Textularia, but is triserial. In the Eotaline series, the shell is typically composed " of a succession of coarsely porous or globigerine segments, arranged in a turbinoid spire, and communicating with each other by a crescentic aperture situated at the junction of the septal plane with the free surface of the convolution " (Car- penter). Such a form of shell is exhibited, for example, by Discorlina (fig. 13, c), which dates from the Chalk, and is found living in our seas. Pulvinulina, with a spiral, usually trochoid shell, differs from Discorbina in having a much more finely porous shell. By the researches of Mr Brady, this type has been carried back to the Carboniferous period ; and it is thus one of the earliest representatives of the Eotalines. In Eotalia itself (fig. 1 8, d), the test is also spiral and turbin- oid, but its structure is more complex than in the preceding, the shell-substance being compact and very finely porous ; while each chamber is enclosed by a complete wall of its own, and there are canal -like spaces between the two lamellae forming each septum. In these respects, Eotalia closely approaches the Nummuline type. The earliest Eo- talice appear in the Chalk, but the genus attains its maximum in the Tertiary period, and is well represented at the present day. The approximation to the Nummuline type is further manifested by Calcarina (fig. 1 7, B and c), in which the FORAMINIFERA. 117 shell is spiral and discoidal, with spur-like marginal append- ages, and with a well-developed " supplemental skeleton " and " canal-system." The genus has been shown by Brady to commence in the Carboniferous. In Planorbulina the shell is composed of numerous segments, at first spirally and then cyclically disposed. It dates from the Tertiary period, but the forms which are included under the sub^generic name of Truncatulina (fig. 18, p) commence in the Carboniferous. Tinoporus, dating from the Chalk, is in some respects inter- mediate between Calcarina and Planorlulina, its general form being like the former, while the irregular and partly cyclical arrangement of its chambers recalls the latter. There is also sometimes a " supplemental skeleton " and " canal-sys- tem." We may just mention, also, the genus Polytrema, though not yet known in the fossil state, since it has some curious resemblances to some forms of corals and Polyzoa. It forms crusts, or, more commonly, branched outgrowths, parasitically attached to foreign bodies ; and it consists of numerous intercommunicating irregular chambers, the walls of which are penetrated by an extensive system of capillary canals. Polytrema seems to be the representative in the Eotaline series of the singular genus Stacheia among the Inperforata. Lastly, the genus Involuting from the Lias, is usually placed among the Eotalines, though it presents some peculiarities which would remove it from this series, or would even place it altogether outside the section of the Perforate Foraminifera. Finally, we have the family of the Nummulinida, comprising the most complex and the most highly organised of all the Foraminifera. In the forms included under this head, the shell is compound, the successive chambers are enclosed each in its proper wall (as diagrammatically shown in fig. 17, A), there is almost always a well-developed " intermediate " or " supplemental " skeleton, which renders the shell strong and compact, and which is perforated by a " canal-system," origi- nating in the spaces between the two lamellae of which each septum is composed ; while the shell-substance is pierced by close-set and extremely fine tubules, the septa alone wanting these, so that contiguous chambers usually communicate by 118 PROTOZOA. but one large aperture. The form of the shell is typically a discoidal spiral or a cycloidal disc. There is a relationship of a decided character between the higher Eotalines and the Nummulinida, as exhibited by forms like Rot alia itself, and Calcarina on the one hand, and by Polystomella and AmpJiistegina on the other hand. In Polystomella (fig. 18, s) the shell is lenticular, discoidal, composed of successive chambers, which are prolonged into wing-like ("alar") prolongations, which extend inwards to the centre, thus concealing the earlier turns of the spire from view, while the centre itself is occupied by a solid cal- careous boss, penetrated by irregular canals. The " canal- system " is extraordinarily developed and very complex. Some of the simpler types of Polystomella are grouped to- gether under the name of Nonionina ; and the genus seems to make its first appearance in the Upper Chalk, being well represented in the Tertiaries, and surviving to the present day. AmpJiistegina still more closely approaches the Eotalines, with which it has sometimes been grouped. Its shell is spiral and discoidal (fig. 18, t\ usually more or less inequi- lateral, each chamber being saddle-shaped, and sending forth "alar" prolongations which reach nearly to the centre, where is placed a solid boss. The shell-substance, with exception of the septa and the central boss, is penetrated by numerous close-set, parallel, extremely minute tubules, but the " canal- system " is only imperfectly developed. Brady has shown that the genus occurs in the Carboniferous ; but with this exception it is Tertiary and Eecent. Another very ancient, and more anomalous, type of the Nummuline group is the Archcediscus of Mr Brady (fig. 18, r), which occurs also in the Carboniferous Limestone. In this curious form the test is " convoluted, rounded, more or less unsymmetrical ; formed of a non-septate tube coiled upon itself in a constantly varying direction ; the shell- wall trans- versed by very numerous parallel minute tubuli " (Brady). In the genus Nummulina itself (fig. 23) the shell is coin- shaped, of large size, sometimes as big as a florin, or larger, composed of numerous chambers arranged on one plane in a FORAMINIFERA. 119 regular spiral. Each chamber is saddle-shaped, the internal or " alar " prolongations of each extending to the centre, so that each revolution completely encloses and conceals from view all the preceding ones. The successive chambers com- municate by means of arched fissures, which perforate each septum, close to the periphery of the previous turn of the Fig. IZ.Nummulina nummularia. A, The shell viewed from above; B, The same, horizontally bisected ; c, The same vertically bisected ; D, Vertical section of part of the shell, highly magnified, showing the chambers of the median plane, the alar prolongations, and the tubuli of the shell-substance. Eocene Tertiary. spire, while secondary and irregular pores in the septa dis- charge the same function. The general shell-substance is traversed by extremely minute parallel tubuli (fig. 23, D) ; and there is a supplemental skeleton (forming the so-called " marginal cord "), which, together with the septa, is pene- trated by a well-developed and ramified " canal-system " (see fig. 17, D). By the researches of Mr Henry Brady, we know now that the range of the genus Nummulina in time must be carried back to the Carboniferous, one small form having been detected in the Mountain Limestone of Belgium. A few " Nummulites " have also been detected in strata of Jurassic and Cretaceous age, but the maximum development .of the genus is recorded in the early Tertiary period (Middle 120 PROTOZOA. Eocene). At this period in the earth's history we find the ISTummulites existing in extraordinary profusion, and building up the wide-spread and massive series of calcareous deposits which are known as the " Nummulitic Limestone." Accord- ing to Sir Charles Lyell, " the Nummulitic Limestone, with its characteristic fossils, plays a far more conspicuous part than any other Tertiary group in the solid framework of the earth's crust, whether in Europe, Asia, or Africa. It often attains a thickness of many thousand feet, and extends from the Alps to the Carpathians, and is in full force in the north of Africa, as in Algeria or Morocco. It has also been traced from Egypt, where it was largely quarried of old for the building of the Pyramids, into Asia Minor, and across Persia, by Bagdad, to the mouths of the Indus. It occurs not only in Cutch, but in the mountain-ranges which separate Scinde from Persia, and which form the passes leading to Cabul ; and it has been followed still further eastwards into India, as far as Eastern Bengal and the frontiers of China." In. the later Tertiary period, the genus underwent a striking de- generation ; and it is represented at the present day by only a few small forms, which are found in arctic, temperate, and tropical seas. Very closely allied to Nummulina, and of equal or even greater geological importance, is the genus Fusulina, the typical forms of which (fig. 24) are spindle-shaped in figure, and may be compared to a Nummulite drawn out at its umbilici. According to Brady, however, some spe- cies of Fusulina are discoidal and symmetrical, and thus not distinguisTiable in form from Nummulina ; while in other species the test is spherical. In internal structure, and es- pecially in the minute tubulation of the shell-substance, the genus approaches Nummulina, but a regular interseptal " canal-system " appears to be wanting, and the chambers are broken up into chamberlets. Most of the Fiisulince are of considerable size, often from a third to a half of an inch in length, and they often constitute massive beds of limestone, FORAMINIFERA. 121 which have been justly paralleled with the Nummulitic Limestone of the Eocene. Thus they form whole beds of the Carboniferous Limestone in .Eussia, Central Europe, Armenia, India, China, Japan, and the United States. Though pre-eminently Carboniferous, they ocour also in the Permian. The remaining types of the Nummulinida, with the excep- tion of the much-disputed Eozoon, can be merely alluded to here. The genus Orbitoides is extremely like Nummulina in external appearance and form, and has been often mis- taken for it, but it differs considerably in its internal struc- ture, and especially in the fact that its mode qf growth is cyclical instead of spiral, and the place of the " alar prolon- gations" of the chambers of the latter is taken by a multitude of chamberlets. The genus appears first at the summit of the Cretaceous, but it undergoes, along with its ally Num- mulina, an extraordinary development in the early Tertiary period, and it forms immense masses of Eocene limestone in the Southern United States, the West Indies, and in various parts of the Old World. A nearly allied genus is Cyclody- peus, which is also coin-shaped, and is strictly cyclical in its mode of growth. It occurs in the Miocene Tertiary, and the only known recent types attain an extraordinary size (over two inches in diameter). Operculina, again, is much more closely related to Nummulina proper in its internal structure, though it differs in form, owing to the fact that the chambers of the spirally -inrolled shell have no "alar prolongations," and thus approximate to the Eotaline type. The genus commences in the Upper Cretaceous, but is par- ticularly developed in the Eocene of the South of Europe and Africa. Lastly, Heterostegina (Tertiary and Eecent) differs from Operculina chiefly in having the principal cham- bers broken up into chamberlets by secondary septa. Finally, if we admit that it is truly a fossil, we must include here the singular body which is known as Eozoon Canadense. Upon the true nature of this body a long con- troversy has been carried on, into which it would be impos- sible and out of place to enter here. It is sufficient to say that while the highest living authorities upon this special 122 PROTOZOA. group of organisms regard Eozoon Canadense as an aberrant IsTummuline Foraminifer, there are other observers who look upon it as a purely mineral and inorganic structure. 1 If, however, we accept the Foraminiferal nature of Eozoon as, at any rate, highly probable, we are presented here with a type of extraordinary interest, not only from its intrinsic peculiarities, but also as the most ancient representative of the group of Foraminifera, and, indeed, as the oldest fossil which has yet been exhumed from the earth's crust. The structure known as Eozoon is found in various locali- ties in the Lower Laurentian limestones of Canada, in the form of isolated masses or spreading layers, which are com- posed of thin alternating laminse, arranged more or less con- centrically (fig. 25). The laminae of these masses are usually Fig. 25. Fragment of Eozoon, of the natural size, showing alternately laminse of loganite and dolomite. (After Dawson.) of different colours and composition ; one series being white, and composed of carbonate of lime whilst the laminae of the second series, alternate with the preceding, are green in colour, and are found by chemical analysis to consist of some silicate, generally serpentine or the closely related " loganite," or white pyroxene. In some instances, however, all the laminse are calcareous, the concentric arrangement still re- maining visible in consequence of the fact that the laminae 1 Since the above was written, Professor Mobius has published an elaborate treatise upon Eozoon, and has arrived at the conclusion that it is not truly organic. It would not appear, however, so far as the author is able to judge, that the arguments of Mobius are by any means decisive ; and it may safely be concluded that the last word on Eozoon has yet to be spoken. FORAMINIFERA. 123 are composed alternately of lighter and darker coloured lime- stone. When first discovered, the masses of HJozodf\weYQ supposed to be of a mineral nature ; but their striking general resem- blance to the undoubted fossils which will be subsequently spoken of under the name of Stromatopora was recognised by Sir William Logan, and specimens were submitted for minute examination, first to Principal Dawson, and subsequently to Dr W. B. Carpenter. After a careful microscopic examina- tion, these two distinguished observers came to the conclusion that Eozoon was truly organic, and in this opinion they were afterwards corroborated by other high authorities (Mr W. K. Parker, Professor Eupert Jones, Mr H. B. Brady, Professor Giimbel, &c.) Stated briefly, the structure of Eozoon, as exhibited by the microscope, is as follows : The concentrically-laminated mass of Eozoon, as described by Dr Carpenter and Principal Dawson, is composed of numerous calcareous layers, representing the original skele- ton of the organism (fig. 26, V). These calcareous layers serve to separate and define a series of chambers arranged in successive tiers, one above the other (fig. 26, A, B, c) ; and they are per- forated not only by pas- sages (fig. 26, c), which serve to place succes- sive tiers of chambers in communication, but also by a system of del- icate branching canals (fig. 26,rf). Moreover, the central and princi- pal portion of each calcareous layer, with the ramified canal- system just spoken of, is bounded both above and below by a thin lamina which has a structure of its own, and which Fig. 26. Diagram of a portion of Eozoon cut verti- cally. A, B, c, Three tiers of chambers communicating with one another by slightly constricted apertures ; a a, The true shell-wall, perforated by numerous delicate tubes; b b, The main calcareous skeleton ("intermedi- ate skeleton"); c, Passage of communication ("stolon- passage") from one tier of chambers to another; d, Ramifying tubes in the calcareous skeleton. (After Carpenter.) 124 PROTOZOA. may be regarded as the proper shell- wall (fig. 26, a a). This proper wall forms the actual lining of the chambers, as well as the outer surface of the whole mass ; and it is perforated with numerous fine vertical tubes (fig. 27, a a\ opening into the chambers and on the surface by corresponding fine pores. From the resemblance of this tubulated layer to similar struc- tures in the shell of the Nummulite, it is often spoken of as the " Nummuline layer." The chambers are sometimes piled up one above the other in an irregular manner ; but they are more commonly arranged in regular tiers, the separate chambers being marked off from one another by projections of the wall in the form of partitions, which are so far imperfect as to allow of a free communication between contiguous chambers. In the original condition of the organism, all these chambers, of course, must have been Fig. 27. Portion of one of the calcareous layers of Eozoon, magnified 100 diameters. a a, The proper wall (" Nummuline layer ") of one of the chambers, showing the fine vertical tubuli with which it is penetrated, and which are slightly bent along the line a' a' ; c c, The intermediate skeleton, with numerous branched canals. The oblique lines are the cleavage planes of the carbonate of lime, extending across both the intermediate skeleton and the proper walL (After Carpenter.) filled with living matter ; but they are found in the present state of the fossil to be generally filled with some silicate, such as serpentine, which not only fills the actual chambers, but has also penetrated the minute tubes of the proper wall and the branching canals of the intermediate skeleton. In FORAMINIFERA. 125 some cases the chambers are simply filled with crystalline carbonate of lime. When the originally porous fossil has been permeated by a silicate, it is possible to dissolve away the whole of the calcareous skeleton by means of acids, leaving an accurate and beautiful cast of the chambers and the tubes connected with them in the insoluble silicate. From the point of view that Eozoon is truly Foraminiferal, it must be regarded as a gigantic member of the Nummu- linida, which must have grown in reef-like masses. It also has decided affinities to the Eotaline genera Polytrema and Calcarina, resembling the former in its irregular mode of growth, while it approaches the latter in intimate structure. The test in Eozoon is distinctly of a Nummuline type, as shown by its possessing a minutely porous or tubular " proper wall " to the sarcode-chambers, while there is also a largely developed " intermediate " or " supplemental " skeleton, pene- trated by a " canal-system ; " but it differs from all the known Nummulinida in its indefinite and often " acervuline " mode of increase. The minute structure of the test will be readily understood by comparing figs. 26 and 27 with fig. 17 c, the latter representing a much-enlarged view of part of the test of Calcarina. On the other hand, Professors King and Eowney, Mr Carter, and others, maintain that Eozoon is inorganic, and that its so - called " proper wall " is really nothing more than fibrous serpentine. Eozoon Canadense occurs in the crystalline metamorphic limestones of the Lower Laurentian in Canada, and it has also been detected in the same country in similar limestones believed to be of the age of the Upper Laurentian or Hu- ronian. An allied form (species ?) has been found in rocks supposed to be Laurentian in Newfoundland ; Dr Giimbel has described a third form from crystalline limestone belong- ing to the " Hercynian gneiss formation " (Lower Cambrian or Huronian ?) of Bavaria ; while similar structures are stated to occur in the serpentinous marbles of Connemara in Ireland (which are thought to be of Lower Silurian age). Lastly, Dr Dawson has given the name of Archceosphcerince to small spherical masses of serpentine, sometimes single, sometimes united together in small numbers, which he finds 126 PROTOZOA. in the Laurentian limestones of Canada, and which he states to be surrounded by a tubulated calcareous shell, resembling the " proper wall " of Eozoon. He is of opinion that these bodies are either detached chamberlets of Eozoon, or that they are independent organisms, allied to Eozoon, but of a simpler type. EECEPTACULITES. Before leaving the Fomminifera, we must briefly consider the curious fossils grouped together under the name of Receptaculites (figs. 28 and 29), which appear to constitute an aberrant type of the Foraminifera. If truly referable to this group of animals, Eeceptaculites is not only highly abnor- mal in point of magnitude, being sometimes as much as a foot in diameter, but its actual structure is quite anomal- ous. The genus includes large fossils, which are usu- ally discoid, basin-shaped, funnel - shaped, cylindrical or globular in shape, and which consist of a large central cavity, probably filled with sarcode in the living condition (fig. 28), surrounded by a thick wall of complicated struc- ture. In the cup-shaped forms (fig. 29, A) this central cavity is widely open above; but in the globular forms, according to Billings, it communicates with the exterior by but a small aperture situated on the upper surface (fig. 28). The wall bounding the central chamber is composed of (1) an external integument, (2) an internal integument, and (3) an intermediate space crossed perpendicularly by more or less closely approximated tubular pillars (fig. 28, and fig. 29, c). Both the outer and inner Fig. 28. Diagram of the structure of Recep- taculites, as it would be shown by a vertical sec- tion of a perfect specimen, a, The aperture at the summit ; b, The inner integument ; c, The outer integument ; n, The usual position of the nucleus ; v, The great internal cavity. The unshaded bands running from the outer to the inner integument represent the pillars. (After Billings.) RECEPTACULITES. 127 integuments of the wall are composed of numerous rhom- boidal calcareous plates (fig. 29, B), closely fitting together, and arranged in obliquely-curved intersecting rows, giving fragments of the fossil very much the appearance of the engine-turned case of a watch. According to Billings, the points of junction of each quartette of plates in the inner integument are pierced by foramina (see fig. 28), which allow of a communication between the central cavity and Fig 29. Morphology of Receptaculites. A, Outline of a perfect, basin-shaped specimen of Ilceeptaculites Neptuni, viewed in profile, of the natural size ; B, Part of the outer integument of the same, enlarged two diameters, and so far weathered as to show the canals radiating from the summit of the radial pillars ; c, Side view of a fragment of the same, showing the radial pillars uniting the inner and outer integuments ; D, Vertical section of the same, magnified, showing the outer and inner integuments (o and i), and the central canals of the pillars. From the Devonian of Germany. (After Gumbel.) the intercolumnar spaces of the wall ; but no such apertures could be detected by Gumbel in the specimens examined by him ; and he thinks that this communication is effected by means of minute, microscopic canals between the edges of contiguous plates. The last-named observer has also shown that the radial pillars of the wall are thick and nearly solid, but are perforated by a central tube or canal (fig. 29, D), 128 PROTOZOA. while their substance is composed of calcareous fibres ar- ranged in a feather-like manner. Each pillar, further, is attached to the centre of one of the plates of both the outer and inner integuments, and the central tube of the pillar opens into a system of horizontal canals which penetrate the substance of these plates. In the plates of the outer integu- ment there are four of these canals, springing from the main tube of the pillar, directed towards the four angles of the plate, defended by rib-like thickenings of the plate, and often laid open by weathering (see fig. 29, B). In the plates of the inner integument, on the other hand, the horizontal canals are smaller, less clearly quadripartite, and more or less ramified. As to its affinities, Mr Salter regarded Eeceptaculites as a Foraminifer, and he placed it in the neighbourhood of Orbito- lites. Mr Billings, however, pointed out that the genus has some curious points of resemblance to the " gemmule " of the fresh- water sponges, and he regarded it as being upon the whole a sponge, having relationships with the Foraminifera. The most recent researches upon the genus, by Giimbel, indicate its proper position to be probably with the Foraminifera, though it can hardly be placed in the immediate neighbour- hood of any of the families of this order. The genus is pre-eminently Silurian and Devonian, but Suess has indi- cated its existence in rocks of Carboniferous age. It seems likely that some problematical types, which have been doubt- fully referred to the Sponges, to the Tunicates, or even to the Cystideans, may really belong to the same family with Ee- ceptaculites. This may be the ultimate destination of the various singular bodies described by Billings as Pasceolus, by Eichwald as Cydovrinus, by Salter as Nidulites, and by Pen- gelly as Sphcerospongia, the true nature of all these being still uncertain ; but the little that need be said about these problematical forms will be given when treating of the Cys- tideans. In any case, the Silurian genera described under the names of Isckadites and Tetragonis are certainly the same as Eeceptaculites. 129 CHAPTER VIII. SUB-KINGDOM I. PROTOZOA (Continued}. RADIOLARIA AND SPONGIDA. II. EADIOLARIA. UNDER the head of Radiolaria are grouped together at the present day various, mostly microscopic, Protozoans which typically possess a siliceous skeleton, the parts of which are often more or less radiate, the sarcode of the body being differentiated into a central mass, surrounded ly a membranous capsule, and an outer layer usually containing cell -like bodies, while the pseudopodia are long, filamentous, and ray - like (fig. 30). Though the typical Eadiolarians are distinguished by the above-mentioned characters, some of the forms which must be included here are devoid of certain of these features. Thus the so-called Heliozoa have no central capsule, and only occasionally possess skeletal structures. In other cases, though the general type of the group is retained, the skeleton is wholly wanting, while the nature of the skeleton when present varies greatly. From the last-mentioned point of view, the Eadiolarians are divided into four groups. In the first of these there is no skeleton at all ; we have therefore nothing to do with these as fossils. In the second group are forms in which there is a skeleton, but this consists merely of scattered spicules, which lie wholly outside the central capsule of the body ; and these also are unknown as fossils. In the third group are forms with a skeleton of radial spicules, but these are now disposed as a symmetrical VOL. I. I 130 PROTOZOA. whole, and lie partly inside the central capsule as well as outside it. In this group are forms like Acanthometm (fig. 30, a) ; but though capable of preservation, these forms, like Fig. 30. Recent Radiolaria. a, Acanthometra ; b, Actinomma (Haliomma), one of the Polycystina, showing the siliceous test and radiating pseudopodia. the preceding, do not occur in the fossil state. Lastly, we have a group in which there is a siliceous, fenestrated or perforated, coherent shell or " test," which is usually fur- nished with projecting spines. In this group are the micro- scopic marine organisms, well known for their beautiful glassy skeletons, to which the name of Polycystina was given by Ehrenberg. Many forms of the Polycystina have been preserved in the fossil condition, and the distribution of the Radiolaria in time, so far as known, is thus identical with that of this particular section of the order. The earliest 1 undoubted remains of Polycystina occur in the Jurassic series, and several well-marked types have been detected in the Chalk. All the remaining fossil Polycystina are referable to the Tertiary period ; and the two most famous localities in which they occur are Barbadoes and the Nicobar Islands. In the former island, in particular, is found a great deposit of sandstone and marls, which rises to heights of over 1000 feet above the sea-level, and which is fundamentally composed of the sili- ceous skeletons of Polycystina (fig. 7). The "Barbadoes 1 Some forms of Polycystina have been indicated as occurring in the Trias. Some Carboniferous fossils have also been referred to this order, but these supposed ancient Eadiolarians appear to be really of a vegetable nature. KADIOLARIA. 131 \ earth," as this deposit is generally called, is thus a Tertiary representative of the " Eadiolarian ooze," which has been shown by Sir Wyville Thomson to cover large areas of the ocean-bed, up to the enormous depth of 4500 fathoms, and which is likewise principally made up of the shells of Poly- cystines. As is the case, however, with the Globigerince, the Polycystines are principally surface -forms, inhabiting the open ocean, so that a deposit formed of their shells can in no way be regarded as indicating necessarily the depth of the sea in which it was laid down. There are many known recent types of Polycystina which have not yet been detected in a fossil state ; and the prin- cipal fossil forms are the following : One of the simplest, Fig. 31. Types of Polycystina. a, Podocyrtis Schomburgki ; 6, Dictyomitra Mongolfieri; c, Haliomma dixiphos; d, Dictyocha Messanensis; e, Eucyrtidium elegans; f, Lychnocanium lucerna. d is living, and is after Hseckel ; the remaining are Tertiary, and are after Ehre'n- berg. All the figures are greatly enlarged. and it is also the most ancient, of the fossil types is Cozno- spJwcra (sometimes referred to the Thalassicollicla), which is found in the Jurassic and Cretaceous, and has survived to the present day. Of the typical Polycystines, Haliomma (fig. 31, c), Heliodiscus, Actinomma (fig. 30, 6), and Didymo- cyrtis, represent those forms in which the skeleton consists of two, three, or more porous spherical shells, included concen- 132 PROTOZOA. trically within one another, the smaller within the larger, and united by radial bars. Most of the fossil forms, how- ever, belong to the type in which the shells are in the shape of a porous siliceous trellis-work, which may be quite un- divided, or is partially marked off into two or more compart- ments by longitudinal or transverse constrictions. The two poles of the shell are quite unlike one another, and the central membranous capsule of the living animal is enclosed within the closed apical pole. As examples of this type, we may select the genera Podocyrtis, Eucyrtidium, Lychnocanium, and Dictyomitra (see fig. 31), all of which are found in the Tertiary, and the last of which is represented in the Chalk. In another group, of which Dictyocha (fig. 31, d) is the type, the skeleton is composed of irregular bars of flint united into a loose network with wide meshes. This type begins in the Chalk, and is represented in the Tertiary deposits and in recent seas. Lastly, we have a group in which the skeleton consists of a flat or lenticular and biconvex plate, which is sometimes double, and has a more or less complex inter- nal structure. As examples of this group, we may select Astromma, Trematodiscus, Ehopalastrum, Stephanastrum, and Stylodictya, the last of which begins in the Chalk, while the others are represented in the Tertiary. * III. SPONGIDA. The Sponges may be defined as Ehizopoda composed of numerous amazbiform masses of sarcode united into a composite mass, which is traversed by canals opening on the surface, and is almost always supported ly an internal skeleton or framework of horny fibres or of calcareous or siliceous spicula. The only portion of the Sponges with which the palaeontol- ogist is concerned, is the skeleton. Whatever the nature of the skeleton may be, it is so arranged that its parts surround two sets of apertures which open on the surface of the sponge, and which are connected with one another by a system of canals ramifying in its deeper portions. Of the apertures which penetrate the substance of the sponge in every direc- tion, one set consists of large chimney-like openings, which SPONGIDA. 133 ' are called " oscula," or " exhalant apertures." There may be only a single osculum, or many may be present. The other set consists of very much smaller openings, which are always very numerous, and which are termed the "pores," or " inhalant apertures." The pores and oscula are connected by a system of canals excavated in the substance of the sponge, and a constant circulation of water can be kept up through the whole mass, the former serving for the incoming currents, the latter for the outgoing. The Sponges are by far the largest of the Protozoa, and, as above defined, they consist of a soft basis of living proto- plasm, which, with hardly an exception, is supported by certain skeletal structures, which vary in composition and arrangement, and are more or less capable of being preserved in a fossil condition. As the soft parts of the Sponges seem to be essentially identical, and as it is only the supporting framework or skeleton which is capable of undergoing petri- faction, we may divide Sponges according to the nature of their hard parts into the following three groups : 1. THE HORNY SPONGES (Keratoda), in which the skeleton is composed of a substance allied to horn, and consists of innumerable fibres matted and felted together, so as to give rise to a very variably-shaped mass. The fibres may be solid or hollow, and the skeleton may consist wholly of these, or may be more or less extensively strengthened by means of vari- ously-shaped microscopic spic- ules of flint (fig. 32). The horny framework of Sponges such as these is obviously in- capable of preservation in the . Fig. 32. Fragment of the skeleton of lOSSll Condition ; UnleSS We SUp- a horny sponge (after Bowerbank), greatly pose (what has not been proved Sj^l owing ta to occur) that it may be re- placed, during the process of petrifaction, by flint or car- bonate of lime ; while the spicules which are often present, 134 PROTOZOA. though doubtless capable of preservation, and though prob- ably often really present in the rocks, can be with difficulty detected, from their minute size, and can hardly be said to be known with certainty except in the Secondary and Ter- tiary deposits. Many fossil Sponges have, it is true, been referred by different observers to the section of the Horny Sponges, but it is now certain that most of these are certainly truly Siliceous Sponges, while the others are equally referable to other groups. An exception to the above statement must be made in favour of the aberrant group of living Sponges known as the Clionidce. In all formations, from the Lower Silurian onwards, we meet with shells and corals mined with winding- tunnels or borings, which have a circular cross-section. These tunnels are usually regarded as being the work of Sponges belonging to the living genus Cliona (Vioa), or to forms closely allied to this ; and in many instances this reference is doubtless correct. It must not be forgotten, however, that it is very difficult, or impossible, to distinguish, in the case of fossils, between the borings made by Sponges and those produced by Annelides or by carnivorous Gasteropods. Gei- nitz has also described from the Permian rocks a sponge to which he gives the name of Spongil^sis, and which he regards as being most nearly allied to the living fresh- water sponges (Spongilla). Lastly, we meet with the remains of Sponges, as yet undescribed, in the Lower Silurian rocks of Britain, which show some indications of having been origin- ally horny. Of this nature, perhaps, is the cup-shaped Proto- spongia of Salter ; but the minute structure of this old type is still very imperfectly known. 