LECTURES ON MOLLUSCA; OR SHELL-FISH" AND THEIE ALLIES. PREPARED FOR THE SMITHSONIAN INSTITUTION, BY PHILIP P. CARPENTER, B. A., PH. D., OP WARRINGTON, ENGLAND. WASHINGTON: PRINTED AT THE CONCESSIONAL GLOBE OFFICE. 18G1. , n i* i i ' ;"'i ~~ M ALLUi Gift of C. A. KofoW EARTH SCIENCES LIBRARY LECTURES ON MOLLUSOA; OR "SHELL-FISH" AND THEIR ALLIES. PREPARED FOR THE SMITHSONIAN INSTITUTION, BY PHILIP P. CARPENTER, B. A., Ph.D., OP WARRINGTON, ENGLAND. Who has not admired the beauty of shells? the rich luster of the Cowries; the glossy polish of the Olives; the "brilliant painting of the Cones ; the varied layers of the Cameos; the exquisite nacre of Mother- of-pearl? Who has not listened to the mysterious " sound of the, sea" in the Whelks and Helmets, or wondered at the many chamhers of the Nautilus? What child ever went to the sea shore without picking up shells; or what lady ever spurned them as ornaments of her parlor? Shells are at once the attraction of the untutored savage, the delight of the refined artist, the wonder of the philosophic zoologist, and the most valued treasures of the geologist. They adorn the sands of sea- girt isles and continents now; and they form the earliest " footprints of the sands of time" in the history of our glohe. The. astronomer, wandering through boundless space with the grandest researches of his intellect, and the most subtle workings of his analysis, may imagine, indeed, the history of past time and speculate on the formation of globes ; but his science presents us with no records of the past. But the geologist, after watching the ebb of the ocean tide, examines into the soil on the surface of the earth and finds in it a book of chronicles, the letters of which are not unknown hieroglyphics, but familiar shells. He writes the history of each species, antedating by millions of years the first appearance of man upon this planet, the abrasion of the Mis- sissippi Valley, or the roar of the Niagara at Queenston Heights. He searches deeper and deeper into the rocky crust of the globe, still find- ing the same types in older characters. As he climbs the rocks of Trenton or Montmorenci, rne treads on the tide-ripples, the rain drops, the trails of living creatures in the ancient Silurian sea, which he in- terprets by the Rosetta Stone of Chelsea Beach or Charleston Harbor ; and as he reverently unlocks the dark recesses which contain the tradi- tions of the early ages, between the dead igneous rocks and the oceanic deposits which entomb the remains of life, the first objects which meet his gaze are the remains of a thin, horny shell, so like those now living in the Atlantic and Pacific waters, that the "footprint" enables him to reconstruct a Brachiopod with delicate ciliated arms and com- M334382 1 LECTURES ON MOLLUSCA. plex organization , such as is figured in the beautiful works of Owen and Davidson, from dissections of the existing species. For be it observed that shells are not things without life, as they are often taken to be by thoughtless admirers. Nor are they simply the habitations of "shell fish," as ordinary observers consider them. It is common to regard the snail-shell as the house which the creature has made and carries on its back, having a relation to the animal inhabit- ant analagous to that of the coccoon to the chrysalis or the nest to the bird. Even viewed in this light, shells would be most interesting ob- jects of study; representing the different styles of architecture invented by these insignificant mechanics. Such appears to have been the way in which the great Linnasus regarded them ; for he described the ani- mals under other names than those of the shells. Indeed,, he appears to have considered the houses of far more importance than their inhab- itants; for, while he divided the shells into genera and species, he was content to group all the living inhabitants under five names, saying in the description of each genus "Animal a Clio," &c.* Even in his error, however, the great Father of Natural History showed his close discernment; for these five divisions correspond almost exactly to the classes afterwards prepared by Cuvier, and now generally adopted. Let it be distinctly understood, therefore, at the outset, that shells are truly organic structures, part and parcel of the living animal, as truly as the nails of man, the plumage of birds, the armor of arma- dilloes and crocodiles, the scales and cartilage of fishes, or the shell of the sea urchin. They are more truly part of the living inhabitant than the skin of caterpillars or the shell of crabs, inasmuch as they are not periodically cast off, but remain, as the hardened skin of the creature, during its whole period of existence. To collect and arrange shells, therefore, bears the same relation to science as to collect and arrange stuffed birds and beasts; in either case we know only a part of the peculiarities of the animal. The mere museum-student would not know the porpoise to be a mammal ; nor discriminate the manatee as being an abnormal pachyderm ; nor observe the wide separation be- tween the horse and the hoofed ruminants. So the mere conchologist would associate the Wendletrap with the top-shells, the nerites with the Naticas, the Cerithiums with the whelks, &c., not knowing that the animals are structurally as much unlike as the mammals just mentioned. It is absurd, therefore, to study shells without examina- tion of the soft parts of the animals; while, to study the soft parts alone, without regard to the differences in the shells, would be like endeavoring to classify the cat-tribe from examination of tigers, pan- thers, &c., which had been previously skinned. No one despises a collection of stuffed birds because so few of the creatures have been dissected ; so we ought not to despise the study of shells because we know so little of their inhabitants. But the bird skin tells us much more about the bird than does the shell about the "shell-fish;" because the shell is the hardened skin only of 'a portion *The Linnaean Molluscs are Sepia, Limax, Clio, Jlnomia, and rfscidia. The animal ot Terebratula was not then known. LECTURES ON MOLLUSCA. 