2. THE CALCAREOUS SPONGES (Calcispongice). The Sponges included in this group are invariably furnished with a cal- careous skeleton, which, in all the living species, is composed of spicula of lime, usually fusiform or triradiate in shape, and always entirely free and independent of each other. No living member of the Calcispongice, then, is possessed of a continuous skeleton, and the calcareous spicules which con- stitute the sole skeletal elements are microscopic in their dimensions ; so we might have anticipated beforehand that we should find few representatives of this group of Sponges SPONGIDA. 135 in past time. Of the fossil forms, indeed, hardly any can be said to be true Calcispongice, if we restrict this name to Sponges with a skeleton composed of free calcareous spicula ; and some doubt attaches to even the very few forms which one might be disposed to place here. Two ancient genera viz., Astrceospongia and Amphispongia may, however, be more specially mentioned, as being, perhaps, ancestral types of the modern Calcispongice. In Astrceospongia (fig. 33, a), we have Fig. 33. a, Side-view of a specimen of Astrceospongia meniscus, of the natural size, Upper Silurian ; ft, Spicules of the same, enlarged (after Roemer) ; c, A split specimen of Amphi- spongia oblonga, of the natural size, Upper Silurian ; d, Part of the upper portion of the same, enlarged. (Original.) a cup-shaped or discoid sponge, found in the Upper Silurian and Devonian, and composed of irregularly disposed, free, six- rayed, calcareous spicula, without any definite canal-system. The rays of the spicules are all in one plane, and their size is much greater than that of the spicules of any living member of the Calcispongice, but there is no sufficient reason for regarding them as having been anything but calcareous to begin with, since they occur in beds in which the other fossils have undergone no change. The genus Amphispongia (fig. 33, c) is another curious type, which approximates to the living Calcispongice more closely than the preceding. It is only known from certain soft sandstones, of Upper Silurian age, in the Pentland Hills, near Edinburgh ; and, like almost all the other fossils in the same beds, its original calcareous skeleton has been dissolved away, but we are not thereby justified in concluding that its hard parts were primitively composed of anything but lime. The general form of this sponge is that of a somewhat clavate mass, between one and two inches long, and, owing to its 136 PROTOZOA. peculiar state of preservation, the spicules which formed the original skeleton are now only represented by vacant spaces or cavities, while the actual canals and intervals between these are filled with the sandy matrix of the rock. The lower part of the sponge (fig. 33, c) consists of a series of radiating canals, separated by a series of calcareous bars or bundles of spicules, the former now filled with the surround- ing matrix, while the latter, being dissolved out, are repre- sented by hollow tubes. The upper part of the sponge, on the other hand, is composed of a matted mass of small spicules, now represented only by cavities (fig. 33, d). These spicules are so closely fitted together that their form is very difficult to make out ; but, according to the apparently correct observa- tions of Salter, they are composed of three rays, two of which lie in the same plane and form a continuous line, while the third springs from the point of junction of the other two, and is directed at right angles to them. In the opinion of Salter and Bowerbank, Ampliispongia is closely allied to the living- genus Gfrantia, and, under any circumstances, there can be little doubt as to its being truly an ancient type of the Calcispongice. While all the living Calcispongice possess a skeleton com- posed of disconnected spicules, there is no a priori reason why we should not meet with fossil forms of an essentially similar nature, but having a continuous or vermicidate skeleton, com- posed of calcareous spicules primitively free, but ultimately anchylosed so as to form a single and connected framework. Many fossil sponges have been supposed to belong to this now unrepresented category of Calcispongice with a continuous skeleton, but most of them (including most of the forms for- merly known as Petrospongiadce) have been shown by recent microscopic researches to be truly siliceous sponges. 1 There still remain, however, some fossils which were beyond all question calcareous to begin with, and which cannot, with our present knowledge, be assigned to a definite place in the zoological series, unless we regard them, provisionally at any 1 Since the above was written, Zittel has published a memoir in which he refers a large number of Triassic, Jurassic, and Cretaceous Sponges to a special group of Calcispongice in which the skeleton is fibrous and continuous, instead of being composed of separate spicules. The principal types referred to this group are the genera Peronella and Corynella. The apparently fibrous skele- ton of these forms is stated to be really composed of spicula. SPONGIDA. 137 rate, as a group of Calcareous Sponges with a continuous skeleton thus giving us a link between the Spongida and the Foraminifera. Of the fossils referred to, we need only speak more particularly here of the abundant Palaeozoic forms which have usually been grouped together by palaeontologists under the name of Stromatopora, and of the singular forms com- posing the genus Archceocyathus. The genus Stromatopora using this term in a purely general sense comprises a great number of Silurian and Devonian (possibly also Carboniferous) fossils, which form hemispherical, globular, or irregular masses, varying from an inch or less up to many feet in diameter, and which are always composed essentially of closely ap- proximated calcareous laminae (fig. 34) arranged concentri- cally round one or more centres, and often demonstrably Fig. 34. A small and perfect specimen of Stromatopora rugosa (Hall). From the Memoirs of the Geological Survey of Canada. attached to foreign bodies. Sometimes they form thinner or thicker crusts, growing parasitically on shells or corals, or spreading out as horizontal expansions. The concentric laminae, which are the essential feature of this group of fossils (and which strongly call to mind the appearance of masses of Eozoori), are separated by wider or narrower interspaces, which are more or less completely subdivided by vertical 138 PROTOZOA. pillars or imperfect partitions (fig. 35). We might readily be disposed to regard these singular forms as aberrant and gigantic Foraminifera, but in no case has it been satisfac- torily proved that the calcareous walls of the fossil are Fig. 35. a, Fragment of Stromatopora granulata (Devonian), of the natural size, showing the upper surface, with stellate water-canals ; &, Vertical transparent section of the same, magnified ; c, Horizontal transparent section of the same enlarged still further ; d, Vertical section of another Stromatoporoid (Clathrodictyon cellulosum), enlarged. In figs, b and c the skeleton is dark, and the light spaces represent transparent calcite ; but in fig. d the latter represent an infilling of silica. (Original.) penetrated by microscopic tubuli. The spaces between the successive laminae are, however, placed in communication by means of a more or less largely developed series of pores, and we can hardly avoid the conclusion that the entire fossil in its living condition was permeated by continuous sar- code ; so that we must regard it as referable to the sub- kingdom of the Protozoa. The mass of the fossil is also often penetrated by larger or smaller canals, which can hardly have served any other purpose than that of con- veying water to different parts of the organism (fig. 36, a), and which may fairly be compared with the " aquiferous canals " of the Sponges. The surface of the mass, also, often exhibits conical elevations, or papillae, which are perforated at their summits by the apertures of water-canals, and from which there radiate branched and vermiculate grooves, these char- acters strongly reminding us of some of the living Sponges (see fig. 35). It should be added that many palaeontologists SPONGIDA. 139 are disposed to take a different view of the affinities of the " Stromatoporoids," and to place them among the Hydrozoa, in the sub-class of the " Hydrocorallines." This view seems to be based principally upon the curious Devonian genus Caunopora, which differs from Stromatopora proper in many important respects, and the structure of which in spite of many able researches has still to be fully worked out. Fig. 36. a, Part of the under surface of Stromatopora tuberculata, showing the wrinkled basement membrane and the openings of water-canals, of the natural size; 6, Portion of the upper surface of the same, enlarged; c, Vertical section of a fragment, magnified to show the internal structure. Corniferous Limestone, Canada. (Original.) Upon the whole, therefore, we must at present regard the position of Stromatopora and its allies as uncertain. In the genus Archceocyathus (fig. 37), we have a group of singular fossils which have been described by Mr Billings from the summit of the Cambrian and the base of the Lower Silurian (Potsdam Sandstone and Calciferous Sand-rock), in North America, and have been subsequently investigated by Principal Dawson. The general form of the fossils herein included is that of a hollow cone or hollow cylinder, enclos- ing a large cup - shaped cavity, and tapering towards one extremity, which was presumably fixed to some foreign body. 140 PKOTOZOA. Specimens appear to have reached a very large size, a length of two or three feet and a diameter of three or four inches being sometimes attained. The sponge consists of an outer wall, usually perforated with numerous small irregular aper- tures, and a thin inner wall pierced with many openings (fig. 37, a). The space between the outer and inner wall is subdivided by a number of vertical radiating partitions, thus simulating the structure of one of the septate corals. The genus, however, is cer- tainly not a coral, and we have the curious feature of the occurrence of numerous branching, cylindrical, or fusi- form siliceous spicula within the substance of the organism. In the same geological hori- zon, and also in higher strata, occurs the somewhat allied genus Calathium, in which the skeleton also assumed a turbinate form. According to Dawson, the vertical la- minse or septa in the upper portion of the cup of Archceocyathus are not only perforated by numerous round apertures thus allowing contiguous chambers to communicate freely with one another, but they are themselves traversed by branching delicate canals running in their substance ; and he regards the genus as in some respects allied to Eozoon. Lastly, it is possible that, in the Carboniferous genus Palceacis, often referred to the Perforate Corals, we have in reality a type of calcareous Sponges, with a vermiculate skeleton. 3. THE SILICEOUS SPONGES (Silicispongice). In this group are included those Sponges in which the skeleton is made up of siliceous spicula or fibres. The skeleton may be a discontinuous or continuous one, and in the living forms the sarcode contains free siliceous spicules of microscopic size and very variable form. These " flesh-spicules," though Fig. 37. Kestoration of the lower part of Archceocyathus Minganensis. a, The pores of the inner wall of the cup. (After Billings.) , SPONGIDA. / 141 often met with in the rocks, are of comparatively little use to the palaeontologist so far as enabling him to classify the fossil forms is concerned, since it is rarely possible to refer them to the Sponge to which they originally belonged. They are, however, of great use in the determination of the living types. The spicules of the true skeleton, on the other hand, are usually united to one another by a sort of articulation, or become cemented together by a deposit of glassy silica ; so that the skeleton forms a more or less continuous framework, admirably adapted for preservation in a fossil condition. Until of late years very little was known, with any pre- cision, as to the structure, affinities, or real nature of a great many fossil Sponges, which are now recognised as belonging to the group at present under consideration. This arose partly from the fact that the value of the microscope in palaeon- tology had not been recognised, and partly from the fact that the structure of the living types has only recently been at all fully understood ; while the state of preservation in which these fossils often occur was such as almost inevitably to lead to misconceptions as to their nature, and to give rise to difficulties which are even yet not fully cleared up. It was known, namely, that Sponges with a siliceous skeleton were of common occurrence in various formations, and especially in the Jurassic and Cretaceous rocks ; but it was generally sup- posed that in these cases the skeleton had been originally composed of lime or of horn, which had in the process of ibssilisation been dissolved away and replaced by flint. These Sponges, in fact, were supposed to have undergone silicification a change to which we know that fossils are very often sub- jected. In the face of the now recognised fact that the minute structure of these fossil forms agrees perfectly with that of living siliceous Sponges, and differs wholly from that of any living types of calcareous or horny Sponges, we can- not doubt that their skeleton was primarily composed of flint. We are thus compelled to believe that in many instances the original siliceous skeleton has been more or less completely dissolved away, the space which it originally occupied in the rock being left permanently vacant, or being simultaneously or subsequently filled up with peroxide of iron, 142 PROTOZOA. or with crystalline carbonate of lime. Though this dissolution of a flinty skeleton, with or without replacement by lime, is at variance with all preconceived ideas on this subject, and though it is very difficult to give any adequate or satisfactory explanation of the way in which it is effected, the researches of Prof. Zittel and Mr Sollas hardly allow us to doubt its actual occurrence in nature. It is impossible here to pursue this intricate and still controverted subject further ; but it may be pointed out that in this dissolution of the skeletons of siliceous Sponges (and of other flinty organisms) by waters percolating through sediments in course of formation, we find a sufficient source for supplying the amorphous and gelat- inous silica of the chalk-flints. A similar origin may with all probability be ascribed to at least some of the chert- nodules so common in many formations. As regards the classification of the Siliceous Sponges, natu- ralists now universally accept the division of the group into the two primary sections of the Hexactinellidce and Litliistidce, first proposed by Oscar Schmidt, and subsequently very variously subdivided by different authorities. It is not necessary to consider the minor subdivisions here, but we may define the two primary sections above named, and glance at some of the leading types of each, taking these in geological rather than zoological order. (A.) Section Hexactinellidce. Siliceous Sponges, the fun- damental elements in the skeleton of which are six -rayed spicides, the rays of ivhich are almost invariably at right angles to each other. In the centre of each spicule is an axial canal, consisting of three tubes cutting each other at right angles. The spicules may be only united by sarcode, or they may be fused together by amorphous silica, in either case being so disposed as to form a trellis- work (fig. 38, B) with rectangular or polyhedral meshes. Besides the true " skeleton-spicules," the sarcode contains (in the living forms at any rate) numerous detached " flesh-spicules," which are also fundamentally six-armed, but which give off secondary branches, so as to form a " rosette." Until of late years, even the living Hexactinellidce were very little known, the most familiar example of the group SPONGIDA. 143 being the beautiful Venus's Flower-basket (Euplectella). Now we not only know of a long series of living Sponges with a flinty skeleton built upon the plan above defined, but we Fig. 38. A, Side-view of a specimen of Cceloptychium Seebachi, of the natural size, from the Cretaceous formation ; B, Portion of the hexradiate skeleton of the same, enlarged 65 times. (After Zittel.) know that the group enjoyed a great development in past time, and that it can be traced back to the Silurian period. All the recent Hexactinellidce are inhabitants of the more profound depths of the ocean, and are in no case strictly shallow-water forms. It is probable, therefore, that the fossil 144 PROTOZOA. Fig. 39. Section of Astylospov yia prcemorsa, a siliceous Silurian Sponge. (After Roemer.) forms indicate that the deposits in which they occur were laid down in a considerable depth of water. Of the Silurian Sponges, the only forms which have been definitely shown to be Hexactinellids are Astylospongia (fig. 39), Palceomanon, and ProtacJiilleum. In the first of these, we have small, more or less globular, unattached sponges, furnished with a cup-shaped or funnel-shaped depression at the summit. The aquiferous canals are partly radial and directed from the surface towards the centre, and partly radial but vertically disposed parallel to the surface, so as to open in the summit-cup. The skeleton consists of hexradiate spicules, which are soldered together so as to form a continuous net- work, the points of intersection of the component rays of each spicule (the so-called " crossing-nodes " ) being solid. Palceomanon is basin-shaped, and with larger lateral canals, but it is hardly generically separable from Astylospongia, and both occur in the Upper Silurian, the latter being also found in the Lower Silurian. In Protachilleum, the sponge- body is mushroom-shaped and stalked, and there is no sum- mit-cavity. Very little, indeed, is as yet known as to Devonian Hexac- tinellids the supposed Devonian Sponge described by McCoy under the name of Steganodictyum having been shown to be really the buckler of a Pteraspidian fish. Our knowledge of the Carboniferous representatives of this group is also singu- larly defective ; but we have the extremely interesting fact that the deposits of this age contain, in no inconsiderable numbers, the remains of ancient members of the now living genus Hyalonema. In this genus, comprising the so- called " Glass-rope Zoophytes," there is a comparatively small sponge-body, rooted to the mud of the sea-bottom by a longer or shorter rope of delicate siliceous fibres. In addition to SPONGIDA. 145 this skein of " anchoring fibres," there are branched spicules, which are four-armed or five-armed in the recent forms, but some of which in the fossil forms are hexradiate. A Car- boniferous species has been described as Hycdonema Smitliii ; and its " rope " was long known to palaeontologists under McCoy's title of Serpula parallela, being supposed to be formed of the parallel tubes of one of the Tubicolous Annelides. The root -fibres of Hyalonema Smithii are of large size, with a minute central canal, and terminating in anchoring booklets, their sides being smooth. Silurian species of Hyalonema, still undescribed, are also known to occur. Nothing is at present known of Permian Hexactinellids (unless we refer here the imperfectly examined Bothroconis Fig. 40. Portion of the skeleton of Tremadictyon reticulatitm, enlarged 50 diameters, from the Jurassic (after Zittel). The original spicules are soldered into a continuous trellis-work by a coating of silica ; but their position and hexradiate form is shown by their axial canals. The " crossing-nodes," or points of intersection of the arms of each spicule, are solid. of King). No members of the group, also, have been hitherto detected in the Trias, and they are scarce or wanting in the lower portion of the Jurassic series. In the Tipper Jurassic, however, we meet with a great number of Hexactinellid Sponges. Of these, Craticularia, Verru- cocodia, Tremadictyon (fig. 40), Sporadopyle, and Sphenaulax, possess a skeleton built upon the same type as the living VOL. I. K 146 PROTOZOA. Eurete and Farrea ; Pacliyteicliisma and Trocliobolus are early forms of the great family of the Ventriculitidce ; Cypellia, Stauroderma, and others represent the extinct family of the Staurodermidce ; and Stauractinella belongs to the group of Hexactinellids in which the skeleton-spicules are only united by sarcode, so that they do not form a continuous network. In the Cretaceous deposits, and especially in the Chalk itself, the Hexactinellids are very largely and abundantly represented. Of the family of the Euretidce we have now few forms (Craticidaria, Verrucoccelia, &c.) ; but the great family of the Ventriciditidce (employing this term here in a general sense for the groups allied to the Ventriculitidw proper) undergoes a marvellous expansion. The shape of the sponge - body in this family is very variable, but is usually more or less cup-shaped, infundibuliform, or cylindrical, the wall being often folded (fig. 41). The spicules of the skeleton are always united into a continuous lattice- work, and their " crossing- nodes " are not solid. On the other hand, the point of inter- section of the arms of each hex- radiate spicule forms an open octahedron, in the centre of which the central canals of the six rays form a delicate axial cross. The boundaries of the central space are formed by twelve oblique uniting beams, the whole forrn- ing an elegant octahedron, which is known as the " lantern " (see fig. 38, B). The most import- ant of the Cretaceous genera of the Ventriculitidce using the term in the above wide sense are Ventriciditcs (fig. 41), Ccphalites, Cceloptychium, Ccdlodictyon, Marshallia, Pleurope, Plocoscyphia, Etheridgia, Oamerospongia (fig. 42), and Tremabolites. Very few Tertiary representatives of the Ventriculitidce have hitherto been Fig. 41.- Ventriculites simplex. White Chalk, Britain. SPONGIDA. 147 discovered, but the family survives in the existing genus Myliusia. Of the remaining Cretaceous Hexactinellits, we may just mention Coscinopora (fig. 43), with its cup-sharad skeleton affixed to foreign bodies by ramified roots, Fig. 42. Camerospongia fung iformis. Cretaceous. lattice-work of the skeleton is irregular, and the nodes of the spicules are partly solid, and partly furnished with a " lantern." In the nearly allied Guettardia the wall is deeply folded in a stellate manner, and the crossing- nodes are solid. Lastly, we find in the Cretaceous the first representative of the cu- rious modern genus Aphro- callistcs. In the Tertiary period comparatively few Hexac- tinellids make their appear- ance, doubtless owing to the fact that so many of the of this ao-P arp Fig ' 4:i> - Coscin P ra wpuUJurm is, and a por- shallow -water deposits. In the Miocene of Oran, in North tion of its surface enlarged. Cretaceous. Africa, however, an abun- dance of Hexactinellids (Craticularia, Aphrocallistes, &c.) have been detected. At the present day, we find an abundance of Hexacti- nellid Sponges, of which the most striking forms are the ex- clusively recent Euplectellidce, in which the skeleton-spicules are cemented together into a ladder-like trellis-work, and there is a single " osculum " provided with a porous lid. (B.) Section Lithistidcc. In this group are comprised Siliceous Sponges in which the spicules are fundamentally quadriradiate, three of the four arms being so disposed as to 148 PROTOZOA. come together at an angle of 120, their extremities being divided into processes by means of which contiguous spicules interlock with one another ; while the fourth arm lies in a different plane and forms a cylindrical shaft from which the other three spring. The spicules are not united by a siliceous cement ; but by the interlocking of their ends the skeleton forms a more or less continuous framework, the meshes of which are more or less irregular and curvilinear. In the recent species " flesh-spicules " are also present. The fossil Litliistidce 1 have not yet been so extensively worked out, as is the case with the fossil Hexactinellids ; but they are said by Zittel to be represented in the Silurian (Aidocopium, Calatliium (?), and Eo- spongia (?)). The same observer has likewise indicated their abundant occurrence in the Jurassic period ; but it is not till we reach the Cretaceous period that we are confronted with the maximum development of this group. Of the Cretaceous Lithistids, by far the most important is the familiar and widely distrib- uted genus Siphonia, the structure of which has been investigated by Mr Sollas. In this genus the sponge-body consists of a variably- shaped head, supported upon a longer or shorter stem, and attached thereby to some foreign body (fig. 44), but the stem may be wanting, when the sponge is attached by diverging root -fibres. The exhalant water- canals open at the summit of the sponge, usua iiy by oscula situated within a cup- J f shaped apical cavity, w T hile the inhalant canals open by " pores " on the lateral sur- faces. The skeleton - spicules (fig. 45, B) are furnished with three diverging arms, are bifurcated, and furnished 1 Since the above was written, Professor Zittel has published a detailed memoir on the Lithistidce (N"eues Jahrbuch fur Mineralogie, &c., 1878), in which this difficult group is systematically worked out. The general results above stated are, however, not affected by this, though our knowledge of the fossil forms is immensely increased. Fig. 44 - ficus, a Cretaceous sponge. SPONGIDA. 149 with tubercles and intervening depressions, by means of which they are interlocked into a rigid framework. The agreement in shape between the skeleton -spicules of Si- phonia, and those of the living Lithistid genus Discodermia (fig. 45, A), is so close, as shown by Mr Sollas, that it will Fig. 45. A, A single skeletoii-spicule of the living Lithistid Discodermia polydiscits, magni- fied 60 diameters ; B, Small portion of the skeleton of Siphonia pyriformis, similarly enlarged. (After Sollas.) be perhaps with difficulty that the latter can be retained as generically distinct from the Cretaceous type. Other well-known Cretaceous Lithistids belong to the genera Che- nendopora, Jerea, Chonella, Verruculina, Astrocladia, Amphi- thelion, &c. In the Tertiary period, lastly, numerous Lithistid Sponges have been detected, but none of these are sufficiently important to demand special consideration. 150 PROTOZOA. LITERATURE. [In the following brief bibliography of works which may advan- tageously be consulted by the student of the fossil Protozoa, as in all subsequent lists of a similar nature, it is hardly necessary to say that only a very limited number of the most important and easily accessible treatises and memoirs have been selected for mention.] FORAMINIFERA. 1. " Introduction to the Study of the Foraminifera." ('Ray Society.') 1862. Carpenter. 2. " Carboniferous and Permian Foraminifera " (with a general Intro- duction). ' Monographs of the Palseontographical Society,' 1876. H. B. Brady. 3. " Handbuch der Palseontologie," vol. i. pp. 61-114, 1876. Zittel. 4. " Mikrogeologie." Ehrenberg. 1854. 5. " Foraminiieres Fossiles du Bassin Tertiaire de Vienne." D'Or- bigny. 6. " Entwurf einer Systematischen Zusammenstellung der Forami- niferen." ' Sitzungsber. d. K. Akad. Wiss. Wien,' 1861. Reuss. 7. " Monograph of the Foraminifera of the Crag," 1868. Rupert Jones, Parker, and Brady. 8. " Beitrage zur Kenntniss der Organisation und Systematischen Stellung von Receptaculites." C. W. Giimbel. 'Abhandl. der K. Bayerischen Akad. der Wiss.' Bd. XII. 1876. 9. " Die Sogenannten Nulliporen " (Lithothamnium und Dactylo- pora). Zweiter Theil. * Abhandl. der K. Bayerischen Akad. der Wiss.' Bd. XI. 1874. 10. The Dawn of Life.' J. W. Dawson. 1876. 11. "On the Occurrence of Organic Remains in the Laurentian Rocks of Canada." Sir W. E. Logan. ' Quart. Journ. Geol. Soc.,' xxi. 45-50. 1865. 12. "On the Structure of Certain Organic Remains in the Laurentian Limestones of Canada." J. W. Dawson. ' Quart. Journ. Geol. Soc.,' xxi. 51-59. 1865. 13. "Additional Note on the Structure and Affinities of Eozoon Canadense." W. B. Carpenter. * Quart. Journ. Geol. Soc.,' xxi. 59-66. 1865. 14. " Supplemental Note on the Structure and Affinities of Eozoon Canadense." W. B. Carpenter. ' Quart. Journ. Geol. Soc.,' xxii. 219-228. 1866. 15. " On the So-Called Eozoonal Rock." King & Rowney. ' Quart. Journ. Geol. Soc.,' xxii. 185-218. 1866. SPOXGIDA. 151 RADIOLARIA. 16. " Mikrogeologie," 1 854. Ehrenberg. 17. "Die Radiolarien," 1862. Haeckel. 18. "Fortsetzung der Mikrogeologischen Studien," &c. ' Abhandl. d. K. Akacl. Berlin,' 1875. Ehrenberg. 19. " Handbuch der Palseontologie," 1877. Zittel. SPONGIDA. 20. " Grundziige einer Spongien-fauna der Atlantischen Gebietes," 1876. Oscar Schmidt. 21. " Die Kalk-Schwamme." Hseckel. 1872. 22. " Anatomy and Classification of Sponges." ' Annals of Nat. Hist./ 1875. Carter. 23. "Vitreous Sponges." 'Annals Nat. Hist./ 1868. Wyville Thomson. 24. " Ventriculitidse of the Chalk." 'Annals Nat. Hist./ 1847-48. Toulmin Smith. 25. "Beitrage zur Systematik der Fossilen Spongien." ' Neues Jahrbuch fur Mineralogie,' &c., 1877. Karl Zittel. (Trans, in 'Ann. Nat. Hist./ 1877.) 26. " Ueber Coeloptychiurn. Ein Beitrag zur Kenntniss der Organ- isation Fossilen Spongien." ' Abhandl. der K. Bayerischen Akad. der Wiss.' Bd. XII. 1876. Karl Zittel. 27. " Die Spongitarien des Nord-deutschen Kreide-gebirges." * Pal- seontographica/ 1864. F. A. Roemer. 28. " Palceontologie de la Province d'Oran. 5th Fasc. Spongiaires/' 1872. Pomel. 29. "On the Hexactinellidse and Lithistidse." 'Ann. Nat. Hist./ 1873. Carter. 30. "On a Carboniferous Hyalonema." 'Ann. Nat. Hist.,' 1877. Prof. Young and Mr John Young. 31. " Structure and Affinities of the Genus Siphonia." 'Quart. Journ. Geol. Soc.' Vol. XXXIII. 1877. Sollas. " On Cliona." ' Ann. Nat. Hist./ 1849. Albany Hancock. " On the Minute Structure of Stromatopora and its Allies." ' Proc. Linn. Soc./ 1878. Nicholson and Murie. 34. " Ueber die Natur der Stromatoporen," 1867. Von Rosen. 35. " Ideen iiber die Verwandschaftsverhaltnisse der Hexactinelliden." ' Zeitschr. fur Wiss. Zool.,' 1876. Marshall. 36. "Studies on Fossil Sponges" (Lithistidse). Karl Zittel. 'Ann. and Mag. Nat. Hist.,' Ser. V. Vol. II. 1878. (Trans, by W. S. Dallas from ' Abhandl. d. K. Bayer. Akad. der Wiss.' Bd. XIII. 1878.) 152 CHAPTER IX. SUB-KINGDOM 1I.CCELENTERATA, FOSSIL HYDROZOA. THE sub-kingdom Ccelenterata (Frey and Leuckhart) may be considered as a modern representative of the Radiata of Cuvier. From the Radiata, however, the Echinodermata and Scolecida have been removed to form the Anmdoida, the entire sub-kingdom of the Protozoa has been taken away, and the Polyzoa have been relegated to their proper place amongst the Mollusca. Deducting these groups from the old Radiata, the residue, comprising most of the animals commonly known as Polypes or Zoophytes, remains to constitute the modern Ccelenterata. The Ccelenterata may be defined as animals whose alimentary canal communicates freely with the general cavity of the Itody (" somatic cavity "). The substance of the body is made up of two fundamental membranes an outer layer, called the " ecto- derm," and an inner layer, or " endoderm." Peculiar urticating organs, or " thread-cells',' are usually present ; and, generally speaking, a radiate condition of the organs is perceptible, espe- cially in the tentacles with which most are provided. In all the Ccelenterata distinct reproductive organs have been shown to exist. The sub-kingdom Ccelenterata is divided into the two great classes of the Hydrozoa and Actinozoa, and the following- table indicates the characters and principal subdivisions of these : FOSSIL HYDROZOA. 153 TABLE OF THE DIVISIONS OF THE CCELENTERATA. CLASS A. HYDROZOA. The walls of the digestive sac not separated from those of the general body-cavity, the two coinciding with one another. Reproductive organs in the form of external processes of the body- wall. Sub-class I. HYDROIDA (Hydroid Zoophytes). Order 1. Hydrida.Ex. Hydra. Order 2. Corynida. Ex. Tnbularia. Order 3. Thecaphora. Ex. Sertularia, Campanularia. Order 4. Thecomedusce. Ex. Stephanoscyphus. Sub class II. SIPHONOPHORA (Oceanic Hydrozoa). Order 5. Calycophoridce. Ex. Diphyes. Order 6. Physophoridce. Ex. Physalia. Sub-class III. DISCOPHORA (Jelly-Hshes). Order 7. Medusidce. Ex. vEgina. Sub-class IV. LUCERNARIDA (Sea-blubbers). Order 8. Lucernariadce.Ex. Lucernaria. Order 9. Pelagidce. Ex. Pelagia. Older 10. Rhizostomidce. Ex. Rhizostoma. Sub-class V. GRAPTOLITID.E (Graptolites). Sub-class VI. HYDROCORALLIN^E. Ex. Millepora, Stylaster. CLASS B. ACTINOZOA. Animal with a differentiated digestive sac opening below into the body-cavity, but separated from it by an inter- vening " perivisceral space," which is divided into compartments by a series of radiating vertical partitions or " mesenteries," to the faces of which the reproductive organs are attached. Order 1. Zoantharia. Ex. Sea - anemones, Star - corals, Brain- corals. Order 2. Alcyonaria. Ex. Sea-pens, Fan-corals, Sea-shrubs, Red- coral, Heliopora, Heliolites. Order 3. Rugosa. Ex. Cyatl.ophyllum. Order 4. Ctenophora. Ex. Venus's Girdle. With the exception of one or two Graptolites (Dendro- f/raptus), which are known in the Upper Cambrian, the Ccelenterata are first well represented in the Lower Silurian ; and when we consider that we find the two great classes thoroughly differentiated, and existing under many and varied types, at this early period, we are forced to conclude that the first appearance of the sub-kingdom must really have been at a much more ancient epoch. The Crelenterates are extremely abundant and important as fossils, some large groups being wholly or largely unrepresented at the present day ; but owing to the fact that other large groups (such as 154 CXELENTERATA. the Luccrnarida, the Oceanic Hydrozoa, and the Ctenophora] are almost or quite without hard parts, and therefore only capable of preservation in the fossil condition under very exceptional circumstances, the geological history of the sub- kingdom is very imperfect. FOSSIL HYDROZOA. Of the living orders of Hydrozoa, the Fresh-water Polypes (Hydrida) and the Oceanic Hydrozoa (Calycophoridce and Physophoridw) have left no traces of their former presence, as might have been anticipated from their want of hard structures. The order of the Medusidce and the sub-class Lucernarida (Jelly - fishes and Sea - blubbers) are equally destitute of hard parts, and their absence from the palse- ontological record might have been confidently predicted. Curiously enough, however, traces of both groups have been detected in the fine-grained lithographic slates of Solenhofen, Pappenheim, and Eichstadt. Of the Medusidce, the two living families of the ^Eyuoridce and Trachynemidce have been recognised by their impressions ; and an ancient member of the order Ehizostomidce^ (Hexarhizites) represents the Lucernarida in the same formation. With these excep- tions, however, the only living orders of Hydrozoa which have fossil representatives are the Corynida and Thecaphora, both of which possess a chitinous or horny integumentary skeleton. In neither case, however, can the evidence be said to be w T holly free from suspicion, except in the instance of Hydractinia and its immediate allies. I. CORYNIDA or TUBULARIDA (Pipe -corallines). Animal simple, consisting of a single polypite ; or compound, consisting of several polypites united to one another by a common flesli or ccenosarc. The ccenosarc generally secretes a hard chitinous outer covering or " polypary ;" but the separate polypites are never protected by cup-like expansions of the polypary. As a rule, the polypary extends only to the bases of the polypites (fig. 46, A) ; but in one case it is continued far enough up- wards to include the bases of the tentacles (fig. 46, B). Generally the polypary is more or less plant-like, and is FOSSIL HYDROZOA. 155 attached to some foreign body by its base ; sometimes it forms a crust-like investment to shells (Hydradinia) ; some- Fig. 46. Recent Corynida. A, Portion of the colony of J'erigonimus minulus, with poly- ]>ites and reproductive buds, enlarged about 25 diameters ; B, A single polypite of Bimeria rcstita, greatly enlarged, showing the extension of the polypary upon the bases of the tentacles. (After Allman.) times it is rooted in the sand of the sea-bottom. Usually the polypary is horny in texture, but forms of Hydractinia 156 CCELENTER ATA. with a calcareous polypary have been described by Mr Carter. The most important genus of Corynida which has been certainly detected in the fossil condition is Hydractinia, which is still represented by living species. The recent Hydractinia\ as a rule, are horny as regards the texture of the skeleton, and form crusts attached to the outer surface of shells. By age, these crusts come to be composed of successive close-set, vertically superimposed laminae, and the shell upon which they originally grew is commonly more or less dissolved away and replaced by the substance of the parasite. In an African Hydractinia, described by Mr Carter, the skeleton is calcareous, but not essentially different to the horny forms in minute structure. Several fossil forms of Hydractinia are now known, two of them (H. cretacca and H. Vicaryi) being from the Upper Cretaceous system. Of these ancient types, the latter is described as being siliceous, but it is more prob- able that its skeleton was originally calcareous, and that it has been silicified. In the Miocene Tertiary another species occurs ; and in the Pliocene (Coralline Crag of Suffolk) we have another species, in which the skeleton is calcareous, Mr Carter's discovery of a living calcareous Hydractinia rendering it probable that the fossil form possessed a skeleton primitively composed of carbonate of lime. The genera Thalaminia (Jurassic and Cretaceous) and Sphceractinia (Jurassic) have been founded by Steinrnann for forms sup- posed to be allied to Hydractinia. According to Mr Carter, the fossils which have been usually described under the name of Strcmatopora (see p. 137), together with the large arenaceous Foraminifera described by Dr Carpenter under the title of Parkeria, are really closely related to Hydractinia, and are truly fossil Hydrozoa. So far as Stromatopora and its allies are concerned, the author is unable at present to accept this view, which appears to be founded upon resemblances of analogy rather than of real and fundamental likeness. It is not impossible, however, that Lindstrom is correct in regarding the Silurian genus Labechia which has generally been regarded as a coral as a close ally of Hydractinia. In this ancient and singular type we have flattened calcareous expansions (fig. 47), the upper surface of which is studded by blunt spines. These spines are seen in vertical sections (fig. 47, c), to be the summits of perpendicular pillars, the spaces be- tween which are occupied by vesicular calcareous plates. The chief FOSSIL HYDROZOA. 157 points in which Labechia differs from Hydractinia are the apparent absence of any apertures on the surface, and the fact that the former does not grow in the form of crusts enveloping shells, but in the shape of expansions attached to a foreign body at one point only. Two other fossil genera, viz., Palceocoryne and Corynoides, have been referred to the Corynida, but in neither case is the reference free from doubt. Palceocoryne (fig. 48) is a minute organism which was discovered by Dr Martin Duncan and Mr Jenkins growing attached to the margins of Lace- corals (Fenestcllce) in the Carboniferous rocks of Scotland. Fig. 47. Labechia conferta, Edw. & H. A, A small specimen, of the natural size. B, A piece of the upper surface of the same, enlarged, c, Portion of a vertical section under a low microscopic power : a, The calcareous columns, represented as opaque ; b, The vesicular tabulae, filled up with calcite. Its base is expanded, with finger -like processes of .attach- ment. From 'the base rises a short robust stem, which is marked with flutings and superficial granulations. The stem terminates in a single polypite, the mouth of which is sur- rounded by a single whorl of slender processes or " tentacles," in the centre of which is the mouth. The entire polypary, as above described, is " calcareous, dense, and ornamented." In one living form only (viz., Bimeria, fig. 46, B), is the polypary continued along the tentacles and upper part of the body of the polypite, and in this case the polypary is simply of the consistence of parchment. This peculiarity, therefore, with the possession of a calcareous polypary, renders the reference of Palceocoryne to the Corynida a matter of question. According to the views of Prof. Young and Mr 158 CCELENTERATA. John Young, indeed, the fossils known as Palccocoryne are really peculiar processes belonging to the Polyzoon (Fenestella) upon which they grow. Fig 48. Palceocoryne radiatum, enlarged fifteen diameters. (After Duncan and Jenkins.) The genus Corynoides was proposed by the author for some singular fossils from the Lower Silurian rocks of Scotland. Each consists of a cylindrical corneous tube (fig. 49), tapering towards the base, where it is furnished with two small spines, and expanding above into a species of toothed cup. Corynoides consists of a single polypite, and in this respect may be compared with some living Corynida. It would seem, however, not to have been attached to any foreign body as all living Corynids are and its true affinities are thus rendered uncertain. II. THECAPHOIJA. (or Sertularida and Campanularida). Animal compound, rooted and plant-like, consisting of mimer- Fig. 49. Corynoides call cuhiris, enlarged. (Origi nal) FOSSIL HYDROZOA. 159 ous poli/pites united by common flesh or ccenosarc. The cceno- sarc is more or less branched (fig. 50, a), and secretes a strong chitinous investment or " polypary." The polypites are also protected within " hydrothecw," or little cup -like expansions derived from the polypary. The pi^ocess of reproduction is carried on by the development of the reproductive dements irithin horny urn - like sacs, which are of larger size than tlu' " hydrotheca? " and are 'known as "ovarian capsules" or " gonothccm " (often called " gonophores "). Type of the order the Sea-fir (Sertularia, fig. 50). Fig 50. o, Sertulariu (Diphasia) pinnnta, natural size ; , Fragment of the same enlarged, carrying a male capsule (o), and showing the hydrothecse (A); b, Fragment of Campanularia neglecki (after Hincks), showing the polypites contained in their hydrothecse (A), and also the point at which the ccenosarc communicates with the stomach of the polypite (o). There is considerable uncertainty as to the existence of any fossil representatives of this order. No undoubted Sertularian, at any rate, is as yet known to the palaeontol- ogist ; but there are several genera which may with more or less probability be referred to this place. The most im- portant of these as being those in which the reference is probably correct are certain forms usually referred to the (,'riijttolitida:, of which the genera Dendrograptus and Dicty- onema may be noticed in particular. The forms referred to Dendrograptus are exclusively confined to the Upper Cam- brian and Lower Silurian formations. They consist of plant- 160 GCELBNTERATA. like spreading and branched growths, which are furnished with a strong footstalk (fig. 51). In all probability the organism was attached by the base of the footstalk to some foreign body, but no actual demonstration of this has as yet been obtained. The branchlets carry upon one side a series of little chitinous cups or " cellules," each of which must have contained a polypite, and which agree with the similar struc- Fig. 51. Dcndrog raptus Hallianus. a, Portion of the frond, natural size ; b, Portion of a branch, enlarged ; c, The footstalk and some of the principal branches, natural size. (After Hall.) tures of ttte Graptolites in partially overlapping one another ; thus differing from the " hydrotheceB " of the Sertularians. In Dictyonema (fig. 52) we have ' organisms resembling Dendrograptus in many respects, but not possessing any foot- stalk. The frond is branched and plant-like, and is fan- shaped or funnel-shaped in form. It is not certainly known whether the organism was attached by its base or not ; but there is the strongest probability in favour of its having been fixed. The branches radiate from the base, running nearly parallel with one another, and often bifurcating. They are united to one another at short intervals by numerous, irregular, slender, transverse processes or dissepiments, and they bear small horny cups or " cellules " like those of the FOSSIL HYDROZOA. 161 Graptolites. Dictyonema ranges from the Upper Cambrian to the Middle Devonian. The genus bears a close superficial resemblance to the Fenestellce or Lace-corals (belonging to the Polyzoa) ; but the latter have a calcareous skeleton, and have no "cellules." Besides the above-mentioned genera, Callo- graptus and Ptilograptus may with great probability be referred to the Sertularida ; as may, perhaps, be the obscure Fig. 52. Dictyonema retiforme, Hall. (After Hall.) fossils Buthograptus and Tliamnograptus. All these genera are Silurian in age. OLDHAMIA. The singular fossils described under the genus Oldhamia may be noticed here, as they have been referred to the Hydrozoa ; though their true nature is altogether un- certain. Oldhamia occurs in certain green and purple grits of Lower Cambrian age, at Bray Head, in Wicklow, Ireland, where the fronds are found in great abundance, matted together, and spreading over the surfaces of the strata. A species of Oldhamia is also said to occur plentifully in the Potsdam Sandstone (Upper Cambrian) of Wisconsin, in North America. Oldhamia antiqua, the commonest species, consists of a central thread-like axis from which spring bundles or umbels of short radiating branches (fig. 53), at regular in- VOL. I. L 162 CCELENTERATA. tervals. Each branch " is formed of a series of articulations marking the position of minute cells" (E. Forbes). Old- hamia has been variously referred to the Sertularian Zoo- phytes, to the Polyzoa, and to the vegetable kingdom. The most probable conjecture, perhaps, would refer the genus to the calcareous sea-weeds (Salter). III. SUB -CLASS GRAPTOLITIM (Graptolites EHABDO- PHORA, Allman). The Graptolites form a very large and important family of fossils which usually present themselves in the shape of horny linear bodies, toothed or serrated upon one or both sides, and often combined into more or less complex sys- tems. If we disregard the genus Dictyonema, which is best referred elsewhere, the Grapto- lites have an extremely definite range in point of time, being exclusively confined to the Silu- rian deposits. They attain their maximum of development in the basement - beds of the Silurian (Quebec group of Canada and Skiddaw Slates of England), are abundantly represented in the higher portion of the Lower Silurian, and die out altogether before the close of the Upper Silurian period. Excluding the genera Dictyonema, Dendrograptus, Ptilograp- tus, and Callograptus, the Grraptolitidce may be defined by the possession of a compound polypary, consisting of a tubular chitinous investment enclosing the coenosarc, giving origin to numerous cup - like " cellules " or " hydrothecse," each of which protected a polypite. The polypary was free, and was not attached to any foreign body ; and the poly- pites were not separated from the coenosarc by any par- tition. Lastly, the polypary was almost always strength- ened by a chitinous rod or fibre, which is termed the " solid axis," and which is analogous to the chitinous rod Fig. 53. Oldhamia antiqim, natural size (after Salter). Cambrian. FOSSIL HYDROZOA. 163 described by Dr Allman in the singular Polyzoon, EJidbdo- pleura. From the above definition, it will be seen that the Grapto- lites agree with the living Sertularians in possessing a cor- neous polypary, which not only invests the ccenosarc, but is expanded into little cups or " hydrothecae," within which each polypite is protected. The Graptolites, however, differ from the Sertularians in the fact that the polypary was unattached, and apparently free-floating, whilst it has not, except in a few cases, anything like the plant-like appear- ance of the latter. Further, the hydrothecse of the Grapto- lites, except in the genus Rastrites, always more or less overlap one another; whereas those of the Ser- tularians are not in contact. Lastly, no Sertularian exhibits any structure which can be compared with the " solid axis " of the Graptolites. Taking such a simple Graptolite as Monograptus priodon (fig. 54), or M. Sagittarius (fig. 55, A), as the type of the sub-class, the polypary is seen to consist of three elements, which are known as the " solid axis," the " common canal," and the " cell- ules." The " solid axis " is a cylin- drical fibrous rod which gives support to the corneous and flexible polypary. The term " solid " is probably a mis- nnrnpr fnr it waa alrnnat novtoiTilir , was almost certainly hollow, and filled With living mate- . rial. It appears to be absent in Retiolites Geinitzianus, but some un- certainty rests upon this point. As a very general rule, it is prolonged as a longer or shorter naked rod beyond one or both ends of the poly- pary, and either extension may be more or less dilated. Its basal prolongation, with or without an accompanying exten- Fig. 54. Morphology of Mono- graptus priodon. A., Monograptus priodon, Bronn, preserved in relief lateral view slightly enlarged; B, Dorsal view of a fragment of the same species considerably enlarged ; c, Front view of a fragment of the same, showing the mouths of the cellules much enlarged ; D, Transverse section of the same. All from the base of the Coniston Flags. (Original.) 164 CCELENTERATA. sion of the common canal, is termed the " radicle/' or " initial point," as marking the organic base of the frond. The " common canal " is the tube in which the coenosarc was enclosed ; but it commonly appears, in compressed speci- mens, merely as a vacant space between the " cellules " and the solid axis. The common canal gives origin, by a process of budding, to the " cellules " or " hydrothecse," which are little horny cups for the reception of the polypites. Each Fig. 55. A, Young individual of Monograptus Sagittarius, His., showing the slender curved base of the frond, and the extension of the axis beyond its opposite end ; B, Base of another individual of the same, in which there is an extremely long "radicle;" c, Frag- ment of M. Sagittarius, much enlarged to show the cellules from a specimen in relief; D, Specimen of Monograptus Clingani, Carr., showing the distal and proximal extensions of the axis. cellule rests by its base upon the common canal, is separated from its neighbours by " cell-partitions/' and opens at its apex by a distinct aperture or " cell-mouth," through which the polypite could exsert its tentaculate head. The reproductive process appears, in some cases at any rate, to have been carried on by the formation at certain seasons of horny capsules, of much greater size than the cellules, within which the generative elements were matured. In some cases these " ovarian vesicles " have been found actually attached to the fronds of Graptolites. In other cases, as described by the writer, we find numerous bell- shaped horny capsules, termed " Daivsonice" (fig. 56), each with a little spine at its summit, scattered through the rock FOSSIL HYDKOZOA. 165 in which the Graptolites occur, but only doubtfully attached to the fronds of the latter. These we may infer to have been " ovarian vesicles ; " but they differ from the bodies so called in the Sertularians in becoming detached from the parent colony. Fig. 56. Supposed " ovarian capsules " or reproductive buds of Graptolites. As regards the affinities of the Graptolites, opinions widely differ, though the view now generally adopted by palaeontologists is that they constitute an aberrant and ancient type of the Hydrozoa. In the actual structure of the polypary, as is easily seen by a comparison with the B c Fig. 57. A, A fragment of Plumularia pentuitula, magnified, showing a single row of hydro- thee* ; B, A fragment of Sertularia fallax, magnified, showing a double row of hydrothecse ; c, Fragment of Sertularia fallax, magnified, showing an ovarian capsule. (After Johnston.) subjoined illustration (fig. 57), representing, on an enlarged scale, the shape and arrangement of the hydrothecae among the Sertularida, the Graptolites certainly closely approach the recent Sea-firs, though the latter possess no " solid axis," and the hydrothecse do not overlap, while the polypary is always fixed. In the unquestionable fact, also, that the 166 CCELENTERATA. reproductive elements in some Graptolites (if not in all) are matured in special chitinous receptacles, we have an undoubted approach to the Sertularians, with their " ovarian capsules " (fig. 57, c). By Professor Allman, our highest living authority on the Hydrozoa, the Graptolites are regarded as referable to the sub -kingdom of the Hydrozoa, but as presenting us with an ancient and degraded type of this class, in which the hydrothecse were occupied simply by mobile amoeboid proto- plasm, instead of by fully-developed polypites constructed upon the Cce- lenterate type. If, namely, we look at the living Plumularians among the Sertularida, we find that the poly- pary, in addition to the ordinary hydrothecse, with their contained polypites, carries a number of cup- shaped processes, which are known as " nematophores " (fig. 58, n). Each of these cup-like appendages is filled with protoplasmic matter, which has the power of emitting amoeboid pro- longations or filaments, strictly com- parable to the " pseudopodia " of the Rhizopods. Upon Dr Allman's view, the " cellules " of the Graptolites were similarly occupied by amoeboid protoplasm, so that these extinct or- ganisms might be compared with Plumularians in which the colony produced nothing but "nemato- phores," and in which the ordinary polypites had not been developed. In the absence of direct evidence, this view can, however, only be re- garded as a more or less probable hypothesis. On the other hand, there are not wanting points of relationship between the Graptolites and some of the Polyzoa, and especially those members of the latter class in which (as in Vesicularia and its allies) the cells of the colony communicate by means of a common tube. A further point of affinity between these two groups of organisms is established by the presence in Ehdbdopleura an unquestionable marine Polyzoon of a hollow chit- inous axial tube, which may in many respects be compared with the " solid axis " of the Graptolites. In other points, however, Rhabdopleura is entirely unlike any known Graptolite, and especially so in its general form, and in the fact that it is fixed to solid bodies ; and, upon the whole, Fig. 58. Portion of a branch of Anten- nularia antennina, enlarged (after Allman). p, One of the polypites ; n, n, n, Ne- matophores emitting pseudopodial fila- ments of sarcode; n', Nematophore with its sarcodie contents quiescent ; c, Coeno- sarc enclosed within the polypary. FOSSIL HYDROZOA. 167 the balance of evidence is unquestionably in favour of a reference of the Graptolitidce to the Hydrozoa. Fig. 59. Didymograptus V-fractus. Lower Silurian (Skiddaw Slates). Two leading types may be distinguished amongst the Graptolites, which are termed respectively " monoprionidian " and " diprionidian." The monoprionidian Graptolites, such as Monograptus priodon (fig. 54), are distinguished by the fact that the polypary, whether simple or branched, possesses but a single row of cellules or " hydrothecse." In the diprio- nidian forms, on the other hand, as in Diplograptus (fig. 63), the polypary possesses a row of cellules on each side. It is noticeable that the diprionidian Graptolites, with hardly an exception, are confined to the Lower Silurian rocks ; whilst the monoprionidian forms range from the base of the Silurian to the summit of the Upper Silurian series. Numerous genera of Grap- tolites, as here restricted, are know T n to science ; but it will be sufficient to give the diagnostic characters of a few of the commonest and more important types. In the genus Monograptus (figs. 54, 55), the polypary is simple, linear, possessing but a single row of cellules on one side, and commencing by an atten- uated, usually curved, base. Species of this genus are found from near the base of the Lower Silurian series to the very summit of the Upper Silurian deposits. In the genus Didymograptus (fig. 59), the polypary consists of two simple monoprionidian branches, which spring from a common point, which is almost invariably marked by a small spine-like " radicle." The genus attains its maximum Fig. 60. Tetragraptus quadribrachiatHii (after Hall). Lower Silurian (Skiddaw and Quebec groups). 168 CCELENTERATA. in the Quebec group of Canada and Skiddaw Slates of Eng- land, and is well represented in the succeeding portions of the Lower Silurian (Llandeilo rocks) ; but no species of the genus is known as late as the Upper Silurian period. In the genus Tetragraptus (fig. 60), the polypary consists of four simple monoprionidian branches, springing from a central non-celluliferous con- necting process, which bifur- cates at each end. The cel- luliferous branches do not subdivide, and the base may be enveloped in a peculiar corneous "disc," as will be immediately described in the genus Dichograptus. The species of Tetragraptus are exclusively confined to the Skiddaw and Quebec groups (Lower Silurian). In the genus Dichograp- tus there are more than four usually eight) simple mono- prionidian branches, which arise from the same number of divisions of a non-cellu- Fig. 6l.DichograptiisoctobracMatus, showing the central disc (after Hall). Skiddaw and Quebec groups. liferous basal process. In many cases the divisions of the basal connecting process (fig. 61), are enveloped in a species of corneous " disc " or plate, which is believed to have been composed of two laminae. The functions of this disc are doubtful ; but it has been compared with the " float " or buoy of the PJiysophoridce, an order of the Oceanic Hydrozoa. FOSSIL HYDROZOA. 169 This genus is likewise restricted to the earlier portion of the Lower Silurian period. In the genus Eastrites (fig. 62), the polypary consists of a slender axial tube, giving off on one side a series of linear tubular cellules or " hydrothecse," which are free throughout their entire length. The genus differs from all the other Graptolites, in the fact that the cellules do not overlap one another, but are free through their whole length, whilst it is not certain if a true " solid axis " is always present. In Fig. 62. Morphology of Rastrites. A, Rastrites peregrinus, Barr., from the Mudstones of the Coniston Series enlarged ; B, Rastrites capillaris, Cam, from the Upper Llandeilo Shales of Dumfriesshire enlarged ; c, Fragment of Rastrites Linncti, Barr., from the Coniston Mud- stones enlarged ; D, Fragment of R. peregrinus, greatly enlarged, showing the impressed line running up the centre of each cellule. (Original.) Britain and North America the species of fiastrites are ex- clusively confined to the Lower Silurian rocks, but in Bohemia they pass up into the lowest beds of the Upper Silurian. In the genus Diplograptus (fig. 63), the polypary consists of two simple monoprionidian stipes, firmly united to one another, back to back. The frond, therefore, is "diprioni- dian," or carries cellules on both sides. The solid axis is usually prolonged beyond the base of the polypary as a longer or shorter process or " radicle," which is often flanked by lateral spines. The solid axis is also almost invariably prolonged beyond the opposite or " distal " end of the poly- pary as a naked rod. In the nearly-allied genus Climaco- 170 CCELENTERATA. graptus, the structure is much as above described, but the cellules have such a structure that their mouths appear to be sunk below the general surface of the polypary, forming a row of rounded or quadrangular openings on each side. Both Diplograptus and Clwiaco- m graptus range in Britain and North I rL America from the base to the sum- mit of the Lower Silurian series ; but in Bohemia they rise into the lower portion of the Upper Silu- rian deposits. In the genus Dic- ranograptus the polypary is at first diprionidian, but soon splits into two monoprionidian branches which carry the cellules along their outer margins. The genus is exclusively Lower Silurian. Lastly, we may mention here the curious forms in- cluded under the generic title of Phyllograptus (fig. 64). In these forms, which are essentially charac- teristic of the lowest Silurian de- posits (Skiddaw and Quebec groups), the polypary is leaf-like in shape, and consists of four rows of cellules placed back to back, thus resem- bling two Diplograpti intersecting each other at right angles. In consequence of the peculiar struc- ture of the polypary, the Phyllo- grapti are sometimes spoken of as the " tetraprionidian " Graptolites. IV. SUB-CLASS HYDROCORALLIK&. This name has re- cently been proposed by Mr Moseley for two groups of marine animals which produce a regular skeleton of car- bonate of lime, often of large size, and which have been gen- erally referred to the Corals (Actinozoa). One of these groups comprises the well-known Millepora, (fig. 65), which is found contributing so largely to the formation of coral-reefs in the Fig. 63. A, Diplograptus pristis, His. , slightly enlarged, showing the normal condition of the base ; B, Another example of the same, slightly enlarged, showing a long radicle, and long lateral spines ; c, Another of the same, enlarged, showing lateral spines, succeeded proximally by a small bulb, but showing no true radicle. (Ori- ginal.) FOSSIL HYDROZOA. 171 West Indies and Pacific. The calcareous skeleton of Mille- pora is mostly in the form of foliaceous or laminar expan- sions, stony in texture, with a smooth surface studded with minute apertures of two sizes, the larger of these being much the fewest (fig. 65, c). The larger openings are the mouths of tubes (fig. 65, B, p, p), which are divided by transverse calcareous partitions into a number of compartments, only the most superficial of these being actually tenanted by the living animal. The smaller tubes are similarly septate or "tabulate," and the general tissue of the skeleton (fig. 65, c) is composed of calcareous trabeculae traversed by a series of ramifying and anastomos- ing coenosarcal canals, which place the tubes occupied by the zooids in direct commu- nication. 1 From the presence of trans- verse partitions, or "tabulse," its tubes, Millepora was in Fig. 64. Group of individuals of Phyllo- graptus typus, from the Quebec group of .. Canada (after Hall). One of the four rows generally placed amongst the of cells is hidden on the under surface. so-called "Tabulate Corals," with the typical forms of which it has no affinity. Though its skeleton is abundantly obtained in the regions where it occurs, the living animal has been rarely observed. The late Professor Agassiz was the first to examine Millepora in its living condition, and he was led to the conclusion that the genus was unequivocally referable to 1 As regards the living animal, Mr Moseley has shown that the colony of Millepora consists of two kinds of zooids, differing in size, in structure, and in function. The larger zooids occupy the larger tubes of the corallum, and have a mouth, surrounded by four tentacles and opening into a digestive cavity. The smaller and more numerous zooids surround the larger ones, are long and slender in form, carry numerous clavate tentacles, and are destitute of anj r mouth. They perform the functions of prehension for the colony, and supply food to the nutritive zooids. 172 CCELENTERATA. the Hydrozoa. This conclusion has been confirmed by the more recent and more complete researches of Mr Moseley. At the present day, Millepora contributes largely to the formation of coral-reefs ; but little is known of its distri- bution in past time. The genus has been detected in the Tertiaries, and allied forms (Porosphcera) occur in the Chalk. The Tertiary genus Axopora is apparently allied to Millepora, but the tubes inhabited by the larger zooids are traversed Fig. 65. A, Portion of a mass of Millepora alcicornis, of the natural size ; B, Portion of the same, cut open vertically to show the larger tabulate tubes (p, p), and the spongy coenosarcal skeleton (c, c) enlarged ; c, Small portion of the surface, enlarged to show the larger and smaller openings (p and c) inhabited by the different zooids, and the reticulated calcareous tissue of the skeleton ; D, Part of a tentacular polypite, enlarged, showing two whorls of knobbed tentacles. (A, B, and c are after Milne-Edwards and Haime ; D is after Martin Duncan and Major-General Nelson.) by a large fasciculate " columella " or central rod. According to Mr Carter, the ancient and widely distributed forms re- ferred to Stromatopora and to allied genera are really closely related to Millepora, but this conclusion cannot be accepted without further evidence. We must also mention here the extraordinary forms known as the Stylasteridce, which have been shown by Mr Moseley to be true Hydroids, producing a calcareous corallum. But brief notice, however, can be given to the group, since there is at present only one known fossil example of it (Disticho- FOSSIL HYDROZOA. 173 pora antigua of the Tertiary of France). The family in- cludes several genera (Stylaster, Allopora, CryptoJielia, &c.), all of which secrete a branched calcareous skeleton, so closely resembling some undoubted corals (such as Oculina) that the group has always been regarded as referable to the Oculinidce. Taking Stylaster (fig. 66) as the type of the Fig. 66. A, Portion of the skeleton of Stylaster sanguineus, of the natural size ; B, Small portion of a branch of the same, enlarged, showing the calices and ampullae. Living in the Australian seas. (After Milne-Edwards and Haime.) group, we find the skeleton to be a branched calcareous structure, studded at intervals with cup - like depressions, each of which exhibits a central chamber, occupied axially by a styliform rod (" columella "), and surrounded by a series of secondary chambers, separated from one another by short partitions (" septa "), which appear to be formed by a folding of the wall. Though the general appearance thus produced especially as regards the existence of " calices " and " septa " - is distinctly that of the ordinary compound corals, yet Mr Moseley has shown that the animal forming this skeleton is truly a composite Hydroid. The colony consists of two sets of zooids, of which the larger and per- fect ones inhabit the central chambers of the calices, while the smaller chambers, marked off by the septa, are occupied by rudimentary and imperfect zooids, resembling tentacles in 174 CCELENTERATA. shape, and destitute of a mouth. The cavities of the zooids are placed in communication with one another by a complex system of canals, ramifying in the ccenosarcal skeleton ; and the true Hydrozoal character of these coral-like forms is shown by the fact that the reproductive organs are situated outside the bodies of the ordinary zooids, being in the form of fixed sporosacs developed within sac-like cavities ("ampullse") in the skeleton (fig. 66, B), which at certain periods communicate with the exterior by minute pores. LITERATURE. [The following are some of the more important works and memoirs which may be consulted by the student of the fossil Hydrozoa.~\ CORYNIDA. 1. "Fossil Hydractiniae." < Geological Magazine,' 1872. Allman. 2. " On the close Relationship of Hydractinia, Parkeria and Stromato- pora, with descriptions of new species of the former, both recent and fossil." ' Annals Nat. Hist.,' 1877. Carter. 3. "On Paleeocoryne." 'Phil. Trans.,' 1869. Martin Duncan and Jenkins. GRAPTOLITID.E. 4. " Graptolites de Boheme." Barrande. 1850. 5. " Ueber Graptolithen." Scharenberg. 1851. 6. "Die Graptolithen." * Versteinerungen der Grauwacken-forma- tion.' Geinitz. 1852. 7. " Graptolites of the Quebec Series." ' Descript. of Canadian Organic Remains.' Decade ii. Hall. 1865. 8. " British Graptolites." ' Siluria,' 4th Edition, Appendix. Car- ruthers. 1867. 9. " Monograph of the British Graptolitidse." Part i., General Intro- duction. Nicholson. 1872. 10. " Morphology and Affinities of Graptolites." ' Annals Nat. Hist.,' 1872. Allman. 11. " Notes on British Graptolites." ' Geol. Mag.,' 1873. Lapworth. HYDROCORALLIN.E. 12. "Contributions to the Natural History of the United States." Louis Agassiz. (The animal of Millepora is figured, vol. iii., pi. xv., and the genus is referred to the Hydrozoa.) 13. " Observations critiques sur la classification des Polypiers paleo- zoiques." Compt. Rend. t. Ixxx., 1875. Dollfus. FOSSIL HYDROZOA. 175 14. " Notes on Two Species of Millepora," &c. ' Phil. Trans./ 1876. Moseley. (This memoir also contains a note on the structure of a Stylaster.) 15. " Structure of a Species of Millepora occurring at Tahiti." ' Annals Nat. Hist.,' 1876. Moseley. 16. " Preliminary Note on the Structure of the Stylasteridse." ' Annals Nat. Hist.,' 1877. Moseley. 17. "On the Actinozoan Nature of Millepora alcicornis." ' Annals Nat. Hist./ 1876. Nelson and Martin Duncan. 18. " Recherches sur les Polypiers ; Cinquieme Memoire. Mono- graphic des Oculinides." 'Annales des Sci. Nat./ 1850. Milne-Edwards and Haime. (Descriptions and figures of Stylasterids.) 176 CHAPTEE X. FOSSIL ACTINOZOA. OF the living groups of the Actinozoa (see Table, p. 153), the Ctenophora and the Sea-anemones (Zoantharia malacodermata), from their absence of hard parts, are unknown in a fossil condition. The remaining groups viz., the Zoantharia sclerobasica, Zoantharia sclerodermata, Alcyonaria, and Rugosa secrete a hard skeleton, which is known by the general name of the " coral " or " corallum." All these groups, therefore, are known as fossils ; but they are of very un- equal importance. The Zoantharia sclerobasica are known by very few fossil representatives, and require to be little more than mentioned. The Alcyonaria, also, with the excep- tion of the remarkable group of the Heliolitidce, are of little geological importance. The Zoantharia sclerodermata and Rugosa, on the other hand, have left very numerous and interesting traces of their former existence the latter being almost altogether extinct, and both will require to be noticed at some length. Eegarded as a whole, the class of the Actinozoa appears, so far as we yet know, to have commenced its' existence in the Lower Silurian period, and to have attained its maximum of development at the pres- ent day. ORDER I. ZOANTHARIA. Tentacles simple, rounded ; soft parts in multiples of five or six. Sub-opder 1. Zoantharia malacodermata. Ex. Sea-anemone. Sub-order 2. Zoantharia sclerobasica. Ex. Antipathes. Sub-order 3. Zoantharia sclerodermata. Ex. Reef-building Corals. ZOANTHARIA. 177 A. ZOANTHARIA MALACODERMATA. Though, from their soft nature, unknown in a fossil condition, the Sea-anemones merit a brief description here, as they may be taken as the types of the order, and as the somewhat complicated struc- ture of the sclerodermio coral will thereby be rendered much more intelligible. Fig. (37. A, Actinia mesembryanthemum, one of the Sea-anemones (after Johnston) ; B, Section of the same, showing the mouth (a), the stomach (6), and the body-cavity (c). The body of a Sea-anemone (fig. 67) is a truncated cone, or a short cylinder, termed the " column," and is of a soft, leathery consistence. The two extremities of the column are termed respectively the " base " and the " disc," the former constituting the sucker, whereby the animal attaches itself at will, whilst the mouth is situated in the centre of the latter. In a few cases (Cerianthus and Peachia) the centre of the base is perforated, but the object of this arrangement is unknown. Between the mouth and the circumference of the disc is a flat space, without appendages of any kind, termed the " peristomial space." Round the circumference of the disc are placed numerous tentacles, usually retractile, arranged in alternating rows, and amounting to as many as 200 in number in the common Actinia. The tentacles are tubular prolongations of the ectoderm and endodeim, con- taining diverticula from the somatic chambers, and sometimes having apertures at their free extremities. The mouth leads directly into the stomach, which is a wide membranous tube, VOL. T. M 178 FOSSIL ACTINOZOA. opening by a large aperture into the general body-cavity below, and extending about half-way between the mouth and the base. The wide space between the stomach and column-wall is subdivided into a number of compartments by radiating vertical lamellse, termed the "primary mesen- teries," arising on the one hand from the inner surface of the body- wall, and attached on the other to the external surface of the stomach. As the stomach is considerably shorter than the column, it follows that the inner edges of the primary mesenteries below the stomach are free ; and these free edges, curving at first outwards and then downward and inwards, are ultimately attached to the centre of the base. Besides the primary mesenteries, there are other lamellse which also arise from the body-wall, but which do not reach so far as the outer surface of the stomach, and are called " secondary " and " tertiary " mesenteries, according to their breadth. The reproductive organs are in the form of reddish bands, which contain ova and spermatozoa, and are situated on the faces of the mesenteries. B. ZOANTHARIA ScLEROBASiCA. The members of this group are all composite organisms, consisting of numerous polypes, each of which has essentially the structure of a small Sea-anemone, united together by a common organised medium or "ccenosarc" (fig. 68). Each polype has, with Fig. 68. Part of a living stem of Antipathes anguina, of the natural size. (After Dana.) rare exceptions, six tentacles, and the entire organism is supported by an internal skeleton or " corallum." The coral is horny, and it is what is called " sclerobasic " that is to say, it forms an internal axis, over which the ccenosarc is spread, much as the bark encloses the wood of a tree. As the polypes are sunk in the coenosarc, and as this simply forms a rind for the coral, it follows that the polypes are outside the corallum. In other words, the polypes take no ZOAXTHARIA. 179 part in the secretion of the corallum ; but this is deposited solely by the coenosarc or common flesh by which the polypes are connected together. The corallum is sometimes simple and unbranched, but is more commonly branched and plant-like, and its surface, though occasionally smooth, is usually covered with minute spines, being thus readily distinguished from the grooved and striated sclerobasis of the Gorgonidae. The Zoantharia sclerobasica are not known as occurring in either the Palaeozoic or Mesozoic period. They appear for the first time in the Miocene Tertiary (Leiopathes vetusta). C. ZOANTHARIA SCLERODERMATA (HEXACORALLA). This group includes most of the so-called " corals," and is of very high geological importance. All the members of this group secrete a skeleton or " corallum," and this is necessarily the only part of the animal with which the palaeontologist has to deal ; so that it becomes necessary to enter into its structure at some length. The animal itself in the Zoantharia sclero- dermata, in its essential structure, resembles a Sea-anemone ; but it very often has the power of repeating itself by budding (gemmation) or cleavage (fission), so thatfrbm a simple it becomes a compound organism. It may therefore consist of a single " polype," or of many similar polypes united by a common flesh or " coenosarc." The corallum is what is called " sclerodermic," its essential peculiarity being that it is secreted by the polype or polypes. The sclerodermic coral, in fact, is an actual calcification of part of the tissues of the polype. When, therefore, we have a simple coral, produced by a simple member of this group (as in fig. 69), we have clearly to do with nothing but skeletal structures produced in the interior of the polype itself. When, on the other hand, we have a compound sclerodermic coral to deal with, we have usually more than this. We have, namely ; two parts or elements of the coral to consider : 1 . The parts of the coral secreted by each individual polype ; and, 2. The parts secreted by the coenosarc which unites all the polypes into an organic whole. A compound coral may be theoreti- cally regarded, therefore, as consisting of a_greater or less number of jmnple_jcorals, such as the preceding, united 180 FOSSIL ACTINOZOA. together by a greater or less quantity of calcareous matter secreted by the ccenosarc. The entire compound corallum consists, therefore, of a greater or less number of " corallites " bound together by a calcareous basis, which is secreted by the ccenosarc, and is called the " coenenchyma." In practice, however, this theoretical view of the subject is not always Fig. 69. Caryophyllia borealis. A simple sclerodermic coral, twice the natural size. Recent. (After Sir Wyville Thomson.) borne out. The compound corallum may, and often does, consist of a number of corallites produced by budding or cleavage from a primitive corallite, having their outer walls amalgamated, or more or less completely free, but not sunk in any general ccenenchyma. In other cases, the ccenenchyma, though not actually absent, is very much reduced in quantity. To comprehend the more intimate structure of a sclero- dermic coral, we may take a simple corallum, such as figured in fig. 69. Typically, such a coral is conical in shape, some- times discoid, sometimes cylindrical, but in all cases possess- ing an external " wall " or " theca," with an internal included space. The theca may be very imperfect, often porous or cribriform (" Perforate Corals "), or it may be strengthened by a secondary calcareous investment, termed the " epitheca." The " theca " encloses p, larger or smaller space which is ZOANTHARIA. 181 known as the " visceral chamber," is variously subdivided below, and superiorly presents itself as a shallower or deeper cup-shaped depression, termed the " calice." Within the calice is contained, in the living state, the stomach-sac of the polype ; and the visceral chamber below the calice is sub- divided into a number of vertical compartments the " in- terseptal loculi "this subdivision being effected by means of calcareous partitions or " septa," which spring from the inner wall of the theca, and are directed inwards towards the centre. The " septa " correspond with the " mesenteries " of the living animal, with which they agree in number and size. Some of them the so-called " primary septa " are much wider than the others, and may extend far enough inwards to meet in the centre of the visceral chamber (fig. 70, A). Others of the septa fall short of the centre by a Fig. 70. Diagram of the arrangement of the septa in the Zoantharia sclerodennata and Rngosa. A, Transverse section of a simple sclerodermic coral (Turbinolia), showing the theca, with its projecting ridges or "costse" outside, the visceral chamber and radiating septa inside, and the columella in the centre ; B, Transverse section of a simple Rugose coral (Cyatho- phyllum), showing the wall, costae, and septa. greater or less distance, and are known as the " secondary " and " tertiary " septa, according to their width. In the centre of the visceral chamber there may or may not be an axial calcareous rod, known as the "columella" (fig. 70, A). The structure of the columella varies in different cases, but it extends, typically, from the floor of the visceral chamber to the bottom of the calice, into which it projects for a greater or less distance, and the primary septa are often closely con- nected with it. 182 FOSSIL ACTINOZOA. The number of the septa (when present at all) varies, but there are never less than six of these structures, and however great the number may be, a " hemmeral " arrangement of the septa can be usually more or less clearly demonstrated in the corallum of the Zoantharia sclerodermata. Hence the name of Hexacoralla often applied to this group of corals. While the rule among the Zoantharia sclerodermata is that the septa are arranged in six systems (see fig. 70, A), and are, however numerous, some multiple of six, there are cases in which no such hexameral arrangement is demonstrable. Fig. fl.Caryophyllia (CyatMna) BowerbanU, from the Gault (Cretaceous). The left-hand figure represents a specimen imperfect above, and enlarged, showing the tuberculated costse. The right-hand figure is a magnified cross-section, showing the septa and pali. (After Milne- Edwards and Haime.) As connected with the septa, we may also notice here the structures which are known as "pali." These are " small processes which exist between certain septa and the columella (fig. 71). They generally arise from the base of the visceral cavity, or close to it, and pass upwards, united by one edge to the columella, and by the oth^r to the inner end or margin of the septa. When there is no columella, they are adherent ZOANTHARIA. 183 to the septa, present a free edge to the cavity in the axis of the corallum, and arise with the septa " (Duncan). They are only occasionally present. The septa, further, may, for all practical purposes, be re- garded as being continued in the Zoantharia sclerodermata through the wall, so as to become visible on the exterior. The outer surface of the theca thus comes to be covered with a series of vertical ridges or ribs, which are termed the "costse" (figs. 70 and 71). The costse vary much as to the distance by which they are separated from one another, and as to their breadth, their solidity, and their ornamentation with spines, tubercles, or teeth. Theoretically, the " interseptal loculi " are vacant spaces or vertical compartments, bounded laterally by the septa, and extending from the lower and lateral surfaces of the theca to the floor of the calice. In practice, however, the continuity of the interseptal loculi is liable to be more or less interfered with by the development of the structures known as " syn- apticulcc" " dissepiments," and " tabulce" The " synapticulae " are transverse calcareous bars which stretch across the inter- septal loculi, and form a kind of trellis- work, uniting the opposite faces of adjacent septa. They are characteristic of the Fungidce. The " dissepiments " are commonly present in a great many corals, and have the form of incomplete, ap- proximately horizontal plates, which stretch between adjacent septa, and break up the interseptal loculi into secondary compartments or cells. Lastly, the "tabulae" may be re- garded as highly developed dissepiments, and like them, are approximately horizontal, as a rule, at any rate. They differ from the dissepiments in the fact that they cut across the interseptal loculi at the same level. When fully developed (fig. 72), they are transverse plates, which extend completely across the visceral chamber, and divide it into a series of storeys placed one above the other, the only living portion of the coral being above the last-formed tabula. Tabulae are found in various of the Zoantharia sclerodermata, in some of the Alcyonaria, and in a great many of the Rugosa. The above is the essential structure of the typical form of a simple sclerodermic coral, and it is easy to see that it is 184 FOSSIL ACTLNOZOA. produced by the calcification, or conversion into carbonate of lime, of the lower portion of a polype similar in structure to an ordinary Sea-anemone. The " theca " of the coral corre- sponds to, and is secreted by, the " column-wall " or general wall of the body of the polype. The " septa," again, corre- spond with the " mesenteries," and, like them, are " primary," " secondary," or " tertiary," according as they reach the centre or fall short of it by a greater or less distance. We must remember, however, that it is only the inferior portion of the. body of the polype which is thus calcified. The tentacular disc and mouth are placed at some distance above the upper margin of the theca, and the digestive sac occupies the calice ; Fig. 72. A, Portion of the corallum of Favosiles favosa, of the natural size ; B, Portion of four corallites of Favosites Gothlandica, enlarged, showing the tabulae. whilst the whole of the space comprised within the theca is lined by the endoderm, and the whole of its outer surface is covered by the ectoderm. Having now considered the general structure of a simple sclerodermic corallum, as produced by a single polype, we must glance for a moment at that of a compound corallum of the same group. Such a corallum is the aggregate skeleton produced by a colony of polypes, each of which is essentially similar to a Sea-anemone in structure, and it varies in size and form according to the characters of the colony by which it is produced. Such a colony (fig. 73) consists of a number of polypes, which may spring directly from one another, or which may be united by a common flesh or " coenosarc," and corresponding differences are found in the resulting corallum. ZOANTHARIA. 185 In the former instance, as previously remarked, the compound corallum consists of an assemblage of separate " corallites," as the skeletons of the individual polypes are called, these beino- united with one another directly and in various ways. Fig. 73. Astrcea pallida, a compound sclerodermic coral, in its living condition. (After Dana.) Tn the latter instance the corallum consists of a number of " eorallites," and of a common calcareous basis or tissue, which unites the various corallites into a whole, is secreted by the coenosarc, and is known as the " ccenenchyma." The compound coralla are, of course, primitively simple, and they become composite either by budding or by cleavage of the original polype. The following are the principal methods in which this increase is effected ; and in considering this subject briefly, it will be as well to take into account not only the Zoantharia sclerodermata, but also the Rugosa, the modes of increase in the two groups being very similar : 1. Lateral or parietal gemmation. In this mode of increase the original polype throws out buds from some point on its sides between the base and the circle of tentacles, and these buds on becoming perfect corallites may repeat the process. This is one of the commonest modes of growth amongst the recent corals, and it gives rise chiefly to dendroid or tree- like corals. 2. Basal gemmation. In this method the original polype gives forth from its base a rudimentary ccenosarc, from w r hich new buds are thrown up, and which may have the form of root-like prolongations or of a con- tinuous horizontal expansion. The resulting coralla are usually massive or incrusting, and the youngest corallites are, of course, those placed on the periphery of the colony. 186 FOSSIL ACTINOZOA. 3. Calicular gemmation. This consists in the production of buds from the calicine disc of the parent corallite, which may or may not continue to grow thereafter, whilst the new corallites thus produced generally repeat the process. This mode of growth is exceedingly rare amongst the Zoantharia sclerodermata, and is never typically exhibited ; but it is a characteristic feature in many of the Rugose corals. In many of these (fig. 74), the original polype throws up from its calicine disc one or more new corallites, which kill the parent. These, in turn, produce others after a similar fashion, till the entire corallum assumes the form of an in- verted pyramidal mass resting upon the original budding polype. In other Ru- gose corals the calicine disc gives off but a single bud, which may repeat the process indefinitely till the corallum presents the appearance of a succession of inverted cones placed one above the other. 4. Fission. This process in the coralligenous Actinozoa is usually ef- fected by " oral cleavage," the divisional groove commencing at the oral disc, and . < 4. -Calicular gemmation as deep ening to a greater or less extent, seen in Lonsdaleia flonjonnis. Car- r . . boniferous. the proximal extremity always remain- ing undivided. According to Dana, in fission a new mouth is formed in the disc near the old mouth, and a new stomach is formed for the new mouth, round which the new ten- tacles are then developed. This, therefore, is not, strictly speaking, a subdivision into halves ; since one half carries off the old mouth and stomach. More rarely, fission "is effected by the separation of small portions from the attached base of the primitive organism, whose form and structure they subsequently, by gradual development, tend to as- sume." " The coral-structures which result from a repetition of the fissipar- ous process are of two principal kinds, according as they tend most to increase in a vertical or in a horizontal direction. In the first of these cases the corallum is ccespitose, or tufted, convex on its distal aspect, and resolvable into a succession of short diverging pairs of branches, each resulting from the division of a single corallite." In the second case the coral becomes lamellar. " Here the secondary corallites are united throughout their whole height, and disposed in a linear series, the entire mass presenting one continuous theca." Both these forms of corallum "are liable to become massive by the union of several rows or tufts of corallites throughout the whole or a portion of their height. An illus- tration of this is afforded by the large gijrate corallum of Meandrina, over the surface of whose spheroidal mass the calicine region of the combined corallites winds in so complex a manner as at once to suggest that re- ZOANTHARIA. 187 semblance to the convolutions of the hraia .which its popular name of Brain-stone Coral has been devised to indicate " (Greene). As to their habitat and distribution in space, all the living Zoantliaria sclerodermata are inhabitants of the sea, and there is no reason to suppose that any of the fossil forms were other than marine. At the present day, also, they attain their maximum development in warm seas ; and this was probably the case in past times too. In existing seas, further, as has been specially insisted on by Professor Martin Duncan, we find two great groups of the Sclerodermic Zoantliaria viz., those which inhabit tolerably deep water, and those which build the great masses of coral which are known as " coral- reefs." The deep-sea corals, though often attaining, as in- dividuals, a considerable size, and though often compound, never form massive aggregations or " reefs." This is due to the fact that, when composite, the separate corallites are not united together by a lax cellular coenenchyma, so that the colony cannot increase to an indefinitely large size. The deep-sea corals seem to have existed in all the great geological periods, from the Silurian upwards. The chief genera of this group at the present day are Caryopliyllia, Balanopliyllia, Flaldlum, Desmophyllum, and Sphenotrochus, amongst the simple forms ; and Lopholielia, Amphihelia, Dendropliyllia, and Astrangia, amongst the compound forms. The reef-building corals, when simple, are provided with special structures which enable the polypes to grow rapidly. The great majority of the reef-builders, however, are com- pound, and owe the large size to which they attain to the fact that the corallites are mostly united by a loose cellular ccenenchyma. The chief genera of reef-building Zoantharia in Mesozoic, Kainozoic, and Eecent times, belong to the families of the Astrceidce, Poritidce, and Madreporidce, though the Oculinidce and Fungidce also contribute to the formation of reefs. In the Palteozoic period, if true "reefs" can be said to have existed at all, they were built up essentially by Eugose corals. In Mesozoic times, however, true coral-reefs existed towards the close of the Trias in Western Europe, and largely 188 FOSSIL ACTINOZOA. in Oolitic times both in Western Europe and in England. In the earlier portion of the Tertiary period, again, vast coral- reefs were formed in Central and Southern Europe, in Egypt, Syria, and Arabia, and in parts of India. As to the distribution in time of the Zoantharia sderoder- mata, it is difficult to speak with precision, as much doubt obtains as to the true systematic position of many ancient forms often referred to this group. It may be certainly affirmed, however, that the group attained no strikingly pre- dominant position during the whole of the Palaeozoic epoch ; that it underwent a great development in the Secondary and Tertiary periods ; and that it has, perhaps, reached its maximum at the present day. The Zoantharia sderodermata were divided by Milne- Edwards and Haime into the four sections of the Aporosa, Perforata, Tabulata, and Tubulosa, of which the two first are large and natural divisions, while the two latter are of doubtful affinities and uncertain value. We shall, however, briefly consider the characters, geological distribution, and leading types of each of these sections. I. APOROSA. The Aporose Zoantharia possess a corallum composed of more or less compact calcareous tissue," the " theca " or wall surrounding the visceral chamber being complete, and rarely perforated ~by apertures or pores. The septa are well devel- oped, and usually constitute complete lamellae ; and though dissepiments or synaptieulae are present, tabulae very rarely exist. Taken as a whole, the Aporosa are an essentially Sec- ondary and Tertiary group, being represented during both these periods by an immense variety of types. In the Palaeozoic period, there is still some doubt as to the precise position and structure of some of the corals which have at one time or another been regarded as ancient forms of the Aporosa. The Silurian genus Palceocyclus, usually referred to the Fungidce, appears to belong rather to the Eugosa ; but it is possible that the genus Columnaria (Favistella), from the APOROSA. 189 same formation, should be looked upon as a tabulate form of the Astrceidce. By Prof. Martin Duncan, the Battcrsbyia of the Devonian, and the Heterophyllia of the Carboniferous, are considered old types of the Astrceidce. Lastly, some of the forms placed in the badly-characterised genus Petraia, of the Silurian and Devonian, may very probably turn out to be Turbinolidce, and this may possibly be the place of the Silurian Duncanella. The Aporosa are divided into the following families : 1. Turbinolidce. In this family the corallum may be simple or compound, but in the latter case it is without a cosnenchyma. The inter septal loculi are open from top to bottom, and are not crossed by dissepi- ments or synapticulse ; and the septa are mostly granulated on their sides. Leaving the doubtful ancient forms (Petraia and Duncanella) out of sight, the family makes its first certain appearance in the Lias (Thecocyathus). In the Cretaceous numer- ous forms are known, and in the Eocene Tertiary a still greater development of this type takes place, after which the family begins to decline in numbers to the pres- ent day. In Turlnnolia itself (fig. 75) the coral- lum is simple and conical, with a styliform columella, but without pali. The costae are very prominent, and the spaces be- tween them are marked with rows of small dimples, which look like perfora- .. . TIT i -i 11 i tlOnS 111 the Wall, but Which really do sulmta. The upper figure not penetrate to the visceral chamber. Turbinolia The genus is characteristic of the Eocene The lower fi ? ure 8hows , ~ the calice, with the col- penod. Flabellum, ranging from the LO- umella and primary and cene Tertiary to the present day, is nearly ^ dary septa " allied to Turbinolia, but the corallum is compressed, so as to produce an elliptic form of calice, and the wall is covered with a thin epitheca. Caryophyllia, 190 FOSSIL ACTINOZOA. ranging from the Cretaceous to the present day, is another close ally of Turbinolia, from which it differs principally in the possession of a crown of "pali" (fig. 71); while the widely distributed Trochocyathus of the Jurassic, Cretaceous, and Tertiary formations, possesses more than one circle of these structures. 2. Pseudoturbinolidce. In this family we have only the extinct genus Dasmia, of the Cretaceous and Tertiary, in which the corallum is in most respects similar to that of the Turlinolidce proper, but each septum is composed of three laminae united externally by a single costa. 3. Oculinidce. The corallum in this family is always Fig. 76. Syrihelia Sharpeana. Cretaceous. compound (fig. 76), with an abundant and compact ccenen- chyma, its surface smooth or striated, but never echinulate. The wall of the corallites is imperforate, not distinct from the coenenchyma, the lower portion of the visceral chamber becoming filled up with advancing age. A few dissepiments are present, but no synapticulse. The Oculinidce appear for the first time in the Oolitic rocks (Huhelia, EnalloJielia), and are also represented in the Cretaceous (Synhelia, fig. 76, and Diblasus). In the Eocene Tertiary we meet with Oculina itself, with its arborescent corallum and nearly smooth ccenenchyma. The well-known living genera Lophohelia' and Amphihelia are found in the APOROSA. 191 late Tertiaries, and Diplohelia is Eocene 'and Miocene. From the researches of Verrill, it would appear that Pocillopora (Miocene to Eecent), formerly referred to the Tabulata, should be placed here, in which case we have a member of this family exhibiting "tabulae" in a well -marked form, these structures being occasionally present in Lophohelia also. Probably the genus Seriatopora (which has been said to occur even in the Palaeozoic rocks) should likewise be referred to this family. On the other hand, the limits of the group have been contracted in another direction by the removal of Stylaster and allied genera to the Hydrozoa. 4. Astrceidce. In this, the most important of all the families of the Zoantharia sclerodermata, the corallum may be simple or compound, usually increasing in the composite Fig. 77.- Columnar ia (?) Halli, showing the corallites partitioned off into storeys by tabulae. Silurian. forms (fig. 73) by fission. There is no, or little, coenenchyma, but an abundance of dissepiments, without synapticulae or tabulae. Little is known of the distribution of Astrceidce in the Palaeozoic period, but, as before said, Dr Martin Duncan, one of the highest of authorities on this subject, regards the Devonian Battersbyia and the Carboniferous Heterophyllia as ancestral and aberrant types of the family (Palastrceidce). If it were not, also, for the presence of tabulae, we should place the Silurian genus Columnaria in this family, and as it is now admitted that tabulae have little or no systematic sig- nificance, it is difficult to see how this old form can be 192 FOSSIL ACTINOZOA. excluded from the Astrceidce. In the Columnarice proper ( - Favistella) the septa are very well developed, but in other forms often referred here (fig. 77) the septa are rudimentary. Leaving the Palaeozoic period, we find a great develop- ment of Astrceidoe to take place towards the close of the Trias where the family is represented by numerous and varied types ; a still further expansion takes place in the Oolites ; very numerous forms are met with in the Cretaceous, and though there is some decrease in the Tertiaries, this great family still holds its ground as the most important group of the " reef-building " corals. Of the many genera of this family, only two or three of the most important can be so much as alluded to here. Of the simple forms of the family, we may take Montlivaltia (fig. 78), and Trochos- milia as typical examples the former genus ranging, under many specific forms, from the Triassic to the Tertiary inclu- sive ; while the latter, also with many species, begins in the Jurassic, and con- tinues to the later Tertiaries. These simple types may be regarded as transi- tional between the Astrceidce and Tur- *olidce. Such forms as Thecosmilia (fig. covering the "79^ again, may be compared to a colony " lower part of the coral. ,,- , 7 . 7 , ,1 -IT, Great Oolite. ot MonUivaUice, the separate corallites being bound together by a strong "epi- theca," and united into a tufted corallum. The species of the genus are numerous, and are found in the Juras- sic, Cretaceous, and Tertiary periods. In a third group of Astrceidce we have very numerous and important forms, which agree with the last mentioned in being compound, but in which the corallum consists of numerous closely-approxi- mated corallites, produced by fission, and giving rise, as a rule, to massive " astrseiform " colonies. Of these " star- corals," Astrcea itself may be taken as the type, though not known to have existed earlier than the Tertiary. In the Secondary period, however, we have a vast development of APOROSA. 193 forms more or less closely related to the living Astrcea, such as Prionastrcea, Isastrcea (fig. 80), Sepfastrcea, Convexastrcea, Tkamnastrcea, Heliastrcea, &c. Lastly, not to mention others, Fig. 79. Thecosmilia annularis. Coral -rag, England. we have a group of forms very similar to the preceding, but having the calices of the separate corallites more or less com- pletely confluent with one another. As examples of this V\. 80. Inunlrffia ullunya; portion of u small polished slab, of the natural size, and a few calices enlarged. Jurassic (Portland Oolite). group, we may take Meandrina (the " Brain-corals "), Lati- meandra, and Diploria. 5. Fungidce. In this group, the corallum is simple or compound, usually discoidal or laminar, the calices shallow VOL. I. N 194 FOSSIL ACTINOZOA. and open in the simple forms, confluent in the compound forms, with complete imperforate septa, the edges of which are dentate ; while the interseptal loculi are crossed by num- erous trellis-like bars (" synapticulae "). The wall is generally basal in the discoid forms always so and is generally perforated by apertures. There are no dissepiments nor tabulre. Fig. 81. Cyclolites elliptica, a simple type of the Fungida',, viewed from above, from below, and from the side. Cretaceous. If we except the Silurian Palceocyclus (which appears to be truly a Rugose Coral), the Fwngidce are not known to have existed prior to the Jurassic, in which they are represented by numerous forms (Comoseris, Protoseris, Anabacia, &c.) Numerous forms are known in the Cretaceous, and there is also a considerable number of Tertiary species. As an example of the family we may take the genus Cyclolites (fig. 81), which ranges from the Cretaceous to the Miocene Ter- tiary inclusive. In this genus the corallum is simple and discoid, with a concentrically - striated basal epitheca and numerous delicate septa. Micrabacia, of the Cretaceous, is like Cyclolites, but has no epitheca, and has its basal wall perforated ; while in the Jurassic Anabacia, also very similar to the preceding, the basal wall is imperfect, so that the under side of the disc is covered by the projecting septa. 6. Pseudofungidce. This, the last family of the Aporosa, merely requires mention, as affording a connecting link between the Fungidoe and Astrceidce, the corallum agreeing with the former in having a perforated basal plate, but PERFORATA. 195 resembling the latter in having no synapticulai, and in pos- sessing dissepiments. The only genus of this family is Merulina, and it is not known to possess any fossil repre- sentatives. II. PERFORATA. In the Perforate section of the Zoantharia sclerodermata, the calcareous tissue of the corallum is more or less porous, often spongy or reticulate, the " wall " of corallites being always perforated by more or fewer apertures. The septa may be well developed, but they are usually more or less porous, and are sometimes represented by mere calcareous trabeculse. There may be imperfect dissepiments, and sometimes there are well- developed tabulae, but in general the visceral chamber is open from top to bottom, the interseptal loculi being continuous. Taken as a whole, the Perforate Corals must be regarded as an essentially Tertiary and Recent group. The only Palaeozoic Corals which can at present be referred to the Per- forata, with anything like certainty, are the Protarcea of the Lower Silurian, and the Calostylis of the upper division of the same formation. The Lower Silurian genus Columnopora may possibly be one of the Poritidce, and there is con- siderable probability that the true place of the great and important family of Palseozoic Corals termed the Favositidce is truly in this section, but we shall provisionally consider these among the Tabulata. In deposits later than the Silurian, the only forms which have been referred here namely, Plcurodictyum and Palceacis are certainly wrongly placed, the former being founded upon casts of a member of the Favositidce, while the latter is probably a sponge, and is apparently not a coral. In the Permian rocks, the Trias, and the Lias, no Perforate Corals are known ; and in the Oolitic series we have only the aberrant genus Microsolena (including Dendrarcea), an ancient type of the Poritidce. In the Cretaceous series, however, we have examples of all the existing families of this section, and in the Tertiary period we find a great development of Perforate Corals, the group apparently reaching its maximum at the present day. 196 FOSSIL ACTINOZOA. The Perforate Corals are divided into the following three families if we omit the Favositidce, the true place of which is still uncertain : 1. Eupsammidce. In this family the corallum may be simple or compound, the wall being always perforated and granular, while the septa, though comparatively well devel- oped and lamellar, are generally also perforated. There is a spongy columella, and the interseptal loculi are open, or crossed by but few dissepiments. Fig 82. Endopachys Madurii, viewed in profile and from above. Eocene Tertiary. The most ancient type of the Eupsammidce is the Upper Silurian Calostylis, but with this exception the earliest known representatives of this family occur in the Cre- taceous (StepJianophyllia\ and there is a considerable ex- pansion of the group in the Eocene Tertiary. In Eupsam- mia itself, the corallum is simple, free, and turbinate in shape; and Endopachys (fig. 82) is essentially the same, except that it is much compressed, and its keeled base is continued into two wing-like expansions. Balanophyllia, ranging from the Eocene to the present day, is also simple, but the corallum is fixed ; while the Cretaceous and Tertiary StephanopJiyllia is free, simple, and discoid, with an open circular calyx. Dendrophyllia, again, a well-known recent type, is composite, the corallum increasing by lateral gem- mation, so as to assume a dendroid or shrub-like form. It begins in the Eocene Tertiary. 2. Madreporidce. The members of this family are dis- tinguished by possessing a composite corallum, increasing by gemmation, the various corallites being united by an abundant and spongy ccenenchyma. The walls of the coral- lites are not distinct from the ccenenchyma, and are porous, PERFORATA. 19*7 and the septa are often well developed. There are no syn- apticulse, and usually no dissepiments, but there may be tabula?. The family makes its first undoubted appearance in the Cretaceous (Actinacis), and is largely represented in the Tertiaries, and by living forms in the " coral-reef region " of the present era. The genus Madrepora itself, with its lobate, ramose, or fasciculate corallum, and its loose and delicately echinulate ccenenchyma, appears for the first time in the Eocene Ter- tiary, and survives to the present day ; while the range of the allied genus Astrceopora is essentially similar. 3. Porit'idce. In this family the corallum is entirely made up of reticulated calcareous tissue (" sclerenchyma "). Fig. 83. Alveopora spongiosa, one of the recent Poritidce (after Dana). A, Some of the corallites cut vertically and enlarged, showing the tabulae and the perforated walls ; B, View of the calices from above, enlarged. The septa are not lamellar, but are composed of styliform processes, which constitute by their junction a sort of trellis- work, and the walls are similarly constructed and are not distinct from the ccenenchyma, when this is present. There are a few dissepiments, but generally no tabulae. The oldest known types of the normal Poritidce appear in the Silurian, where the family is represented by the curious Protarcea and the nearly allied Stylaroea, both of which are believed to be closely related to the Tertiary genus Litharcea. In the Oolitic rocks we meet only with the singular genus Microsolena (fig. 84), but in the Cretaceous we find Porites itself. In the Tertiary rocks, again, the family is well re- presented, principally by the still existing Porites, Alveo- 198 FOSSIL ACTINOZOA. pom (fig. 83), and Rhodarcea. The genus Alveopora is one of special interest, as its corallites are provided with well- developed tabulae (fig. 83, A). The closely- allied Favositipora of Mr Saville Kent, found both in the Devonian and in existing seas, not only possesses ta- bulae, but is in other respects extremely sim- ilar to some of the Fa- vositidce. It seems, in fact, impossible to doubt that the place of the large and principally Palaeozoic family just mentioned is in the vicinity of the Poritidce, though, in deference to long re- ceived and still current systems, we shall here retain it in the provisional group of the " Tabulate Corals." Fig. 84. Fragment of Microsolena (Dendrarcea) ramosa, and three of the calices of the same, enlarged. Jurassic. III. TABULATA. The group of the " Tabulate Corals," as founded by Milne- Edwards and Haime, included a large number of corals, in many respects very unlike each other, but characterised by the rudimentary condition or absence of the septa, conjoined with the presence of well - developed tabulce dividing the visceral chamber into so many distinct stories. It is now known, however, that the presence of tabulae cannot be re- garded as a point of any great classificatory value ; and the researches of naturalists, and especially of Verrill and Moseley, into the structure of living forms have shown that the various recent " Tabulate Corals " are of the most diverse nature. Thus it has been shown that Pocillopora (and prob- ably Seriatopora also) is a true Aporose Zoantharian. On the other hand, the living Heliopora is not a Zoantharian at all, but a genuine Alcyonarian ; and this discovery removes TABULATA. 199 to the Alcyonaria the great group of extinct " Tabulate Corals " of which Heliolites is the type. Lastly, Millepora, as originally affirmed by Agassiz, has been shown to be like- wise not a Zoantharian, but to be referable to the Hydrozoa. In spite of these great deductions, there still remain some extinct groups of corals which may, in the meanwhile, be retained to form the section Tabulata, though their true affinities and systematic position are matters of great doubt. 1. Favositidce. The first of these groups comprises the well-known " honeycomb " corals, and is almost exclusively Palaeozoic in its range. In all the members of this family the corallum is compound, the septa are rudimentary or absent, the tabulae are extremely well developed, and the walls of the corallites are perforated more or less freely with apertures or "mural pores" (fig. 72). In their per- forated walls and general structure the Favositidce make such a near approach to such living genera as Alve-opora and Fig. 85. Portion of a mass of Favosites ( iothlandica, of the natural size. Upper Silurian and Devonian of Europe and America. (Original.) Fig. 86. Fragment of Parasites (Emmon- sia) Tiemispherica, of the natural size. Up- per Silurian and Devonian of America. (After Billings.) Favositipora, that it seems certain that they will ultimately be removed from the "Tabulata'' and will be placed in the Zoantharia Perforata, in or near the family of the Pori- tidce. The type-genus of this family is Favosites itself, with many species in the Silurian, Devonian, and Carboniferous rocks. The corallum in this genus is massive or branched, composed of more or less prismatic, closely approximated 200 FOSSIL ACTINOZOA. corallites, which are often enveloped basally by a common epitheca, and have their walls pierced by one or more rows of regular apertures (" mural pores "). The septa are absent or spiniform, and the tabulae, though usually complete, are sometimes imperfect (Emmonsia, fig. 86). The genus Michc- linia (fig. 87) possesses a corallum very like that of the massive forms of Fawsites ; but the epitheca is often fur- nished with root -like prolongations, the tabulae are arched and somewhat vesicular, and the mural pores are numerous and usually irregularly distributed. The genus is essentially Devonian and Carboniferous. Fig. 87. Michelinia convexa (D'Orbigny). Devonian. In the genus Alveolites, again, palaeontologists usually in- clude a number of branching or massive corals, which agree with Favbsites in most respects, but which have short oblique corallites, with sub-triangular or crescentic calices (fig. 88). Nearly allied to Alveolites are the genera Cce-nites and Pachy- pora, of the Silurian and Devonian. Of the remaining genera of the Favositidce, Striatopora (fig. 89), of the Silu- rian and Devonian, is remarkable for the form of its calices ; and Koninckia is specially noticeable as being found in strata as young as the Cretaceous. 2. Chcetetidce. In this family we have a great number of Palaeozoic corals, in which there is a compound corallum TABULATA. 201 (fig. 90), composed of closely approximated corallites, des- titute of septa, provided with well-developed tabulae, and differing from the Favositidce chiefly in the fact that the walls of the corallites are imperf orate. Though ranging from Fig. 88. a, Fragment of Alveolites ramulosa, of the natural size ; 1>, Portion of the same enlarged, showing the calices ; c, Fragment of Alveolites Billimjsi, of the natural size. Devonian. (Original.) . the Lower Silurian to the Permian, inclusive, we have no Mesozoic or Tertiary representatives of this family, so far as is certainly known. Though presenting a striking general resemblance to the Farositidcc, it is very doubtful if any close relationship exists between the Chcetetidce and the former. The family, indeed, may possibly be really Alcyonarian, though at present the evidence would rather point to its ultimate removal to the Polyzoa. At any rate, it should be remem- bered that we have Mesozoic, Tertiary, and Eecent Polyzoa (such as Heteropora), which can hardly be distinguished from the Chcetetidce except by their not possessing tabulae. The chief genus of this family is Chcetetes itself (pro- visionally including under this name the forms known by the name of Monticulipora) ; and it is widely represented Fig. 89. Fragment of Striatopora flexu- osa of the natural size, and two calices enlarged. Upper Silurian. (After Hall.) 202 FOSSIL ACTINOZOA. by numerous and varied forms in the Silurian, Devonian, Carboniferous, and Permian rocks. The corallum is some- times massive, sometimes branched, sometimes laminar, and sometimes encrusting ; the corallites are prismatic, gen- erally of small size, always with imperforate walls ; and the tabulae are numerous and well developed. In some species Fig. 90. Clicetetes petropolitanus. A, A specimen viewed sideways, of the natural size ; B, A horizontal section of the same, highly enlarged ; c, A vertical section of the same, greatly enlarged, showing the tabulae. Lower Silurian. (Original.) of Clicetetes as in other members of this family some of the corallites are of larger size than the others ; this prob- ably indicating that the colony was composed, in its living condition, of two distinct and different sets of zooids. The genera Prasopora, Dania, Dekayia, and Constellaria, are nearly allied to Chcetetes, and are all Silurian. Beaumontia, closely resembling Favosites in form, is Carboniferous. It is probable, also, that we should include in this family the closely allied or identical genera, Fistulipora and Callopora, both of which are well represented in the Silurian and Devonian, but which present many striking points of like- ness to the Polyzoa. 3. Thecidce. This family includes only the single genus Thecia, confined to the Silurian period. The corallum is compound, septa are present, and tabula? are well developed. The precise affinities of this genus are still obscure, but there is a considerable probability that it should really be re- garded as an Alcyonarian, and placed in the neighbourhood of Heliolites. 4. Halysitidce. In this family we have the most typical of the " Tabulate Corals," or, at any rate, those which appear most likely to hold their ground as a separate division of the Zoantharia. The corallum is always compound, rudimentary TABULATA. 203 septa (typically twelve in number), are mostly present, there are well-developed tabulae, and the walls are imperforate. In Halysites, the " Chain-coral," which may be taken as the type of this family, the corallum (fig. 91), consists of long tubular corallites, united to one another in such a way as to form vertical plates or expansions, which, in turn, are so disposed as generally to form by reticulation a loosely netted mass. The tabulae are horizontal. The " Chain- corals " are characteristically Upper Silurian forms, but they occur also in the Lower Silurian. d Fig. 91. a, Halysites catenularia, small variety, of the natural size ; b, Fragment of a large variety of the same, of the natural size ; c, Fragment of limestone with the tubes of Halysites agglomerate, of the natural size ; rf, Vertical section of two tubes of the same, showing the tabulae, enlarged. Niagara Limestone (Upper Silurian), Canada. (Original.) The genus Syringopora (figs. 92-95), is in many respects closely allied to Halysites, though very different in external aspect. The corallum is fasciculate, the corallites being cylindrical, lengthy, and united by hollow, tubular, hori- zontal connecting-processes ; so that though the wall is im- perforate, the visceral chambers of contiguous corallites are placed in communication. Septa, though very rudimentary, are not wholly absent, and the tabulae have the form of funnel-shaped plates invaginated into one another. Young forms, and the basal portions of old colonies, closely resemble 204 FOSSIL ACTINOZOA. the Tubulose genus Aulopora, from which they can only be separated by the presence of infundibuliform tabulae. The Fig. 92. Syringopora retiformis. A Silurian Tabulate Coral. Fig. 93.Syringo}:ora verticillaUt. Silurian. Fig. 94. Syringopora Dalmani. Silurian. Fig. 95. Syringopora compacta. Silurian. species of the genus are widely distributed in the Silurian, Devonian, and Carboniferous formations. The remaining genera of the Halysitidce have little general interest ; but it may be men- tioned that one (Fletcheria) is said to range as high as the Trias. With this exception, the family seems to die out in the Carboniferous. The curious Silurian genus, Tetradium, widely distributed in North America, may also be noted here, as affording a link between the Halysitidce and the Chcetetidce. Fig. 96. Aulopora serpens. Devonian. IV. TUBULOSA. This is a small group of corals, including the genera Aulo- pora and Cladochonus (Pyrgia}, to which, perhaps, Stomato- pora should be added. The corallum may be simple or com- pound (fig. 96), the corallites being pyriform, or trumpet- TUBULOSA. 205 shaped, without tabulae, and having the septa indicated by mere striae on the wall (fig. 97, B). The family is entirely Palaeozoic, and its systematic position is wholly doubtful. Save for the alleged absence of tabulae, its nearest ally ap- pears to be Syringopora. In Aulopora, a genus which ranges from the Silurian to the Carboniferous, the corallum (fig. 97, A) is compound, and grows parasitically upon foreign bodies. The corallites are Fig. 97. A, Portion of Aulopora tubceformis, of the natural size ; and B, Portion of the same, enlarged (after Goldfuss). Devonian, c, Cladochonus (Pyrgia) Michelini, of the natural size, and enlarged (after Milne-Edwards and Haime). Carboniferous. tubular or pyriform, produced by lateral gemmation, and furnished with a strong imperforate wall. In the Carbon- iferous genus Cladochonus (Pyrgia), on the other hand, the corallum is typically simple, and resembles a free corallite of Aulopora. 206 CHAPTER XL RUGOSA AND ALCYONARIA. ORDER II. RUGOSA. THE order of the Rugosa includes an enormous number of fossil corals, the vast majority of which are confined to the Palaeozoic period. Throughout the Lower and Upper Silu- rian, the Devonian, the Carboniferous, and the Permian, the Rugosa, are the principal representatives of the Ocelenterata ; but the order is not known to be represented at all during the Triassic or Jurassic periods rich as the latter is in the remains of corals and in the Cretaceous we find only the singular little Holocystis of the Lower Greensand. In the great series of the Tertiary deposits, again, there has been discovered but one Rugose genus viz., the Conosmilia of the later Tertiaries of Australia. Lastly, at the present day we find only two living genera (HaplopJiyllia and Guynia) which have any title to be regarded as Rugose Corals. While, therefore, we may well admit that our knowledge of the history of the Rugose Corals since the close of the Permian period is extremely imperfect and fragmentary, still it re- mains certain that the group is an essentially Palaeozoic one, and that it underwent a very marked diminution before the commencement of Mesozoic time. As regards their general characters, the Rugosa agree with the Zoantharia sclerodermata in possessing a well-developed sclerodermic corallum, with a true tkeca, and generally pre- senting well-developed septa, though these are usually com- RUGOSA. 207 bined with tabulce as well. The corallum may be simple or compound, but in the latter case a true ccenenchyma is not present. Seeing that there is this striking general likeness between the corallum of the Rugosa and that of the Zoantharia sclero- dermata, and seeing, further, that the only living forms which have any claim to be regarded as Kugose Corals are unques- tionable and undoubted Actinozoa, it would seem that there ought to be little difficulty in deciding as to the systematic position of the Rugosa, unless it were in separating them satisfactorily from the Zoantharia, Of late years, however, an opinion first started by the late Prof. Agassiz has gained considerable acceptance, according to which the Rugosa are to be considered as really belonging to the Hydrozoa. So far as any actual evidence in support of this view goes, it can only be said that we really do know now of living Hydrozoa which do secrete a calcareous skele- ton (Millepora and the Stylasteridce). The skeleton of these forms, however, does not present any special resemblance to that of the Rugosa, and its characters, indeed, are such that its makers till their soft parts were investigated were always referred to the Zoantharia. It is clear, therefore, that the existence of coralligenous Hydrozoa cannot be used as an argument for removing the Rugosa from the Actinozoa. On the other hand, the resemblances between the corallum of the Rugosa and that of the Zoantharia sclerodermata are so numerous and so weighty, that it is difficult to imagine that the coralla in the two cases were secreted by different methods, or bore dissimilar relations to the soft parts of the animals producing them. Thus, in both groups alike the simple form of corallum (fig. 98) consists of an outer wall or " theca," enclosing a central space or " visceral chamber," which is ordinarily divided into a series of compartments by vertical partitions or " septa ; " in both alike the " visceral chamber " may be partitioned off into storeys by horizontal plates or " tabulse ; " in both alike the interseptal loculi are liable to be more or less subdivided by " dissepiments ; " and in both alike the axial rod, known as the " columella," ' may be developed. In both groups alike, moreover, the 208 RUGOSA AND ALCYONARIA. corallum is often composite, and may be regarded as a variously formed aggregate of " corallites," each of these subordinate elements of the colony being essentially similar in structure to the typical simple corallum. Fig. 98. Morphology of the Rugosa. A, Fragment of Zaphrentis gigantea, showing the septa (s), with the sparse dissepiments crossing the interseptal loculi, the epitheca (e), and the thin proper wall (w) ; B, Transverse section of Zaphrentis Guerangeri,-show'mg the septa and dissepiments, the central area occupied solely by the tabulae, and the "fossula" (/) ; c, Longitudinal section of the last, showing the arrangement of the tabulse. (A is after Edwards and Haime ; B and c are after James Thomson.) On the other hand, there are various points in which the corallum of the Rugosa differs from that of the Zoantharia sclerodermata, and some of the more important of these differences may be briefly alluded to here. In the first place, the "septa" appear to be primitively developed in four systems, so that the corallum is fundamentally con- structed upon a tetrameral, instead of an hexameral type. In some cases, as in Stcmria (fig. 100, A), this quadripartite disposition of the septa is very conspicuous, since there are four pre-eminently large septa, which form a cross in the centre of the calice. In the genus Anisophyllum (fig. 100, B and c) there are three of these pre-eminently developed septa. In the second place, the septa usually present them- selves in the adult as of two sizes only, a larger and a 'smaller; and their arrangement is very generally rendered irregular by the presence of a singular vacant space, which RUGOSA. 209 is known as the " fossula " or " f ossette " . (fig. 98, B, and fig. 99). This space appears to take the place of one of the four principal septa, and usually presents itself as a more or Fig. dd.Zaphrentis cornicula, the walls of the ealice broken away, and showing the " fos- sula," of the natural size. Devonian, America. (Original.) Fig. 100. A, A few calices of Stau- ria astrceiformis, enlarged Silurian ; B, Anisophyllum Agassizi, slightly enlarged ; c, Calice of same, viewed from above DevonUfi. (After Milne- Edwards and Haime.) less conspicuous depression or groove in the ealice. Some- times there may be two small lateral fossulse, and in other cases (Omphyma) there are four shallow fossulas arranged in a crucial manner. In the third place, the corallum of the lluyosa generally exhibits tabulse in conjunction with well- developed septa ; whereas in the Zoantharia sclerodermata, if the tabulse are conspicuously developed, the septa are rudimentary or wanting, and vice versa. The tabulae of the Ruyosa may be " complete," passing completely across the visceral chamber from side to side (fig. 98, c), or they may be confined to a larger or smaller central area. Lastly, the VOL. I. O 210 RUGOSA AND ALCYONARIA. corallites of the compound corallum of the Rugosa are never connected by a true ccenenchyma. Sometimes the corallites are placed in close contact, so that the corallum becomes " massive," and then they are usually united by a fusion of their walls. Sometimes the walls are wanting, and the corallites are united to one another by the extension and confluence of their septa, as is seen in the genus Phillips- astrcea (fig. 101), or the union may take place by the Fig. IQl.~-PhittipM8trcea Verneuilli. From the Devonian (Corniferous Limestone) of N. America. development of lateral processes, very much as we have seen in Syringopora. The production of compound coralla is principally effected by lateral and calicular gemmation, the latter process (see p. 186) being especially characteristic of the Rugose Corals. The divisions of the Eugose Corals which were laid down by Milne-Edwards and Haime, and which have subsequently been generally adopted, are as follows : 1. Stauridce. In this family the corallum may be simple or compound, the septa are well developed, conspicuously arranged in four systems, and both dissepiments and tabulae are present. In Stauria (fig. 100, A), which is the type of the family, there is a compound astreeiform corallum, four of the prin- cipal septa forming a cross in each calice. The increase of the corallum is effected by calicular gemmation, and there is no columella. The genus is wholly Silurian in its range. The genus Holocystis (fig. 102) is closely allied to Stauria, but the corallites are united by their costse, and a styliform columella is present. It is remarkable as being the sole RUGOSA. 211 B representative of the Rugosa at present known from deposits of Secondary age, occurring, as it does, in the Lower Green- sand (Cretaceous). The re- maining members of the Stauridce possess a simple corallum. In Metriophyl- lum, of the Devonian, the septa are arranged in four groups, separated by as many fossulse ; and in the Permian Polyccelia the sep- ta are divided by four prin- cipal ones into as many sys- tems. The Tertiary genus Conosmilia may perhaps be associated with the above, but its systematic position is not free from doubt. 2. Cyathaxonidce. In this family the corallum is simple, the septe are well developed^ and the inter- septal loculi are open, and are not partitioned off by dissepiments or tabulae. In many respects this family is very nearly allied to the family of the Turbinolidce, among the Zoantharia sclerodermata, but the septa have a tetrameral arrangement. Cyathaxonia, the type -genus, has a styliform columella (fig. 103), and ranges from the Silurian to the Carboniferous. 1 The living genera, Haplophyllia and Gkiynia, are referred here, but no Secondary or Tertiary members of the family are known. 3. CyatJwpliyllidce. In this, by far the largest and most important family of the Rugose Corals, the corallum may be simple or compound, the septa are not arranged in a con- 1 Recent researches have shown that some of the forms usually referred to Cyathaxonia (such as C. Dalmani) really possess tabulae, and are in other respects entitled to be regarded as forming a separate genus, for which the name of Lindstromia has been proposed. Fig. 102. A, Small mass of Holocystis elegans, of the natural size ; B, A few caliees of the same, enlarged. Cretaceous. (After Milne- Edwards and Haime.) 212 RUGOSA AND ALCYONARIA. spicuously quadripartite manner, except in a few cases ; tabula? are always present, and the interseptal loculi are more or less broken up by the development of dissepiments. The family is wholly Palae- ozoic in its distribution, and it is divided into the two great tribes of the Zaphren- tince and CyathopJiyllince. In the Zaphrcntince, the corallum is simple and free, conical, discoidal, or cylin- drical in shape, with complete tabulae, and usually few dissepiments. The septa are Fi S .iw.-cyatka X onia rendered more or less irregular by the Daimam. A portion of presence of a septal fossula. In Zapli- wall of the theca is ' ' i n i i ni broken, in order to show TentlS itself, which IS the type of the SSS^*^^ g rou P> the corallum is turbinate (figs. 99 and 105), the tabulae pass from side to side of the visceral chamber (fig. 98, c), and there is a well-marked fossula, while the septa extend inwards to near the centre of the coral. This large and important genus is represented by numerous species in the Silurian, Devonian, Fig. 104. Petraia calicula. Upper Silurian. Fig. I05.Zaphrentis StokesL Upper Silurian. and Carboniferous rocks. The Silurian and Devonian genus Petraia (fig. 104) has often been placed in the neighbour- hood of Zaphrcntis, but there is considerable uncertainty as RUGOSA. 213 to the forms which are really to be included under this head, and if the typical members of the genus are destitute of tabulae and dissepiments, it must then be rather referred to the Turbinolidce. In the genus Amplexus, which ranges from the Silurian to the Carboniferous, the structure of the coral- lum is essentially similar to that of Zaphrentis, but the septa are much less developed, and are so short as to leave the central portion of the tabulae smooth and bare. In Loplio- phyllum, of the Devonian and Carboniferous, the corallum essentially resembles Zaphrentis; but there is a flattened columella. In the Devonian Anisophyllum, again, there are three septa pre-eminently developed (fig. 100, B and c), and in Hallia (also Devonian), there is one such predominant septum, towards which a number of the septa are inclined. Lastly, in the Silurian Streptelasma, the tabulae are less developed than in Zaphrentis, and some of the septa are pro- longed inwards to the centre of the visceral chamber in the form of twisted plates. In the Cyathophyllince, in the second place, the septa are more or less regularly radiate in their arrangement (fig. 106), Fig. 106. A, Cross-section of Heliophyllum Halli, of the natural size Devonian ; B, Cross- section of a fragment of Cyathophyllum regium, of the natural size Carboniferous. and there is often no septal fossula. The corallum may be simple or compound, the tabulae are confined to a more or less extensive central area, and there is often an external zone of vesicular tissue formed by the great development of the dissepiments in this region. 214 RUGOSA AND ALCYONARIA. In Cyathopliyllum, the type- genus of the family, the coral- lum may be simple or compound, and the septa are well developed, some of them extend- ing to the centre of the visceral chamber, where they are twisted together to form a spurious colu- niella (fig. 106, B). The genus ranges from the Silurian to the Carboniferous. In Heliophyllum (figs. 106, A, and 107) the septa are provided with singular dissepi- mental outgrowths, which appear as so many spines or teeth on the free edges of the septa within Fig. 107. A young form of Helio- r phyttum Halli, viewed from one side. the CallCC, aild which glV6 them ' a characteristically cross -barred appearance in transverse sections. The genus is abundantly represented in the Devonian. Palceocyclns, which is exclusively Silurian, may be placed here in the meanwhile, though it is typically discoid in form, and has other peculiarities as well. The Silurian genus Omphyma is closely related to the simple forms of Cyathophyllum,. but the septa are divided into four groups by as many shallow depressions or fossulaa, and the coral- Fig. 108. Strombodes pentagonus. A Silurian Rugose Coral. Fig. 109. Strombodes gracilis. Silurian. lum is attached by root-like prolongations of the epitheca. In the genus Acervularia, again, of the Silurian and Devonian, we have forms in many respects resembling the compound species of Cyathophyllwn, but differing in the fact that each RUG OS A. 215 corallite possesses a central circular space, invested by a secondary and interior wall. Strombodes (figs. 108 and 109), of the Silurian, is very like Acermdaria, but the walls of the corallites are imperfectly developed, and the tabulae are funnel-shaped and invaginated in one another. Phillipsastrcea, again, approaches Strombodes in appearance, but the calices are not distinctly circumscribed (fig. 101); the walls of the coral- lites are deficient ; and the cor- allites are united by the fusion of their septa. The genus is Devonian and Carboniferous. As the type of another group of the Cyathophyllinoe, we may select the great genus Liiho- strotion (fig. 110), so highly characteristic of the Carbonifer- ous deposits in almost all parts of the world. The corallum in this genus is compound and fasciculate or massive, composed of cylindrical or prismatic corallites, which may or may not be in close contact with one another. The corallites possess a central tabulate area, which is traversed by a well-developed styliform coluniella. The genus Diphyphyllum, ranging from the Silurian to the Carboniferous, closely resembles the fasciculate forms of Lithostrotion, but the corallites have no coluniella. The Devonian genus Eridophyllum, again, differs from Diphy- phyllum, principally in the fact that the corallites are united by horizontal connecting-processes. Lastly, the genus Lons- daleia (figs. 74 and 111 A), of the Carboniferous rocks, presents some resemblance to the massive and astraeiform species of Lithostrotion, but the corallites have a secondary or inner wall, enclosing a central area, and the columella is formed of twisted lamellae. Lastly, we must mention here a great group of Cyatho- Fig 110. Fragment of a mass of Litlin- strotion irregulare, of the natural size. Carboniferous. (After De Koninck.) 216 RUGOSA AND ALCYONARIA. phylline Corals, which are characteristically Carboniferous in their range, and of which Clisiophyllum (fig. Ill, B) may be taken as the central type. In the forms in question (Clisio- pliyllum, Cydophyllum, Aidophyllum, Rlwdophyllum, &c.) the structure of the corallum resembles that of the simple forms of Cyathophyllum in the fact that there is a well-developed exterior zone of vesicular tissue ; but the axis of the visceral chamber is occupied by a series of more or less complicated structures, which represent a modification of the tabulate central area of Cyathophyllum, rather than a true columella. Fig. 111. A, Cross-section of two corallites of Lonsdaleia duplicata, Lower Carboniferous, enlarged ; B, Cross-section of the corallum of Clisiophyllum Keyserlingi, Lower Carbonifer- ous, of the natural size. (After James Thomson and the Author.) 4. Cystiphyllidce. In this, the last and most aberrant family of the Eugose Corals, the skeleton is usually simple, though occasionally compound ; and the septa are rudimen- tary, existing only as so many vertical striae or ridges within the calice (fig. 112). The outer wall is complete, but the entire visceral chamber is filled with small lenticular vesicles formed by a combination of dissepiments and tabulae. A distinct septal fossula is sometimes present. The family is Palaeozoic, and is confined to the Silurian and Devonian periods. In Cystiphyllum (fig. 112), the type-genus of the family, the corallum is usually simple, and the vesicular tissue of RUGOSA. 217 which it is made up, is often disposed in funnel-shaped layers. In most of the species the calice is open, but in one form (C. prismatic urn) the calice is closed by a lid or oper- cultim, consisting of four or more valves. In the genus Gfoiiiophyllum, of the Upper Silurian, a lid of four valves was present, and the extraordinary De- vonian genus Calceola (fig. 113), long referred to the Bracliiopoda, has been shown to be a coral of this family in which the calice is closed by an oper- culum consisting of a single piece. In this connection, it is worthy of notice that some of the living Alcy- onarian Corals (species of Primnoa, Paramuricea, and others) exhibit also a more or less complete operculurn. The calices of Cryptohelia pudica (one of the Hydroid group of the Stylasteridce) are also protected by a cal- careous lamina in front of each. Before leaving the Cys- tiphyllidce, a few words may be said as to the singular and problematical fossils termed Beatricea, which, so far, are only known as occurring in the Lower Silurian of North America. In these extra- ordinary forms (fig. 114) we have bodies of great size, Fig. Il2.Cystiphyllum vesiculosum, showing a succession of cups produced by budding from the original coral. One side of the calice is broken away, and shows the internal structure. Of the natural size. Devonian, America and Europe. (Original.) 218 RUGOSA AND ALCYONARIA. often many feet in length, of more or less cylindrical form, and principally composed of a calcareous vesicular tissue, essentially similar to that of Cystiphyl- lum. In the centre is what appears to represent a tabulate area, such as we meet with in many of the Cyathophyllidce. If truly corals, these huge fossils must be regarded as very aberrant members of the Cystipliyllidce ; but there is some reason for thinking that Beatricea is per- haps really founded upon peculiar forms of Stromatoporoids. Fig. 113. Calceola san alina. An operculate Ru- gose Coral. Devonian. Fig. 114. Beatricea undulata. A, Diagram showing the internal structure as exhibited by a longitudinal section ; B, Portion of the base of a specimen from the Hudson River forma- tion (Lower Silurian), the real length of the portion figured being about two feet. (After Billings.) ORDER III. ALCYONARIA. The Alcyonarian Zoophytes are Actinozoa in which the. polypes possess eight tentacles, which are fringed on their sides with lateral pinnce or papillce, hence the name of OctocoraUa often applied to the order. Almost all the members of the order are composite, the tubular polypes being united by a ccenosarc, through which ramify canals by which their body- cavities are placed in communication. Of the living groups of the Alcyonaria, the " Organ-pipe Corals" (Tuliporidce) have a well -developed sclerodermic ALCYONARIA. 219 compound corallurn, but they are unknown in a fossil con- dition. In the Alcyonidce the skeleton consists simply of calcareous spicules scattered in the soft parts, and the family is almost, unknown in the fossil condition. A species of Alcyonium, however, has been recognised in tjie Pliocene (Red Crag) of Britain. In the Pennatulidce (the " Sea-rods " and " Sea-pens "), besides detached spicules, there is a skeleton in the form of a horny or calcareous rod, supporting the soft colony. The Silurian genus Protovir- gularia was believed to belong to the Pennatulidce, but it is certainly not of this nature, and is probably a Graptolite. The family has, indeed, no certain fossil representatives till we reach the latest Secondary or earliest Tertiary deposits. In the Pisolitic Limestone (late Cretaceous) of France, we have the genus Pavonaria ; while Graphularia occurs in the Eocene, and the Miocene Tertiary has yielded examples of Graplmdaria, Virgularia, and Ccelographula. In the family of the Gorgonidce (" Sea-shrubs ") there is a branched sclero- basic corallum, the surface of which is grooved or sulcate. The corallum may be horny or calcareous, or it may be composed of alternating calcareous and corneous segments (as in Isis and Mopsea}. The earliest representatives of the Gforgonidce so far as we have any sufficient evidence are found in deposits of the age of the Eocene Tertiary, the genera Mopsea and Websteria occurring in the London clay. The genus Coralliwn, embracing the living Eed Coral, has been quoted from the Jurassic and Cretaceous, and un- doubtedly occurs in the Miocene Tertiary ; and deposits of the same age have yielded species of Isis, Gorgonia, and Melitlma. So far as all the preceding forms are concerned, it will be seen that the Alcyonaria, though widely distributed in existing seas, are of little geological importance, and are, moreover, comparatively of modern origin. Mr Moseley, however, has shown that the living corals of the genus Heliopora are truly referable to the Alcyonaria, and not to the Zoantharia, in which they had been previously placed : and he has further shown that the large and ancient group of fossil corals of which Heliolites is the central type, is 220 RUGOSA AND ALCYONARIA. essentially similar to Heliopora in structure. We thus are presented with a new family of the Alcyonaria that of the Helioporidce which has played no inconsiderable part in geological history. The Helioporidce were formerly placed in. the " Tabulate " section of the Zpantharia sclerodermata, and possess a ^vell-developed sclerodermic corallum, composed of tabulate tubes of two sizes, the larger ones being furnished with rudimentary septa. In the living Reliopora ccerulea (fig. 115) the corallum is composite and sclerodermic, and is Fig 115. A, Portion of the corallum of Heliopora ccerulea, of the natural size (after Milne- Edwards); B, Portion of the surface of a branch of Heliopora ccerulea, magnified eight diameters (after Moseley) ; c, c, c, the openings (" calices ") of the corallites, surrounded by the smaller tubes of the coenenuhyma. composed of corallites united by what has usually been regarded as a " ccenenchyma." The corallites are tubular, crossed by well-developed tabulae, and having their walls folded in such a manner as to give rise to a variable number (generally twelve) of septal laminae. The coenenchyma, so called, is composed of slender tubes, of smaller size than the true corallites, packed closely side by side, crossed, like the corallites, by regular transverse tabulae, but destitute of septa. The soft parts occupy only the parts of the corallum above the uppermost tabulae, and therefore only a surface- layer of the colony is actually alive. The polypes are com- pletely retractile, with eight pinnately-fringed tentacles, and eight mesenteries. The mesenteries, however, have no cor- respondence with the septa, which are twelve in number as ALCYONARIA. 221 a rule. The septa are thus seen to be pseudo-septa, and they cannot be regarded as being homologous with the septa of the Zoantharia sclerodermata. The so-called ccenenchyrual tubes are occupied by sacs lined by the endoderm, which are closed externally, but communicate freely with the body- cavities of the polypes by means of transverse canals ; and Mr Moseley suggests, with great probability, that these are really of the nature of rudimentary sexless polypes. The genus Heliopora is not known as occurring in the fossil condition, but it is represented by various extinct types, dating from the Lower Silurian period. Of the extinct types, the Silurian and Devonian genus Heliolites (fig. 116) is the most important. It has a well- Fig. 116. A, Small colony of Heliolites megastomc, of the natural size ; B, Small portion of the surface of the same, magnified, showing the calices (a) and the mouths of the ccenen- chymal tubes (/>) ; c, Vertical section of the same, enlarged, showing the tabulate corallites (a), and the tabulate tubes of the coeuenchyma (ft). (Original.) developed sclerodermic corallum, with comparatively large- sized, tubular, regularly tabulate corallites, usually possess- ing distinct but rudimentary septa, intermingled with a copious ccenenchyma formed of tabulate geometric tubuli, much smaller than the corallites, and destitute of septa. The so-called " coenenchymal " tubules were probably occu- pied in the living state by rudimentary or imperfect polypes. 222 RUGOSA AND ALCYONARIA. In the Silurian Plasmopora, the corallum is very similar to that of Heliolites, but the coenenchyma is more vesicular, and its tubules are not so distinct. The g % enus Propora, also Silurian, is very like the preceding, but the calices are exsert. Lastly, we may mention the genus Polytremacis, which hardly differs from Heliolites, save in its granular surface, and which is remarkable in being found in rocks as modern as the Cretaceous. LITERATURE. [In the subjoined list of some of the more important works treating of the fossil corals, no distinction has been made as regards the different orders, since most works of the kind quoted deal with members of two or more of the orders.] 1. " Manuel d'Actinologie et de Zoophytology." De Blainville. 1834-37. 2. " Klassen und Ordnungen des Thier-Reichs," vol. ii. ' Strahlen- thiere.' Bronn. 1859-60. 3. " Histoire des Animaux sans Vertebres," vol. ii. Lamarck. (Ed. 2, 1836.) 4. " Histoire Naturelle des Coralliaires on Polypes proprement dits." Milne-Edwards. 1855-60. 5. " Zoophytes." * Report of Exploring Expedition under Captain Wilkes.' Dana. 1848. 6. " Polypiers Fossiles des Terrains Paleozoiques." Milne-Edwards and Haime. 7. "Monograph of the British Fossil Corals." ' Palaeontographical Society.' Milne-Edwards and Haime. 8. " British Fossil Corals." (Supplement to the preceding.) ' Palse- ontographical Society.' Martin Duncan. 9. " Introduction a 1'etude des Polypiers Fossiles." Fromentel. 1858-61. 10. "Reports on the British Fossil Corals." < Rep. Brit. Assoc.,' 1869-71. Martin Duncan. 11. " On the Affinities of the Palaeozoic Tabulate Corals with Existing Species." ' Amer. Journ. Sci. and Art,' 1872. Verrill. 12. " Affinities of the Anthozoa Tabulata." ' Ann. of Nat. Hist,' ser. 4, vol. xviii. 1876. Lindstrom. 13. " Monographic der Sclerodermata Rugosa aus der Silur-formation Estlands," &c. Dybowski. 1873. 14. " Beitrage zur Kenntniss Fossiler Korallen." ' Deutsch. GeoL Ges.' 1870. Kunth. 15. " Guynia and Haplophyllia." Phil. Trans.,' 1872. Martin Duncan. 16. " Corals." ' Encyclopaedia Brit.' 9th ed., vol. vi. 1877. Nicholson. ALCYONARIA. 223 17. " Contributions to the Study of the Chief Generic Types of Palae- ozoic Corals." 'Ann. Nat. Hist.' 1875-76. Thomson and Nicholson. 18. "First Report on the Palaeontology of the Province of Ontario." 1874. Nicholson. 19. " Fossil Corals of the State of Michigan." 1876. Rominger. 20. " British Palaeozoic Fossils." 1851. M'Coy. 21. "Petrefakten Deutschlands." 1826-33. Goldfuss. 22. " Nouvelles Recherches sur les Animaux Fossiles du Terrain Car- bonifere de la Belgique." Premiere Partie. 1872. De Koninck. 23. "On the Structure and Relations of the Alcyonarian Heliopora cserulea," &c. ' Phil. Trans.,' vol. clxvi. 1876, Moseley. 224 CHAPTER XII. SUB-KINGDOM IILANNULOIDA. ECHINODERMATA. SUB-KINGDOM III. ANNULOIDA. Animals in which the ali- mentary canal is completely shut off from the general cavity of the body. Nervous system distinct. A peculiar system of canals, usually communicating with the exterior and containing water derived from the outside, and termed the " water-vascular " or " aquiferous " system, is present in all. In none is the body of the adult composed of definite segments, or provided with " bilaterally disposed successive pairs of appendages!' This sub-kingdom was proposed by Huxley, as a pro- visional arrangement, to include the two groups of the Echino- dermata (Sea-urchins, Star-fishes, &c.) and the Scolecida (Tape- worms, Bound-worms, Wheel -animalcules, &c.) Whether this arrangement be ultimately retained or not, matters not at all to the palaeontologist, as no member of the Scolecida is known in the fossil condition. The palaeontologist, therefore, has simply to deal with the Echinodermata, the complete dis- tinctness of which, as a group, is beyond question. CLASS ECHINODERMATA. The class Echinodermata comprises the animals known commonly as Sea-urchins, Star-fishes, Brittle-stars, Sea-lilies, and Sea-cucumbers, and is distinguished by the fact that the external envelope of the body (" perisome ") has the power of ECHINODERMATA. 225 secreting calcareous matter to a greater or less extent. The integument is, therefore, either composed of calcareous plates articulated together, or is coriaceous, and has granules or spic- ules of lime developed in it. The water-vascular system usually communicates with the exterior, and generally subserves locomo- tion. The adult animal exhibits more or less distinctly a "radial symmetry',' or star-like arrangement of its parts, but the young animal is more or less bilaterally symmetrical. The Echinodermata are divided into the following seven orders : 1. Echinoidea. Ex. Heart-urchin (Spatangus). J >i/Vt ^~~ 2. Asteroidea.Ex. Star-fish (Uraster). (//' / 3. Ophiuroidea. Ex. Brittle-star (Ophiura). ^ Crinoidea. Ex. Stone-lily (Encrinus). 5. Cystoidea. Ex. Hemicosmites. . Blastoidea.Ex. Pentremites. 7. Holothuroidea. Ex. Trepang (Holothuria). The above is not a true or natural arrangement of the orders of the Echinodermata, but it is convenient for many reasons to consider them in this sequence. As regards the general distribution of the class, the Echinodermata are rep- resented more or less abundantly in all the great formations from the Upper Cambrian to the present day. The orders Cystoidea and Blastoidea are not only extinct, but are ex- clusively Palaeozoic ; while in the Crinoidea we have an order which has passed its prime, and appears to be verging on extinction. On the other hand, the orders Echinoidea, Aster- oidea, Ophiuroidea, and Holothuroidea appear to have attained their maximum of development at the present day. The Asteroidea and Ophiuroidea commence in the Silurian period. The Echinoids commence in the Upper Silurian, but reach no marked development till we enter upon Mesozoic deposits. Lastly, the Holothurians, as might be expected from the soft nature of their integuments, are hardly known as fossils, though they seem to have existed at any rate as early as the Carboniferous period. \^ - VOL. I. f> O*^ 1 226 ANNULOIDA. ORDER I. ECHINOIDEA. The members of this order commonly known as Sea- urchins are characterised by the possession of a more or less globular, heart-shaped, discoidal or depressed body, encased in a " test " or shell, ivhich is composed of numerous calcareous plates, immovably connected together. The intestine is convoluted, and there is a distinct anus. The mouth is usually armed with calcareous teeth, and is always situated on the inferior aspect of the body, but the position of the vent varies. As a matter of course, the palseontological student has to deal with nothing except the test of the Echinoids and its Fig. 117. Morphology of Echinoidea. A, Young specimen of Strongylocentrotus Drobacli- iensis, viewed from above. B, Small portion of the test of the same, magnified, c, Summit of the test of Echinus sphcera, magnified. D, Clypeaster subdepressus, viewed from above, showing the petaloid ambulacra. E, Spine of Porocidaris purpurata. F, Pedicellaria of Tox- opneustes lividus. a, a, Ambulacral areas ; I, i, Interambulacral areas ; g, Genital plate ; o, Ocular plate ; ra, Madreporiform tubercle ; p, Membrane surrounding the anus. (Figs. A, B, fyid D are after A. Agassiz.) appendages, and these must be described in some detail. The " test " of the Echinoidea may be regarded as essentially composed of the so-called " corona " and of the " apical disc/' ECHINOIDEA. 227 though other less important elements are present as well. The " corona " is the main element of the test, and includes all the calcareous covering of the animal except the scat- tered plates round the mouth and anus and the "apical disc." The test is composed of numerous calcareous plates, firmly united to one another by their edges, arranged in rows (fig. 117, A), and bearing different names, according to their posi- tion and function. In the curious Urchins which form the family of the Echinotlmridce, and in some of the Palaeozoic Echinoids, the plates of the test overlap one another in an imbricating manner, so that the shell becomes flexible. As a rule, however, the corona forms an immovable case or box, within which the animal is contained ; and its growth is carried on by means of additions made to the edge of each individual plate, by means of an organised membrane which Fig. 118. Morphology of Echinoidea. A, Portion of the test of Galerites hemisphericus, en- larged, showing an inter-ambulacral area (a), and an ambulacral area (ft). B, Genital and ocular disc of Hemicidaris intermedia, enlarged : c, Ocular plate; d, Genital plate; e, Anal aperture ; /, Madreporiform tubercle. (After Forbes.) passes between the sutures, or the lines where the plates come in contact with one another. In all recent and most fossil Echinoids, the test is com- posed of twenty meridional rows of calcareous plates, which are arranged in ten alternating zones or areas (fig. 117, A).' Each zone, therefore, is composed of two rows of plates. In five of these zones (figs. 117, B, and 118) the plates are of large size, and are not perforated by any apertures. These 228 ANNULOIDA. zones are called the " interambulacral areas." The remaining five zones alternate with the former, and are composed of very much smaller plates, which are perforated by minute apertures or pores. Through these apertures are emitted the little suctorial tubes of the water-vascular system the so- called " ambulacral tubes " or " tube - feet " by means of which the animal moves. Hence these zones of perforated plates are termed the " ambulacral areas " or " poriferous zones." In one great group of the Echinoids the ambulacral areas pass from the centre of the base of the shell to its summit (figs. 117, A, and 119), when they are said to be "perfect" (ambulacra perfecta) or " simple." In another great group Fig. 119. Galerites albogalerus. The first figure shows the under surface with the mouth and anus ; the middle figure is a side view ; and the right-hand figure shows the upper surface, with the ambulacral areas converging to the apical disc. White Chalk. the ambulacral areas are not thus continuous from pole to pole, but simply form a kind of rosette upon the upper surface of the shell (figs. 117, D, and 120). In these cases Fig. 120. Scutella subrotunda, showing petaloid ambulacra. Miocene. as in the common Heart-urchins the ambulacral zones are said to be " circurnscript " (ambulacra circumscripta) or " petaloid." The most important external structures of the corona are EOHINOIDEA. 229 the tubercles and spines. The tubercles are rounded eleva- tions upon which the spines are carried (figs. 117, A, and 121). They vary much in their dimensions, and receive special names, according to their size or position on the test. Ordinarily the tubercle consists of a rounded ball or hemi- sphere (the " mamelon ") supported upon a conical process (the " boss ") which arises from the plate. The ball of the tubercle may or may not be perforated for the insertion of a ligament which is attached to the articular surface of the spine. In many cases (as in fig. 121) the base of the tu- bercle is surrounded by a round or oval, smooth and excavated space which is termed the " areola " or " scrobicule." Fig. 121. Hemicidaris crenukiris, showing tubercles, the larger of which are perforated, and are surrounded by an areola. Oolite. The spines are movable appendages which are jointed to the tubercles by a sort of " ball-and-socket " or " universal " joint. They are used defensively and in loco- motion, and vary much in length and shape. Sometimes they are very minute ; at other times they attain a length considerably exceed- ing the diameter of the test. Sometimes they are slender, tapering, and truly spine-like (fig. 1 1 7, E) ; at other times they are thickened, ovate, or almost globular (fig. 122). The spine fits on to the rounded head of the tubercle by a concave articular surface (" acetabulum "), and there may or may not be a pit at the bottom of this, for the attachment of the ligament before spoken of. Above the acetabulum or socket of the spine there is a prominent ridge or ring, more or less " milled," Fig. 1-2-2. Spine of Cidaris glan- diferus. 230 ANNULOIDA. for the attachment of the muscular fibres which move the spine. The " apical disc " or " genital disc " occupies the summit of the test, and is generally composed of ten plates (figs. 117, c, and 118, B). Five of these plates are of comparatively large size, and are termed the "genital plates," each being- perforated by the duct of an ovary or testis. Each genital plate occupies the summit of one of the interambulacral areas. One of the genital plates (the right antero-lateral plate) is larger than the others, and supports a spongy tubercle, perforated with many apertures, like the rose of a watering-pot, and termed the " madreporiform tubercle " (fig. 118, B). This structure protects the mouth of the canal by which water is admitted from the exterior to the water- vascular system. Wedged in between the genital plates, and occupying the summits of the ambulacra! areas, are five smaller, heart-shaped, or pentagonal plates, each of which is perforated for the reception of an " ocellus " or eye, and which are therefore termed the " ocular plates." The EcJiinoidea may be divided into the four groups of the Eegular Echinoids, the EchinotJmridce, the PeriscJioecki- nidce, and the Irregular Echinoids ; and we may briefly consider the more important characters, the geological range and the leading type of these divisions. I. EEGULAR ECHINOIDS (EcJiinoidea endocyclica). In this group of the Echinoids the mouth is situated in the centre of the base (fig. 123), and the vent is placed at the summit ^^^^^^^^ Fig. 123. Salenia penottata, t "regular" Echinoid. The left-hand figure represent* the upper surface of the shell, and shows the anus surrounded by the apical disc. The right- hand figure shows the mouth in the centre of the base. of the test, surrounded by the genital disc. They have a test which is almost always circular, or spheroidal, or, it may be, depressed ; and the mouth is armed with a complicated ECHINOIDEA. 231 masticatory apparatus. The Regular Echinoids comprise the families of the Cidaridce, Hemicidaridce, Diademadce, Echin- idce, and Saleniadce. In the Cidaridce, the test is spheroidal and more or less ilattened at the oral and anal poles. The ambulacral areas (fig. 124), are very narrow, often flexuous, and never pro- vided with large tubercles. The interambulacral areas are wide, and carry large perforated tubercles, surrounded by an areola, and supporting the primary spines. The spines are of two sizes, the primary ones usually more or less cylindrical, clavate, or fusiform, and generally longi- tudinally ridged or tuberculate (fig. 122). Of the genera of this family, Cidaris itself (fig. 124) is the most important, ranging from the Trias to the present day. Rhabdocidaris is Jurassic and Cre- f p -. 12 ? u ? d ? surfa f c ' of the + tes * of Cidaris vcsiculosa, of the natural taceous ; Diplocidaris is Jurassic ; size, chalk. (After Wright.) and the Porocidaris of the Secon- dary and Tertiary periods has now been detected by Sir Wyville Thomson in a living condition. In the Hemicidaridce (fig. 121) the test is spheroidal, more or less depressed, and with a close general resemblance to that of the Cidaridce. The ambulacral areas, however, though narrow and mostly undulated, are wider than in the Cidaridce, and are provided with comparatively large tuber- cles, which may be developed inferiorly only (Hemicidaris), or which may extend along the entire length of the area (Acrocidaris). The interambulacral areas are wide, and carry very large perforated tubercles with crenulated bosses. The spines are usually long, cylindrical, and tapering. The type- genus of this family is Hemicidaris (fig. 121), which ranges from the Upper Trias to the Lower Cretaceous inclusive. In Acrocidaris, of the Jurassic period, the ambulacral areas are comparatively wide. In the family of the Diademadce sometimes made to include that of the Hemicidaridce the test is circular or 232 ANNULOIDA. pentagonal, more or less depressed and flat below. The ambulacral areas are wide, and carry two rows of large primary tubercles (fig. 125), equal in size to the two or more rows of tubercles upon the interambulacra. The tubercles are sometimes perforated, sometimes imperforate, and they may or may not be crenulated. The spines are cylindrical Fig. 125. Portion of the test of Pseiulodiadema Fittonii, enlarged four times, a, Ambul- acral area ; i, Interambulacral area. Lower Greensand (Cretaceous). (After Wright.) and slender, and usually of considerable length. In the living Diadema and in Astropyga the spines are long, tubu- lar, and covered with imbricated scales arranged in oblique rings. As the type of the family we may take Pseudodia- dema, which ranges from the Liassic to the Tertiary inclusive, and in which the spines are solid and microscopically striated, while the tubercles are perforated (fig. 125). In the Cretace- ous Cyphosoma the tubercles are solid. Hemipedina, again, of the Oolites, is very like Pseudodiadema, but the tubercles are Fig. 126. Goniopygus iruijor, viewed from above and sideways, of the natural size. Cretaceous. not crenulated. We may also place here the Cretaceous genus Goniopygus (fig. 126), which presents us with a type intermediate between the Diademadce and Saleniadce. It ap- proaches the latter family more particularly in the great size ECHINOIDEA. 233 of the apical disc ; but this structure is only composed of the normal ten plates, and wants the supernumerary or " sur- anal " plate of the Saleniadce. In the family of the Saleniadce the test is generally spher- oidal, hemispherical, or depressed, and the ambulacral areas are always narrow, sometimes straight, sometimes flexuous, and without large primary tubercles. The interambulacral areas are always provided with two rows of large tubercles, with crenulated bosses, which may or may not be perforated. The leading character of the family, however, is to be found in the apical disc (figs. 123 and 127), which is of unusually large size, and possesses a super- numerary or " suranal " plate in addition to the ten normal plates. This suranal plate (fig. 127, s) is placed in front of the anus, and it may be single, or it may be broken up into several (not more than eight) elements. Of the genera of the Saleniadce, Acrosa- lenia is essentially Jurassic ; Pel- tastes and Goniophorus are Cre- taceous ; and Salenia itself (fig. 123), commencing in the Creta- ceous, is not only found in the Tertiary rocks, but has now been detected in a living condition. Lastly, in the great family of the Echinidce the test is usually globular or hemispherical ; and the ambulacral areas are comparatively wide, and always carry two or more rows of tubercles. The interambulacral areas are wide, and carry primary tubercles, which are always imperforate, and are never of very large size. The spines are short and awl- shaped, and their surface is marked with fine longitudinal lines. Of the genera of this family, Glypticus, Magnotia, Polycyphus, the great group termed Stomechinus, and others, occur in the Jurassic ; Codiopsis is Cretaceous ; and Tern- nechinus is Tertiary and Kecent. II. ECHINOTHUIIIDJS. In this small but highly remark- Fig. 127. Apical disc of Peltastcs Wrighlii, one of the Sakniadce. a, Anus ; g, One of the genital plates ; o, One of the ocular plates ; s, Suranal plate. Twice the natural size. Cre- taceous (Lower Greensand). (After Wright.) 234 ANNULOIDA. able division of the Echinoidea the test is "regular," the anus being placed in the centre of the apical disc, and the ambulacral areas being continuous ; but the plates of both the ambulacral and interambulacral areas are imbricated and overlap one another (fig. 128), the test thus becoming flexible. In this abnormal character, the Echinothuridce agree with some of the Palaeozoic Urchins, but they differ from these, and agree with the ordinary Eegular Echinoids in having the test composed of no more than twenty rows of plates. Fig. 128. Portion of one of the ambulacral areas of Ecldnotliuria floris, enlarged four times. Chalk. (After Wright.) The only fossil forms of this group, as yet discovered, are referable to the Cretaceous genus Echinothuria, the true affinities of which have now been elucidated by the dis- covery of the extraordinary living types referred to the genera Calveria (or Asthenosoma) and Phormosoma. III. PERISCHOECHINID^E. In this group we have a series of singular Palaeozoic Sea-urchins, which agree with the two preceding sections in having a "regular" test, but which differ from all known Echinoids, living or extinct, in having the test composed of more than twenty rows of plates. The test is still divided into five ambulacral and five interam- bulacral areas, but there is a multiplication of the rows of plates in either the ambulacra or interambulacra, or in both. The apical disc consists of no more than the normal ten plates, and the anus is placed in its centre. The ambulacral areas are continuous from pole to pole. In the genus Palcecliinus (fig. 129) the test is spheroidal, and its plates abut against one another without any over- ECHINOIDEA. 235 lapping. The ambulacral areas are comparatively narrow, of two rows only, each plate perforated by two pores. The in- terambulacral areas are broad, and are composed of from five Fig. 129. Palaxhinus ellipticiis. The left-hand figure shows a portion of an ambulacral area enlarged. The right-hand figure exhibits a single interambulacral plate. to eight rows of plates. The apical 'disc (fig. 130, A) has five triply-perforated genital plates, and an equal number of doubly-perforated ocular plates (Baily), but the latter are not recognised by De Koninck. The genus is said to occur in the Silurian, but is principally known as occurring in the Carboniferous rocks. Fig. 130. A, Apical disc of Palcechimis, enlarged (after Baily). B, Apical disc of Melonites (after Meek and Worthen) : g, One of the genital plates ; o, One of the ocular plates. The genus Eocidaris, of the Devonian, Carboniferous, and Permian formations, also appears to have rigidly articulated plates. The interambulacra are of five or more rows, some 236 ANNULOIDA. of which disappear before reaching the poles. Each inter- ambulacral plate carries a primary tubercle, not surrounded by a ring. The ambulacral areas are composed of two rows of plates. In the genera Melonites and Oligoporus, of the Carboniferous rocks, we have large spherical Urchins, in which the test appears to have been rigid, though some of the plates are occasionally bevelled off, so as to articulate in an over- lapping manner with one another. In Melonites (fig. 131) there is a multiplication of the plates of both the interam- bulacral and ambulacral areas, the former consisting in the middle of about nine rows, while the latter are of eight rows, Fig. 131. A, Portion of an ambulacral area of Melonites multiporus. B, Portion of an ambulacral area of Oligoporus Dance : i, Lateral row of interambulacral plates. Carbon- iferous. (Meek and Worthen). or, in a British species, of from twelve to fourteen rows. The central two rows of ambulacral plates are larger than the rest and elevated above them, and each plate of these areas is doubly perforated. The apical disc (fig. 130, B) is composed of the normal ten plates, but the ocular plates are sometimes imperf orate, and the genital plates are fur- nished with from three to five pores. ECHINOIDEA. 237 Olif/oporus (fig. 131, B) is very similar to Melonites, but the ambulacral areas consist each of only four rows of plates. In the genus Archceocidaris, well known as a Carbon- iferous type, the test is spheroidal, the ambulacra are only two-rowed, and the interambulacra are wide, and are com- posed of three or more rows of plates. The interambulacral plates carry each a large perforated primary tubercle, and have the curious character, as shown by Mr John Young, that some of their edges are bevelled off, this clearly ap- pearing to indicate a certain amount of flexibility in the test, similar to what we have seen in the group of the EcMnothuridce. A much nearer approach to the type of the Echino- tlmridce, however, is made by some other genera of the Pcrischoechinidce. In the forms in Question (Periscliodo- mus, Lepidechinus, &c.) the plates of the test overlap one another in an imbricating manner, as in the recent Calveria, and the test must have been quite flexible. In the Echino- thuridce, however, the imbrication of the interambulacral plates is from above downwards, and that of the ambulacral plates from below upwards, exactly the reverse of this arrangement taking place among the flexible Perischoechinids. Moreover, the former have only twenty rows of plates in the test, whereas this number is exceeded in the latter. In the Carboniferous Perischodomus there are two rows of am- bulacral and five rows of interambulacral plates, and in the nearly allied Lepidechinus, of the Devonian and Carboniferous, there are as many as eleven rows of interambulacral plates. The Carboniferous genus RhoecJiimcs is very nearly allied to the two preceding, but the interambulacral plates have no primary tubercles. Lastly, in the Carboniferous Lepidestlies we have another flexible Perischoechinid, with imbricated plates, but the ambulacra were composed of no less than ten rows of plates, and the interambulacral areas are comparatively narrow, and are composed of several rows of plates. IV. IRREGULAR ECHINOIDS (Echinoidea exocyclica). In this section of the Echinoidea the test is generally of an oblong, 238 ANXULOJDA. pentagonal, heart-shaped, or discoidal figure (as in the com- mon " Heart -urchins" and " Cake -urchins ") ; the anus is situated outside the apical disc, usually marginal or submar- ginal in position ; there are mostly only four genital plates in the apical disc ; and the mouth is mostly destitute of Fig. 132. Discoidea cylindrica, an "irregular" Echinoid. The right-hand figure shows the summit of the shell, with the genital disc. The left-hand figure shows the base of the shell, on which are situated both the mouth and anus. Cretaceous. a masticatory apparatus. The Irregular Echinoids may be divided into the families of the Echinoconidce, Collyritidm, Echinonidce, Echinobrissidce, Echinolampadce, Clypeastridw, Ananchytidm, and Spatangidoe. In the Echinoconidce the test is usually circular or pen- tagonal, the ambulacral areas narrow, and the plates of both Fig. 133. Pygaster truncatus, viewed from above, from behind, and from one side. Cretaceous. areas carrying small, crenulated, and perforated tubercles. The mouth is inferior and central in position, toothed ; the vent is on the upper surface, marginal, or inferior ; the apical disc central, superior, and composed of the normal ten plates. The spines are short and awl-shaped. All the members of this family are found in the Oolitic and Cretaceous rocks. The genus Pygaster (fig. 133) commences in the lowest Jurassic deposits, and extends upwards into the ECHINOIDEA. 239 Cretaceous. It is easily recognised by the great size of the anal aperture, which is oblong or pyriform in shape, and is placed upon the upper surface of the test. The genus Hybo- (fig. 134), again, is an aberrant type, since the mouth, Fig. 134,Hy'bnclypns gilberulus, viewed from above, from one side, and from below. Jurassic. though inferior, is not central ; the opening of the anus is placed in a longitudinal dorsal valley ; and the posterior two ambulacral areas are disjoined from the anterior three, con- verging (as in the Collyritidce) to two distinct points upon the upper surface of the test. Of the remaining genera of this family the two most important are Galerites (fig. 119) and Discoidea (fig. 132), constituting two nearly related types which are widely distributed in the Cretaceous rocks. Holec- typus (fig. 136, A), lastly, is closely allied to Discoidea, and is principally confined to the Jurassic period. In the small and singular family of the Collyritidce (fig. 135), the test is usually ovate or heart-shaped; the ambu- lacral areas are narrow, and are " disjunct," meeting at two Fig. 135. Collyrites (Disaster) Ewle$i t viewed from above, from one side, and from below. Jurassic. more or less remote points upon the upper surface ; and the tubercles are small, perforated, and crenulated. The mouth is inferior and excentric ; the anus is supra-marginal ; and the elements of the apical disc are detached. This family is 240 ANNULOIDA. wholly confined to the Jurassic and Cretaceous rocks, and by far the most important genus contained in it is Collyritcs (Disaster or Dysaster) itself. In the small family of the Echinonidce the test is oval, the ambulacral zones meeting at the apical disc, and the tubercles neither perforated nor crenulated ; this last char- acter separating the family from the Echinoconidce. There are only four genital plates in the apical disc ; the mouth is inferior, central, and toothless ; and the anus is usually supra-marginal. The only fossil genus is the Pyrina of the Cretaceous rocks. In the family of the Echindbrissidce (Cassidulidce in part) the shape of the test is variable ; the tubercles are small, imperforate, un crenulated, and surrounded by sunken areolce; the spines are short and slender ; and the ambulacral areas are petaloidal, lanceolate above, or sub - petaloidal. The mouth is inferior, sub-central, and edentulous ; and the anus (fig. 136, B) is dorsal, opening in a valley, or supra-marginal. Fig. 136. A, Holectypus Jiemisphericus, viewed from above Jurassic (after Edward Forbes) ; B, Echindbrisms clunicularis, viewed from above Jurassic (after Wright). Besides the living Nudeolites, the family comprises a large number of Jurassic, Cretaceous, and Tertiary Urchins, be- longing to the genera Echinobrissus (fig. 136, B), Clypeus, Catopygus, Pygaulus, &c. In the family of the Echinolampadce (Cassidulidce in part) we have Urchins in many respects agreeing with the Echino- Irissidce, especially in their petaloidal or sub-petaloidal am- bulacra, but having the anus marginal, infra-marginal, or supra-marginal, in no case opening into a dorsal sulcus. ECHINOIDEA. 241 Moreover, the ambulacral zones are expanded and petaloid in the immediate neighbourhood of the mouth, and so form an " oral rosette " in the centre of the base, while the tuber- cles are often perforated. Of the more important genera of this family, Pygurus is Oolitic and Cretaceous, Conoclypus and Echinanthus are Cretaceous and Tertiary, and Echino- lampas is Tertiary and Recent. In the family of the Clypeastridce the test is usually circular or elliptical, generally depressed, the surface covered with small tubercles surrounded by sunken, ring-like arcolce, and carrying hair-like spinqs. The dorsal portions of the ambulacral zones are wide and petaloid, and the ambulacral pores are confined to the apical " rosette " thus formed. The mouth is inferior, central, and armed with teeth ; and the anus is marginal or infra-marginal. The numerous types included in this family range from tho Cretaceous to the present period, the most important genera being Clypeaster, Scutella (fig. 120), Echinocyamus, and Echinarachnius. In the family of the Ananchytidce ( = Echinocoridce, Wright) the test is usually ovate or heart-shaped, the mouth is tooth- less, excentric, and advanced forward, and the anus is mar- ginal, infra-marginal, or supra-marginal (fig. 137, B). The ambulacral areas are not petaloidal, and the ambulacral pores are not confined to a dorsal rosette. There are four genital pores in the apical disc ; the tubercles are small, perforated, and crenulated ; and the spines are minute. The chief genus of this family is Ananchytes itself (fig. 137, B), represented by many forms in the Cretaceous rocks. Holaster, abundantly represented in the Cretaceous, is very nearly allied to Ananchytes, but has the anus supra-marginal. In Cardiaster, again, which is also Cretaceous, there is the additional character of the existence of a " fasciole," which passes beneath the anus and is continued on the sides of the test. As will be seen immediately, the presence of " fascicles " that is to say, of circumscribed bands of micro- scopic granules, occupying definite areas and positions on the test is highly characteristic of the Spatangidce, towards which Cardiaster thus makes an approach. Lastly, in the family of the Spatangidce or Brissidce VOL. I. Q 242 ANNULOIDA. (" Heart-urchins ") the test is oval, oblong, or commonly heart-shaped; the ambulacra (fig. 137, A) are petaloid, the anterior one unpaired, usually lodged in a groove or " sul- cus," and thus rendering the skeleton bilaterally symmetrical. ^..*;*;ii -.:^:-'* 3' :- -"V^ S ^ iiil ; i^ Fig. 137. A, Upper surface of Micraster coranguimim, of the natural size Cretaceous ; B, Under surface of Ananchytes ovata, of the natural size Cretaceous. (After Edward Forbes.) The anus is posterior and supra-marginal. The mouth is inferior, eccentric, and toothless. The tubercles are small, and support hair-like spines, but there are larger, crenulated, and perforated tubercles for supporting larger spines. As a rule, bands of microscopic tubercles known as "fascicles" (fig. 138) are present, and oc- cupy different positions in dif- ferent genera. Sometimes the " fasciole " surrounds the am- bulacral rosette, when it is said to be " peripetalous ; " some- times it is " internal," sur- h Mt d rounding the unpaired ambu- lacrum; sometimes it surrounds the sides, and is said to be " lateral ; " at other times it runs round the test, and is termed "marginal;" and lastly, it may be limited to the base of the anal aperture, when it is termed " sub-anal." Of the hand figure shows the " fasciole " cutting the ambulacral rosette. ECHINOIDEA. 243 genera of the Spatangidce, Micraster (fig. 137, A), Echino- spatagus, Epiaster, and others are Cretaceous ; Hemiaster and Periaster are both Cretaceous and Tertiary ; Gualtieria (fig. 138), Macropneustes and Pericosmus are Tertiary; and Spat- angus, Schizaster, Eupatagus, JBrissus, and Brissopsis are repre- sented both in Tertiary deposits and in our recent seas. 244 CHAPTER XIII. ASTEROIDEA AND OPHIUROIDEA. ORDER II. ASTEROIDEA. THE order Asteroidea or Stellerida comprises the ordinary " star-fishes," and is defined by the fact that the body (fig. 139) is star-shaped or pentagonal, and consists of a central " disc" surrounded by five or more lobes or " arms" The arms are truly prolongations of the body, are hollow, and contain pro- longations of the stomach in their interior. The arms are, further, grooved on their under surface for the reception of the ambulacral or water-vascular vessels. From these grooves the tube-feet are protruded in two or four rows. The integument (perisome} is leathery, but is more or less calcified ly the de- velopment in it of plates, granules, and spines of carbonate of lime. The mouth is inferior in position, and is toothless. An anus is usually present, but may be absent. The two most striking features which distinguish the Star- fishes from the Sea-urchins are the star-like figure of the former, and the fact that the body is not enclosed in an im- movable calcareous box or " test," as it is in the latter. The integument of the Asteroidea is, however, so richly provided with calcareous matter, that though more or less soft and flexible during life, it is quite capable of being preserved in a fossil condition. It is, of course, wholly with the cal- careous secretions of the animal that the palaeontologist has to deal ; and we may therefore dispense with any further account of the soft parts, beyond what is contained in the above definition. ASTEROIDEA. 245 In their form the Star-fishes differ considerably, though in most the figure is markedly stellate. The animal consists of a central body or " disc," which gives off radiating processes or " arms," but the size of the disc is very different in different species, and the arms vary greatly in length and in number. In many living and extinct forms the " disc " is inconspicuous, and appears to be formed simply by the junction of the bases of the arms, which in this case are normally five in number. The living Urasters and Cribellce, and the extinct Palceasters (fig. 139), may be taken as examples of this state of parts. In other forms, as in the Sun-stars (Solaster) and the extinct Lepidasters and Plumasters, the disc is very broad, exceeding or equalling the length of the arms in its diameter ; whilst the rays vary in number, from eight J J Fig. 139. Palceaster Niagarensds, or ten up to thirty or more. In Hail. Lower Silurian, the Cushion - stars (G-oniaster and Goniodiscus), again, the body is pentagonal, disc-shaped, and flattened on the two sides, and the arms can only be recog- nised by the ambulacral grooves on the lower surface (fig. 140). On the upper surface of the body, placed nearly in the centre of the disc, is the aperture of the anus, when this is present ; but the genera Astropecten, Ctenodiscus, and Luidia are destitute of a vent. Also on the upper surface is the " madreporiform tubercle," in the form of a spongy or striated disc placed at the angle of junction of two rays. It has the same function as in the Echinoids, serving to protect the entrance to the water-vascular system. Ordinarily there is a single madreporiform tubercle, but in some genera there are two, three, or more tubercles ; and there seems in some cases to be a correspondence between the number of the arms and the number of madreporic plates. Placed in the centre of the lower surface is the mouth, at the angles of which are the so-called "oral plates" (fig. 140). Eadiating from the mouth are a series of furrows, varying in 246 ASTEROIDEA AND OPHIUROIDEA. number with the arms, and termed the " ambulacral grooves." Each ambulacral groove is continued along the lower surface of one of the arms, tapering gradually towards the extremity of the latter. The floor of each groove is constituted by a double row of minute calcareous pieces the "ambulacral ossicles " which are movably articulated to one another at their inner ends. At the bottom of each groove is lodged one of the radiating canals of the water-vascular system or ambulacral system, from which are given off the rows of suctorial feet, or " tube-feet." It follows from this that the radiating vessels of the ambulacral system are outside the chain of ambulacral ossicles, so that these latter are to be regarded as an internal skel- eton, and they do not corre- spond with any part of the skeleton of Echinoids 1 at least they do not correspond with the perforated ambu- lacral plates of the Sea- urchins. The ambulacral os- sicles, however, of the' Star- fishes are of such a form that by their apposition an aper- ture or pore is formed between each pair. By means of these pores (fig. 140, a) the tube- feet communicate with a series of little bladders, or "am- pullae," placed above the chain of ossicles. These perforations, however, do not correspond with the perforated plates of the Echinoid test, and the tube-feet of the Star-fishes pass through no " poriferous " plates on their way to the exterior. This may be rendered more intelligible by examining a section of the arm of a Star-fish from which the soft parts have been removed (fig. 141). In such a section the am- bulacral ossicles (, a) are seen in the centre of the lower 1 The structures in the Echinus, which are truly homologous with the ambulacral ossicles of the Asteroidea and Opkiuroidea, are the so-called " auriculae." Fig. 140. Diagram of a Star-fish (Goniaster), showing the under surface, with the mouth and ambulacral grooves, a, Ambulacral os- sicles, with the ambulacral pores between them ; 6, Adambulacral plates, bounding the ambulacral grooves ; m, Marginal plates (wanting in many species) ; o, Oral plates, placed at the angles of the mouth. ASTEKOIDEA. 247 surface, united along the middle line by their inner ex- tremities. They are so placed as to form a kind of elongated pent-house, and immediately beneath the line where the ossicles of one side are articulated with those of the other side is placed the ambulacral vessel (5). Superficial to this, again, is a nerve-cord ; so that the whole chain of ambulacral ossicles is placed in the midst of the soft parts of the animal, and is thus clearly an internal skeleton. At their outer ex- tremities the ambulacral ossicles are articulated by the inter- vention of the " adambulacral plates" (fig. 140, &), with plates belonging to the external or integumentary skeleton, to be immediately described. As before said, the shape of the ambulacral ossicles is such that a pore is formed by the Fig. 141. Section of the ray of Uraster rubens. a, a, Ambulacral ossicles ; 5, Position of the ambulacral vessel ; c, c, Plates of the external skeleton ; n, Nerve-cord. The dotted lines show the tube-feet proceeding from the ambulacral vessel. apposition of each pair ; and by these apertures each tube- foot communicates with a vesicle placed internal to the chain of ossicles. It will be seen, however, that the tube- feet (indicated by the dotted lines in the figure) do not pass through these apertures, or through any other pores of the skeleton, on their way to the surface. The "poriferous zones " of the Sea-urchins are part of the external skeleton, and are not represented in the Star-fishes. On the other hand, the integumentary skeleton in the Star-fishes is absent along the ambulacral areas, or along the areas occupied by the ambulacral grooves. Leaving the ambulacral ossicles or internal skeleton of the Asteroidea, we come now to the integumentary skeleton. This consists of a vast number of small calcareous pieces, 248 ASTEROIDS A AND OPHIUROIDEA. or " ossicles/' united together so as to form a species of chain-armour. The ossicles are generally united with one another in a reticulated manner, and the interspaces between them are filled by the coriaceous integument. In some genera there is a single or double row of large plates round the borders of the disc and arms (fig. 140, m). These are termed the " marginal plates." The integument in the Star- fishes is also furnished with spines, tubercles, and granules of calcareous matter. The spines vary in their development and in their position in different Star-fishes ; but there is commonly a row of spines along each side of each of the ambulacral grooves. In some genera (as in Solaster, Luidia, Ctenodiscus, &c.) there are spines the summits of which carry bunches or tufts of minute calcareous processes. These are termed " paxillse." Lastly, in Asteroidea, as in Ecliinoidea, there are the modified pincer-like spines which are known by the name of " pedicellarise." As regards their distribution in time, the Asteroidea have a long vertical range, extending from the Cambrian to the present day. In the Upper Cambrian of Britain, remains of members of this order have been detected (Henry Hicks), and others have been described from rocks in Sweden, believed to be of the age of the Lower Cambrian. In the Silurian seas Star-fishes were comparatively abundant, and their re- mains are found, though rarely, in the subsequent Devonian and Carboniferous formations. In the Secondary deposits, and more especially in the Jurassic and Cretaceous, Star- fishes, often belonging to existing genera, are far from un- common ; and other types, closely related to living forms, are found in the Tertiary. As regards living forms, the order Asteroidea may be divided into the following five families : Family 1. Asteriadce or Asterocanthiidce. Four rows of ambulacral feet. Fam. 2. Astropectinidce. Two rows of ambulacral feet ; back flattish, netted with tubercles, which carry radiating spines at the tip ("paxillre"). Fam. 3. Oreastridce. Two rows of ambulacral feet; skin granular, pierced by minute pores. Fam. 4. Asterinidce. Two rows of ambulacral feet ; body discoidal or ASTEROIDEA. 249 pyramidal, sharp-edged ; skeleton of imbricate plates ; dorsal wart single, rarely double. Fam. 5. Brisingidce. Arms long and rounded, sharply marked off from the disc. Ambulacral grooves not reaching the mouth ; two rows of ambulacral feet. Owing to the imperfect state of preservation in which the remains of fossil Star-fishes are usually found, it is difficult or impossible to speak definitely as to the precise affinities of many of the extinct species. The Brisingidce are not cer- tainly known to occur as fossils, and the Asterinidce are but poorly represented ; the great majority of fossil Star-fishes being thus referable to the families of the Asteriadce, the Astropectinidce, and the Oreastridce. It should be borne in mind, however, that the singular family of the Brisingidce, forming an intermediate group between the Asteroidea and the Ophiuroidea, may possibly prove to be of very ancient origin, and to be represented by such Silurian and Devonian types as Protaster, Eugaster, Tceniaster, &c., which we may provisionally consider among the Opliiuroids. Lastly, as Star- fishes are always of rare occurrence as fossils, and as they are therefore of little importance to the general student, we shall content ourselves here with simply glancing at the more important types which have made their appearance in the successive geological periods, briefly noting some of the special characters of the more interesting ancient forms. In the Silurian period the genus Palceaster (figs. 142 and 143, B) is the most important. In this genus we have Star- fishes in which the body is five-armed, the disc being very small ; the ambulacral grooves are placed on the lower sur- face of the arms, and are furnished with two rows of ambu- lacral ossicles and pores, bordered on each side by a row of " adambulacral plates," which are, in turn, bordered by a series of " marginal plates." On the dorsal surface are three or more rows of plates, which are stated to fit closely to- gether, instead of forming pores by their junction. The genus Palceaster comprises some species of considerable size, and ranges from the Lower Silurian to the Devonian. The Silurian genus Urasterella ( = Stenaster) is in many respects like Palceaster, but the ambulacral grooves are margined by 250 ASTEROIDEA AND OPHIUROIDEA. a row of adambulacral plates only, without a second row of marginal plates. Petraster, also Silurian, has an incomplete series of disc-plates between the adambulacral and marginal rows of plates, but is otherwise almost identical with Palce- Fig. 142. Palceaster eucharis, Devonian (after Hall). A, Under side of a specimen, four of the arms being cut short ; B, Upper side of the same, a, Ambulaeral ossicles, lying in the ambulacral grooves ; &, Adambulaeral plates ; m, Marginal plates ; o, One of the oral plates ; t, Madreporiform tubercle. aster ; whilst the Silurian and Upper Cambrian Palasterina (fig. 143, A) has the disc still more extensively developed, and is further distinguished by the fact that the plates of the adambulacral series, which are placed at the angles of the Fig. 143. Silurian Star-fishes. A, Palasterina primceva, Upper Silurian ; B, Palceaster Ruth- veni, Upper Silurian ; c, Palceocoma Colvini, Upper Silurian. (After Salter.) oral aperture, are large and triangular. The genera above mentioned can hardly be grouped with any existing family of the Asteroidea, as they possess several striking peculiar- ASTEROIDEA. 251 ities of their own, more especially the presence of a row of " adambulacral plates," exceeding in size the ordinary plates of the skeleton. They might thus with propriety form a distinct family, which might be termed Palasteriadce, and which would to some extent fill up the interval between the families of the Asteriadce and Astropectinidce. Urasterella may also be best referred to the same group, especially as the plates upon the ventral surface are closely fitted together, though it wants " marginal plates," and in the characters of the upper surface presents points of resemblance to the Urasters. We are not, however, without ancient representatives of existing families of Star-fishes. Thus, the Upper Silurian Lepidaster and Trichotaster, and the Devonian Helianthaster represent the living Sun-stars (Solaster), with their wide disc Fig. 144. Under surface of Astropecten Phillipsii. of the natural size. Jurassic. (After Wright.) and numerous arms ; Devonian and Carboniferous species of the living genus Astropecten (or Asterias) have been detected, and the Upper Silurian Palceocoma of Salter (fig. 143, c) may possibly be an old form of the living " Bird's-foot Star- fishes" (Palmipes). Leaving the Palaeozoic period, the Secondary deposits are known to contain a large number of Star-fishes, which need 252 ASTEROIDEA AND OPHIUROIDEA. not detain us here, as they are almost wholly referable to living genera, though the species are distinct. In the Trias (Muschelkalk), we have the genus Pleuraster, doubtfully separable from Astropeden. In the Jurassic period we have the earliest representatives of the living genera Uraster, Solaster, Luidia, Astrogonium, arid Goniaster. The existing genus Astropeden (fig. 144), easily recognised by the great spine-bearing marginal plates, is largely represented ; while the extinct Tropidaster forms a link between this and Uras- ter ; and Plumaster, also extinct, is a near ally of the recent Luidia. In the Cretaceous rocks almost all the known forms belong to existing genera (such as Goniaster, Stellaster, Astrogonium, Palmipes, and Oreaster) ; while in the Tertiary deposits we meet only with the generic types of the present day. AGELACRINIM. We may provisionally consider here a most extraordinary group of Palaeozoic Echinoderms, the precise affinities of which are at present wholly uncertain, though they appear to be in some respects intermediate between the Asteroidea and the Cystoidea. The singular forms in question have been grouped together by Mr Billings under the name of Edrioasteridm, but are better entitled Agelacrinidce ; and they fall under the two related generic types Agelacrinus and Edrioaster. In the genus Agelacrinus or Agelacrinites (including Hemi- cystites of Hall) the body (fig. 145, A) is in the form of a depressed or convex disc, attached by its base to some foreign body. The upper surface of the disc (which is really the ventral surface) is covered with numerous small calcareous plates, which may or may not overlap in an imbricating manner, and exhibits five curved " arms," which radiate from the centre. The rows of plates forming the arms are so disposed, in some instances at any rate, as to leave between them distinct "pores," penetrating the thickness of the test; so that the arms clearly corre- AGELACRINID^:. 253 spond with the " ambulacral grooves " of the Star -fishes. The opening of the mouth appears to be placed in the centre of the five arms ; and in one of the spaces between the arms is situated a little pyramid of from five to nine calcareous plates, which forms the valvular " ovarian aper- The genus is wholly Silurian, ture" (fig. 145, A, o). Devonian, and Carbonifer- ous, and it has been gener- ally placed under the order Cystoidea. It differs, how- ever, from these in its total absence of a stalk of at- tachment, and in the pos- session of ambulacral pores, perforating the test. On the other hand, it recalls the Asteroidea in the struc- ture of the ambulacral grooves ; while the some- times articulated, some- times imbricated inter- radial ( interambulacral ) plates recall to mind the Perischoechinidce ; though we know of no parasitic or sessile examples of the Star-fishes or Sea-urchins. In the allied genus Ed- rioaster (fig. 145, B) the body is sessile, circular, discoid, and convex, and covered with irregular pol- ygonal plates. The mouth is large and somewhat pen- tagonal. Eadiating from the mouth are five ambulacral grooves, each formed of a double series of plates ("am- bulacral ossicles"), with two pores between each pair of plates. There are thus four rows of ambulacral tube-feet, as shown by the pores, which penetrate the entire thickness B Fig. 145. A, Upper surface of Agelacrinus Cin- cinnatiensis, enlarged two and a half diameters. Lower Silurian (after Hall). B, Upper surface of an imperfect specimen of Edrioaster Bigsbyi, of the natural size. Lower Silurian (after Bil- lings), o, Ovarian pyramid. 254 ASTEKOIDEA AND OPHIUROIDEA. of the test. An ovarian aperture appears to be present in one of the interradial spaces. This genus is only known as occurring in the Lower Silurian, and it is clearly very closely allied to Agelacrinus, though it has not yet been demonstrated to have been attached to foreign bodies; and its other charac- ters perhaps entitle it to generic distinction. Whether or not we may place in the vicinity of Agelacrinus the extra- ordinary Silurian genus Cydocystoides, cannot at present be stated with any certainty. Salter would also refer here the genera Echinocystites and Palceodiscus. ORDER III. OPHIUROIDEA. The Opliiuroidea are often grouped with the Asteroidea, and the living members of the order are known commonly as Brittle-stars and Sand-stars. They are distinguished from the true Star-fishes by the fact that the " disc " contains all the internal organs of the animal ; the " arms " are not grooved inferiorly for the emission of ambulacral tube -feet ; and the mouth is provided with a masticatory apparatus. The Ophiu- roids are very conspicuously star-shaped, and consist of a central "disc" and a series of radiating "arms" (fig. 146). The " disc " is truly disc-shaped, and is covered with granules, spines, or scales. From the disc proceed the arms, in the form of long and slender processes, which may be simple or branched, but which differ from the arms of Star-fishes in not containing any prolongations from the stomach, and in never having their under surfaces furrowed by ambulacral grooves. The arms, in fact, are special processes superadded for the purposes of prehension and locomotion, and rendered necessary by the fact that the ambulacral system takes no part in the function of locomotion, as it does in the Star- fishes. A madreporiform tubercle, however, is present, and is placed on the inferior surface of the body, being com- monly concealed by one of the plates surrounding the mouth. The mouth, as in the Star-fishes, is placed in the centre of the lower surface of the disc ; but the stomach terminates blindly ; and there is, therefore, no anal aperture. Each arm is furnished with an internal and an external OPHIUROIDEA. 255 skeleton. The internal skeleton consists, as in the Star- fishes, of a chain of " ambulacral ossicles," placed along the centre of the arm. The ossicles are, however, now amalga- mated in pairs, each coalescing with its fellow on the oppo- site side ; so that in place of a double row of movably articulated ossicles, we have a single row of bilaterally symmetrical pieces. Fig. 146. Under surface of Ophioderma (Ophioglypha ?) Gaveyi, of the natural size. Jurassic (Lias). (After Wright.) The external skeleton of the arms is composed of four rows of plates, one on the dorsal surface, one on the ventral, and one on each lateral surface. The lateral plates generally carry more or less developed spines. In the extinct genera Eugaster and Protaster (fig. 148) the plates of the ventral row are double; and in Ptilonaster (fig. 148) there are four ventral rows of plates. The disc, as before said, has a well - developed external skeleton of scales, granules, and 256 ASTEROIDEA AND OPHIUKOIDEA. spines ; but there are never any of those modified spines which are known as " pedicellariae," and which occur in the Asteroids and Echinoids. As regards their distribution in time, the Ophiuroids make their first appearance in the Lower Silurian, and they are represented by various ancient types in the Upper Silurian and Carboniferous. The living genus Ophiura is said to occur in the Carboniferous, but with this exception the old forms are all more or less aberrant. In the Secondary rocks, however, we meet with a large number of Ophiuroids which are referable, in large part, to familiar and widely distributed existing genera. As the Ophiuroids are, comparatively speaking, very rare as fossils, it is not necessary that we should devote much time to their consideration here. It is advisable, however, to consider with some little detail the curious Palaeozoic genera Protaster, Eugaster, and Ptilonaster, since these ex- hibit many singular and special characters, which are not to be found in the typical and more modern members of the order. These genera, in fact, are in many respects inter- mediate between the Asteroidea and Ophiuroidea ; and they might without impropriety be placed in the Asteroid family of the Brisingidce, were it not for the fact (amongst others) that the under surface of the arms is not furrowed by " ambulacral grooves." As the type of the Palaeozoic Ophiuroids in question, we may take the genus Protaster of Edward Forbes. In this genus the body (figs. 147, 148) consists of a circular disc, covered with small imbricated calcareous plates, which gives origin to five long and flexuous arms. The chief peculiarity of the genus is to be found in the structure of the arms, which show the peculiarity that they possess two rows of ventral plates, instead of one, and that these plates are opposite to one another (Salter), or very slightly alternating (Hall). These plates, moreover, are so disposed as to give origin to a series of distinct pores (fig. 148, E). If, as would appear to be the case, Tceniaster of Billings be really iden- tical with Protaster, then the genus dates from the Lower Silurian and ranges into the Devonian. In the Devonian OPHIUROIDEA. 257 genus Eugastcr (fig. 148, A and B) the structure is essentially the same as in Protaster, but the disc is prolonged along the bases of the arms, and the plates of the disc are articulated by their edges, and do not overlap. In the Devonian Ptilo- naster (fig. 148, E), again, we have a form fundamentally similar to the preceding, but having four rows of perforated plates on the lower surface of the arms. The chief question as to the affinities of the types just alluded to turns upon the true nature of the perforated plates, in double or quad- ruple series, placed along the lower surface of the arms. These have generally been regarded as identical with the " ventral plates " of the arms of the ordinary Ophiuroids structures which belong wholly to the integumentary skel- eton, and which are not represented in the As- teroids. It does not seem certain, however, that this is the true na- ture of the perforated plates of the under sur- face of the arms of the genera above alluded to; and it is not impos- sible that they are really the internal " ambula- cral ossicles " of the arms, exposed to view by the destruction Of tVip cmnprfipinl " vpntral Ventral plates " during fossilisa- tion. Should this turn out to be the case, the structure of Protaster and its allies is not so abnormal. If, on the other hand, these perforated plates are really the " ventral plates," then these genera exhibit the peculiarity that the under sur- faces of the arms are pierced by " ambulacral pores." The only other Palaeozoic type which needs notice here is VOL. I. R Fig. U7.- Protaster SedgwictH. Upper Silurian. A> Disc and bases of the anns ' ma 8 nified '> B > of an arm g^^ enlarged. 258 ASTEKOIDEA AND OPHIUROIDEA. Eucladia, described by Dr Henry Woodward from the Upper Silurian, which apparently belongs to the section of the Opliiuroids represented at the present day by Euryale, in which the arms, instead of being simple, are bifurcated. Fig. 148. A, Outline of Eugaster Logani, of the natural size Devonian. B, Base of an arm of the same viewed from below, enlarged, c, Outline of Protaster Forbesi, of the natural size Upper Silurian. D, Base of arm of same, viewed from below, enlarged. E, Portion of the arm of Ptilonaster princeps, viewed from below, enlarged Devonian : a, Ambulacral plates ; 6, Adambulacral plates ; p, Pore. (After Hall.) As regards the Secondary and Tertiary Ophiuroids very little need be said, partly because they approximate closely to, or are identical with, recent generic types, or because they are so imperfectly preserved, as a rule, that their determina- Fig. 149. Aspidura loricata. Muschelkalk. tion is exceptionally difficult. In the Trias appear the genera Acroura and Aspidura (fig. 149), the latter being OPHIUROIDEA. 259 supposed to be confined to this period and to be character- istic of the Muschelkalk. In the Jurassic and Cretaceous periods, as in the Tertiary, remains of Ophiuroids are by no means very uncommon, and they are generally referred partly to extinct types (such as Acroura). Most of them, however, are apparently referable to well-known existing genera, such as Ophioderma (fig. 146), Ophiocoma ( = Ophi- urella), OpMoylyplia (- Ophiura, Forbes), Ophiolepis, and Amphiura. 260 CHAPTER XIV. ORDER IV. CRINOIDEA. THE Crinoids or Sea-lilies are Echinodermata, in which the body is fixed, during the whole or a portion of the existence of the animal, to the sea-bottom by means of a longer or shorter, jointed, and flexible stalk. The body is distinct, composed of articulated calcareous plates, bursiform, or cup-shaped, and provided with branched arms, which are typically from five to ten in number, are independent of the visceral cavity, and are grooved on their upper surfaces. (The position of the body being reversed, the upper surface is ventral ; whilst the dorsal surface is inferior, and gives origin to the pedicle.) The tubular processes, however, which are given off from the radiating ambulacral canals of the Crin- oidea, unlike those of the Echinoidea and Asteroidea, are not used in locomotion, but have probably a respiratory function. The mouth is central, and looks upwards, an anal aperture being sometimes present, sometimes absent. The ovaries are situated beneath the skin in the grooves on the ventral sur- faces of the arms or pinnules, as are also the ambulacral or respiratory tubes. The arms are furnished with numerous lateral branches or " pinnulse." The embryo is " free and ciliated, and develops within itself a second larval form, which becomes fixed by a peduncle " (Huxley). If we take such a living Crinoid as Rhizocrinus (fig. 150), we shall be able to arrive at a comprehension of the leading characters of this order. Rhizocrinus is one of those Crinoids CRINOIDEA. 261 which is permanently rooted to some foreign object by the base of a stalk which is composed of a number of calcareous pieces or articulations. In some cases (as in Apiocrinus) the base of the stem or " column " is considerably expanded. In other cases the column is simply "rooted by a whorl of terminal cirri in soft mud" (Wyville Thomson). The joints of the column are movably articulated to one another, the joint -sur- faces often having a very elaborate structure, so that the entire stem possesses in the living state a greater or lesser amount of flexi- bility. Each joint is per- forated centrally by a canal, which has been very inap- propriately termed the " ali- mentary canal," but which in truth has nothing to do with the digestive system of the animal. At the summit of the stem is placed the body, which is termed the " calyx," and which is usually more or less cup - shaped, pyriform, bursiform, or dis- coidal. The calyx exhibits two surfaces, a dorsal and a ventral, of which the dorsal is composed, wholly or in part, of calcareous plates articulated by their margins, whilst the former is, in the living forms, composed of a more or less leathery integument, strengthened by the deposition in it of numerous small plates of carbonate of lime ; whereas in many extinct forms it too is composed of articulated cal- Fig. 150. Crinoidea. Rhizocrinvs Lofo- tensis, a living Crinoid (after Wyville Thom- son), four times the natural size, a, Stem ; b, Calyx ; c, c, Arms. 262 CRINOIDEA. careous plates. The ventral surface exhibits the aperture of the mouth, which may be subcentral or may be very excen- tric, and which in many extinct forms is wholly concealed from view. The ventral surface also exhibits the aperture of the anus, which is usually placed excentrically in one of the spaces between the arms, and which is often carried at the end of a longer or shorter tubular eminence or process, which is called the " proboscis. " Sometimes, on the other hand, the anus is central, and the mouth is excentric. wing- to the animal being supported on a stalk, it is evident that the " ventral " surface is turned upwards, and the " dorsal " surface downwards. The column springs from the centre of the dorsal surface ; and a stalked Crinoid may therefore be compared to a Star-fish turned upside down, with its lower or ambulacral surface superior, and its dorsal surface looking downwards. The calyx contains the digestive canal, and the central portions of the nervous and water-vascular (am- bulacral) systems ; but it does not contain the reproductive organs, as is the case with the visceral cavity of the other Echinoderms. From the margins of the calyx, where the dorsal and ventral surfaces join one another, arises a series of longer or shorter flexible processes, which are composed of a great number of small calcareous articu- lations, and which are termed the " arms " (fig. 151). The arms are usually primarily five in number, but they generally divide almost immediately into two branches, each of which may again subdivide ; the branches thus produced perhaps again dividing, until a crown of delicate graceful filaments is formed. The arms carry smaller lateral branches or " pinnulse " on both sides ; and they are not hollow like the arms of the showing the lateral pin- Star-fishes, nor do they contain any pro- nulae. The lon^ations of the stomach. upper surface of the arms and pinnulae is covered with a soft mem- brane, and below this are placed the reproductive organs. CR1NOIDEA. 263 The generative organs are therefore not placed within the calyx, and it follows of necessity that there is no generative opening or " ovarian aperture " in the walls of the calyx. The ventral surfaces of the arms and pinnulse are furnished with grooves, which in the living species are seen to be covered with vibratile cilia. The brachial grooves coalesce till they constitute five (sometimes fewer) primary grooves, which are continued from the bases of the arms to the mouth. The action of the cilia gives rise to a constant current of sea- water, bearing organic matter in suspension; and this current proceeds from the brachial grooves to the mouth. In this way the animal obtains its food. As the bases of the arms are separated from the mouth by an intervening space, it follows that the brachial grooves are continued over the ventral surface of the calyx, till they reach the oral opening. Fix. 152. Platycri-nus tricontadactylus. Carboniferous. The left-hand figure shows the f-alyx, arms, and upper part of the stem, and the figure next this shows the surface of one of the joints of the column. The right-hand figure shows the proboscis. There is no doubt that it is by the above arrangement that the living Crinoids obtain their food, and the mechanism seems to have been essentially the same in many extinct species. In the Palaeozoic Crinoids,, however, there seems to 264 CRINOIDEA. have been a modification of this arrangement. In these forms, as in Actinocrinus (fig. 153), the arms have much the structure of those of the recent Crinoids, and are deeply grooved on their ventral surfaces. The ventral surface of the calyx, however, exhibits no central aperture, but only a proboscidiform tube, which arises from one of the inter-radial spaces (i.e., one of the intervals between two of the arms). This tube is often of great length, and a good deal of con- troversy has taken place as to its nature. Without entering into the conflicting views upon this subject, it may be stated that the preponderance of authority is overwhelmingly in favour of the view that this " proboscis " is an anal tube, Fig 153. Calyx of A ctinocrinus ro- tundus. Fig. 154. Calyx of Actinocrinus Ko- nincki. Fig. 155. Calyx of A. Verneuillanus. The arms are wanting, and the aper- tures at their bases are seen. having the vent at its extremity, all analogies based upon recent forms bearing out this view. In the ancient types in question, at any rate, the grooves on the ventral surfaces of the arms are certainly not continued over the ventral surface of the calyx, but, on the contrary, stop short at the bases of the arms. Their further course was long a mystery ; but it is now known that they are continued 'below the ven- tral surface of the calyx as a series of covered passages or tunnels, the external apertures of which are placed at the points where the arms spring from the disc (see figs. 153- 155). These covered channels are simply roofed over by the calcareous integument of the calyx ; and they converge to a central point in the middle of the ventral surface of the disc. Here is placed the mouth, concealed by the calcareous plates of the perisome. In this point of their structure, CRINOIDEA. 265 therefore, there is an extremely important distinction be- tween the older types of Crinoids and the later ones, though the process by which the microscopic organisms which serve as food are collected from the surrounding water and con- veyed to the mouth, seems to have been in both cases essen- tially the same. Moreover, even in the living Antedon, as shown by Dr Carpenter, the true mouth is situated at a little distance below the apparent mouth, as formed by the point of convergence of the brachial furrows ; so that if we imagine these furrows to be roofed over by calcareous plates, where they cross the ventral surface of the disc, we should have a condition of parts closely resembling what we find in the Palgeocrinoids. The stalked or " pedunculate " Crinoids of the present day are few in number, and are mostly inhabitants of the deep sea. We find, however, various and widely distributed rep- resentatives of another group of Crinoids namely, the " sessile " Crinoids, all of which are generally known as " Feather-stars." In all these, such as the living Comatula, Antedon, Actinometra, &c., and the extinct Saccosoma (fig. 156) and Solanocrinus, the animal is only stalked when young, and in its adult condition leads a free life. The young form in the members of this group is supported upon a jointed calcareous column, by which it is fixed to some foreign object ; and at this stage it in no respect differs from the ordinary stalked Crinoids. At a certain period of its existence, however, the calyx drops oif its column, and becomes a locomotive animal. It now has a near resem- blance to one of the Brittle-stars (Opkiuroidea) ; but is dis- tinguished, not only by its developmental history, but also by its internal and skeletal structure, by the possession of lateral pinnae to the arms, and in having the reproductive organs situated external to the body proper. In the Feather- stars, moreover, the dorsal surface of the disc, at the point where the column was originally inserted, carries a series of jointed filaments or " cirri," by which the animal can moor itself to any foreign object. These may be regarded as homologous with the " side-arms " of the column of certain Crinoids. When the animal is thus temporarily moored 266 CRINOIDEA. by its dorsal cirri, it is placed in the ordinary position held by the Crinoids namely, with the mouth and ven- tral surface of the disc looking upwards. When creeping about, on the other hand, by means of the long and flex- Fig. 156. Saccosoma pectinata, a free Crinoid. Jurassic. ible arms, the animal occupies the position held by the Star-fishes and Ophiuroids namely, with the mouth and ventral surface of the disc directed downwards, or towards the ground. Having now given a general account of the structure of the Crinoids, it remains to consider some of their parts in CRINOIDEA. 26*7 greater detail. In the first place, as regards the " column," we find that the stem of attachment is composed of a great number of separate plates or " articulations " placed one above the other, and so jointed to one another that whilst Fig. 157. Pentacrinus fasciculosus, showing the form of the column, and one of the facets of a joint. The central figure shows the arms, and the summit of the column with side-amis. the amount of movement between any two pieces must be very limited, the entire column acquires more or less flexi- bility. In the Palaeozoic Crinoids, with few exceptions, the 268 CRINOIDEA. column was round ; but in Platycrinus it is oval or elliptical (fig. 152). In the genera Pentacrinus (fig. 157) and Extra- crinus the column is pentagonal in outline ; but much less markedly so in the former than in the latter genus. The joints articulate with one another by surfaces or facets which are differently marked in different cases. In the Palaeozoic forms, as in Platycrinus (fig. 152), the articulating facets are marked by more or less numerous striae which radiate from near the centre of the joint. In most of the Mesozoic genera, on the other hand, as in Pentacrinus (fig. 157), the articu- lating facets are united by crenated ridges arranged in a pentapetalous figure. In many cases, as in Extracrinus and Pentacrinus, the column is furnished with more or less numerous " auxiliary " arms, or " side-arms," the function of which is not altogether clear. The column increases in height by the interpolation of new joints between the base of the calyx and the highest articulation of the stem ; and each ar- ticulation is pierced by a variously shaped perforation. Hence, by the apposition of the successive joints there is formed a tube the so-called " alimentary canal " of the older writers which runs the entire length of the column. This canal is most commonly round, but it may be pentapetalous, or it may consist of four or five canals running parallel with and around a central tube, into which they may or may not open. This canal sends off diverticula into the side-arms and the root-like processes of attachment, when these struc- tures are present ; and it contains, in living forms, a vascular axis (partly nervous in nature ?) which is connected superiorly with a peculiar chambered organ situated in the base of the calyx, and which doubtless serves to maintain the vitality of the column and its appendages. The dorsal surface of the cup or " calyx " is composed of a number of calcareous plates accurately fitted together. The number and arrangement of these vary much in different genera, and it will be sufficient to indicate here their gen- eral disposition. 1 Eeposing directly upon the summit of the 1 Different authorities have employed the various terms connected with the plates in the calyx of the Crinoidea in such different senses that the subject of the anatomy of the Crinoidal skeleton has been rendered very difficult to CRINOIDEA. 269 column is a series of plates which are termed " basal " from their position, and which constitute the " pelvis " of Miller. The " basal s " may be five, four, three, or rarely two in num- ber, and they form the lowest portion of the cup. In general the basals are free, and are simply articulated by their edges, but in some cases it is believed that they are more or less undistinguishably fused with one another into a single mass. In many cases the " basals " are succeeded by a Fig. 158. Diagram to show the structure of the calyx in the fossil Crinoicls. b, Basals ; r, Uadials ; i. Inter-radial s ; a, Anal plates. Calyx of Forbesiocrinus. After De Koninck and Le Hon. (As it has now been discovered that this genus really possesses three small basals, below the plates here represented, the pieces lettered b are truly "parabasals.") second row or cycle of plates, which may be regarded, with Professor Beyrich, as a second series of basals, but which are properly regarded as something special, and are termed the "parabasals" or " sub-radial s." The basals (fig. 158, b) are comprehend. To this cause of confusion must be added the fact that different observers have employed the same terms for parts which do not appear to be truly homologous. In the present state of uncertainty upon the whole of this subject, it has seemed sufficient to give here merely a general account of the nomenclature which has hitherto been most generally employed in works descriptive of the fossil Crinoids, though this nomenclature is probably often not strictly correct. 270 CRINOIDEA. in other cases succeeded directly by a series of two or three rows of plates, which are directly superimposed upon one another, and which form the foundations of the arms (r, r). These are termed the " radials " (the " costse " of Miller), and are termed " primary," " secondary," and " tertiary," accord- ing to their distance from the basals. The last radial plates, or those furthest from the column (sometimes called the " axillary radials "), give origin to the arms. The radial plates are arranged in a series of vertical columns, which ex- tend from the summit of the basals to the bases of the arms. Between the different columns of radial plates, however, there may be intercalated certain other smaller plates, which alternate with one another, and which are termed " inter- radials " (i). Lastly, one of the inter-radial spaces, corre- sponding with the anus, is usually much wider than the others, and is furnished with an additional series of plates, which are called the " anal plates " (a). As regards their general distribution in time, the Crinoidea present us with an excellent example of a group which early attained its maximum of development, and which has now dwindled down to some half-dozen surviving genera. With one or two doubtful exceptions, the Crinoids appear, so far as yet known, to have commenced their existence in the Lower Silurian period, and they are represented by numerous and very varied forms in the seas of the Upper Silurian period. In the Devonian rocks, also, Crinoids are plentiful, and many generic types are peculiar to this period. It is in the earlier portion, however, of the Carboniferous period that the Crinoids attain their highest development. The Car- boniferous Limestone is in many places, over wide areas, and for a thickness of many yards, almost entirely made up of the debris of Crinoids ; and in many places it is so charged with the remains of these organisms as to deserve and acquire the name of " crinoidal limestone " or " entrochal marble." It is in the Palaeozoic period, then, that the Crinoids attain their maximum, both numerically and as regards the number of genera and species. Taken as a whole, the Palaeozoic Crinoids are distinguished by the characters already men- tioned namely, by having the brachial grooves conveyed to CRINOIDEA. 271 the mouth in concealed channels or tunnels, in having mostly a rounded column, and in the fact that the articular facets of the column-joints are usually marked by numerous simple radiating striae. As a rule, also, the Palseocrinoids have a calyx, in which the dorsal surface has a preponderating development as compared with the ventral surface. Coming to Mesozoic times, Crinoids are still abundant, though certainly reduced in numbers as compared with their development in the Palaeozoic period. Taken as a whole, the Mesozoic Crinoids are characterised by having the brachial grooves continued over the ventral surface of the disc, and by having the ventral portion of the calyx more extensively developed than the dorsal ; whilst the articular surfaces of the column-joints are usually morticed to one another by means of crenated ridges which have a flower-like arrange- ment. Neither of these latter characters, however, is con- stant. In the Mesozoic rocks, also, appear for the first time remains of the free Crinoids allied to the living Comatulce. In the Tertiary period the Crinoids are reduced to a very small number of forms, the most important of which is the genus Pentacrinus, which is represented at the present day by the living Pentacrinus caput-Medusce of the Antilles and various other species. The best-known species is the P. sub- lasaltiformis of the Eocene. At the present day, Crinoids are moderately abundant, if we look only to the free forms like Comatula, which are largely represented, and attain their maximum in recent seas. On the other hand, the stalked Crinoids are reduced to a comparatively very limited number of generic types represented by a comparatively small number of species. A good classification of the Crinoids is still a desideratum. Commonly they have been divided into two groups termed respectively Articulata and Tesselata, according as the radial plates of the calyx are freely articulated to one another, or are immovably joined together without articulation. This arrangement is a far from satisfactory one ; but if accepted, we should have all the Mesozoic and Kainozoic Crinoids (except Marsupites) in the division of the Crinoidea arti- culata. On the other hand, the division of the Crinoidea 272 CBINOIDEA. tesselata would correspond with the Palaeocrinoids, compris- ing all the species known from the Palaeozoic formations. The division of the Crinoidea into stalked and free forms is in many respects inapplicable as a basis of zoological classification. There can, however, be no doubt but that the free Crinoids are structurally an advance upon the fixed forms. It is therefore of interest to note that the stalked Crinoids had attained their maximum in the Palaeozoic rocks, and had even commenced to decline before the free Crinoids first made their appearance in the Mesozoic Series. In the absence of any satisfactory classification of the Crinoids, it will be sufficient here to briefly consider the Fig. 159. A, Diagram, showing the dissected calyx of CyatJwcrinus (after Hall), ft, Basals ; p, Parabasals ; r, Lowest of the three radials (" primary radials ") ; a, Anal plate. B, Calyx and part of the arms of Cyathocrimis planus, of the natural size. Carboniferous. leading types and geological range of the more important families of the order. It should be borne in mind, however, that though some of these families are undoubtedly natural assemblages, the same cannot be affirmed of all of them, while there often exist considerable and legitimate doubts as to the true position of many of the genera. The family of the Cyathocrinidce, as represented by Cyath- ocrinus itself, presents us with one of the simplest types of the Pedunculate Crinoids. In Cyatliocrinus (fig. 159) the CRINOIDEA. 273 calyx is somewhat globular, consisting of five " basals," alter- nating with an equal number of "parabasals" or "sub- radials," these in turn being followed by the " radials." There are generally three " radials " to each arm, the primary radials being comparatively large, while the other ones are small. There are no " inter-radials." The structure of the upper surface of the calyx in this genus has not yet been completely made out. The vault of the calyx is always slightly arched, or comparatively flat and depressed, and there appears to be a small anal proboscis on one side. A central mouth has been described as present ; but specimens examined by Meek and Worthen would go to show that the ap- parent mouth is due to breakage, and that the summit of the calyx is really vaulted over by calcare- ous plates, the mouth, as in the Palseocrinoids generally, being thus hidden from view. The genus CyatJiocrinus is mainly confined to the Carboniferous and Permian rocks, though examples have been described from both the Silurian and Devonian. The Carboniferous genus Zeacrinus is also related to CyatJiocrinus, but the basals are very small, and there are four, six, 01- more anal plates. We may place here also the curious Icktliyo- crinus of the Silurian and Car- boniferous (fig. 162, &), the arms of which are frequently bifurcated. Allied to the preceding is the Fig. 160. Calyx and part of the family Of the PoteriOCmnidce, Of arms of Poteriocrinus radiatus, show- -, . -, T-, , . . ,, ing the proboscis. Carboniferous. Which PoteriOCnnUS IS the type. (After De Koninck and Le Hon.) In this genus (fig. 160) the cup consists, as in CyatJwcrinus, of five basals, five parabasals, and a variable number of radials, the primary radials being the largest ; and there are no inter-radials. There are, VOL. I. s 2*74 CR1NOIDEA. however, four to six anal plates ; and the upper surface of the calyx, instead of being depressed, is always swollen and convex, and furnished with a very large anal tube or " pro- boscis." The genus (with various sub-genera) commences in the Silurian, is present in the Devonian, and abounds in the Carboniferous period, after which it disappears. If the Car- boniferous genus Zeacrinus be proved to have a large pro- boscis, it will have to be removed from the Cyathocrinidce and placed here. The Silurian genus Dendrocrinus also stands very close to Poteriocrinus, and possesses a greatly- developed proboscis, in some species of extraordinary length. In the little group of the Rhodocrinidce, typified by the Carboniferous genus Rliodocrinus (fig. 161) there are five basals Fig. 161. Diagram of the dissected calyx of Rhodocriints (after Schultze). b, Basals ; p, Parabasals ; r, First radials ; i, Inter-radials ; a, Anal plates. and five parabasa]s or sub-radials ; there are three cycles of radial plates ; there are from six to eight " inter-radials " in each inter-radial space ; the anal plates are eight to twelve in number ; and the arms, varying in number from ten to twenty, are bifurcated two or three times during their course. Very nearly allied to likodocrinus, though apparently separ- able from it, is the Carboniferous genus Gilbcrtsocrimis. CRINOIDEA. 275 All the preceding families are provided with a zone of " parabasal " or " sub-radial " plates, and if we regard this character as being of high classificatory value, we must con- sider here the groups of the Taxocrinidce and Anthocrinidce, both of which in some respects differ widely from the typical Palasocrinoids. In the Taxocrinidce, typified by the genus Taxocrinus (fig. 162, c) of the Silurian, Devonian, and Carbon- Fig. 162. Upper Silurian Cfinoids. a, Calyx and arms of Eucalyptocrinus polydactylus, Wenlock Limestone; b, Ichthyocrimis Icevis, Niagara Limestone, America; c, Taxocrinus tuberculatus, Wenlock Limestone. (After M'Coy and Hall.) iferous deposits, there are three very small basals, succeeded by five large sub-radial or parabasal pieces, which support from three to seven cycles of radials. The inter-radials may be wanting, and are always few in number. The discovery that Forbesiocrinus, of the Devonian and Carboniferous, really possesses three minute basals (not represented in fig. 158, after De Koninck and Le Hon, in which the plates lettered b thus really are the " parabasals "), places this genus in the immediate neighbourhood of Taxocrinus, from which it is only separated by the possession of numerous inter-radial and anal plates. Taxocrinus is remarkable, as compared with almost all the Palseocrinoids, in apparently having the upper surface of the calyx covered by soft integument only, ^instead of being vaulted over with calcareous plates. 276 CPJNOIDEA. In the family of the AntJwcrinidce we have only the extra- ordinary Silurian genera which have been described as AntJio- crinus and Crotcdocrinus. In the former of these (fig. 163), Fig. 163. A, Calyx and arms of Anthocrinus Loveni, cut across to show how the arms arc rolled up ; B, A portion of the network formed by the arms, enlarged. Upper Silurian. (After J. MUller.) which is the best known, the calyx consists of five basals, five parabasals, and a single zone of radials, while inter- radials are wanting, and there is only one anal plate. The arms are bifurcated, and the subdivisions unite with one another by means of lateral processes, thus giving rise to a network, perforated by numerous apertures (fig. 163, B). The five flattened or leaf-like expansions, produced by this curious metamorphosis of the arms, are rolled up like the petals of a flower. Crotalocrinus in the conformation of its arms appears to resemble Anthocrinus, except that the edges of the arms appear to be united, but the structure of the calyx is somewhat different. Fig. 164. Haplocrimis mespiliformis. The calyx viewed from below, from one side, and from above. Devonian. Lastly, we must place here the little family of the Haplo- crinidce. In the Devonian genus Haplocrinus (fig. 164) the calyx is small and globular, with five small basals, sue- CBINOIDEA. 277 ceeded by a cycle of three parabasals. There are five radials, two of which stand directly upon the basals, while the others rest on the parabasals. The upper surface is covered by five inter-radials, so disposed as to form a pyramid. In the related genus Trwcrinus, of the Silurian and Devonian, there are only three basals, and a single parabasal. We come now to a series of the stalked Crinoids in which there are no parabasal plates. Foremost among these is the great family of the Actinocrinidce, of which Actinocrinus itself is the type. In this genus the calyx (figs. 153-155), though very variable in shape, consists of three basals (fig. 165, b), which articulate upwards with three cycles of radials, the " sub-radials " being wanting. The axillary radials carry each a double series of brachial plates, which support the vari- ously divided arms. There are three or more' anal plates, of which the lowest (fig. 165, a) always rests upon the basals directly. There is a variable number of inter-radials, and the column is round. The upper surface of the cup is vaulted over with calcare- ous plates, and the brachial grooves are continued be- neath the vault thus formed, as so many tunnels, to the central and concealed mouth. The anus may or may not be extended into a proboscis, and it is sometimes very excentric, sometimes sub- central. It has been shown that in many of the Actin- ocrinidce there exists in the interior Of the Calyx a Sin- Fig . i65.-Diagram of the dissected calyx of gular Convoluted CalcareOUS ^