5 of the animal, (called the mantle,) the head and foot, and other im- portant members, not leaving any impress on their unpliant covering. It is only of late years that enquirers have even attempted to gain information about the animals of shells. The very beauty of the shell has contributed to this result. Every sailor could collect shells, and every lady could lay them on cotton in a drawer; the animal was a nuisance, liable to rot if not carefully extracted, only to be preserved in bottles of spirit, and then presenting nothing but a shriveled or shapeless mass, fit only for the dissector's knife. Even the figures of living animals in the works of scientific voyagers are by no means in- fallible, it being not uncommon to find voracious proboscids figured with a vegetarian snout, or to see the shell turned the wrong way on the back of the crawler. When it is remembered that a large pro- portion of "shell-fish" live in deep water; that even those which surround our coasts can be but seldom examined in their natural con- dition ; that very few will breed in confinement, and that travelers are very seldom able to dissect and examine microscopically, or even to draw correctly while on their expeditions; we must be content to wait many years before this branch of natural history is as satisfactorily established as other branches of popular science. Let not this, however, deter any one from its pursuit. If we only collect, arrange, and study shells, we are doing something. We at least prepare a store of materials for future use. And every one can examine alive and report upon the shells of his own locality, whether land, fresh water, or marine. There is not a schoolboy, or a western farmer, but what may be not merely a learner of what others have done, but a gainer and teacher of fresh knowledge : while to those who can engage in scientific travel, there is open a field of original research, such as but few branches of science have left untrodden. At the present moment, we cannot agree upon the main divisions of our classification of shell-fish, for want of knowledge of the animals, habits and food of some of the commonest shells, which are annually collected by the hun- dred or the thousand merely for the purposes of trade. In old days, when every one followed Linnaeus, it was easy to count whether a shell had one, two, or many valves, and name it, with con- fidence that its place would not have to be disturbed. In the second epoch of study, after Cuvier had introduced an approximation to a natural system, all the world laid aside the artificial method, and arranged their books and shells according to the system of Lamarck. But now that we are as much in advance of Lamarck as he was of Linna3us ; and every fresh animal that is examined may alter our clas- sification ; we must be content to alter and amend our books with every succeeding edition, and not allow ourselves to consider anything as fixed. The arrangement proposed in these pages may serve as an approximation to the truth, or as a starting point to begin from ; neither ignoring recent discoveries, nor departing from recognized facts without better authority than hasty observations. Another difficulty is much more serious. Most of the early natu- ralists, and many in our own day, have been in the habit of naming shells without describing them ; or have described them so loosely that it is a matter of opinion only what they meant by their words ; or have 6 LECTURES ON MOLLUSCA. taken no steps to make their works known in other countries. In real, and even necessary, ignorance of their labors, or in despair of under- standing them, or purposely ignoring the existence of what was care- lessly done, the same shells have been named over and over again, thereby burdening the memory and confusing the young student with a mass of unnecessary, meaningless, or even barbarous terms. Even this evil could be borne ; for the synonymy could be made out, and henceforth all but the right name disregarded ; if naturalists were agreed as to the right principles of selection. The absolute law of priority is followed by some as the most convenient. Others think that to discard names universally accepted, merely because some ob- scure amateur published a tract a few years earlier, or some Curator of a museum wrote his fancy names on the specimens a year in advance, or an auctioneer named his wares to effect a sale, is to strain a prin- ciple contrary to the law of use. The British Association for the advancement of Science issued a series of regulations which were gen- erally approved, and which were republished by the American Asso- ciation. But Science is a republic in which the minority refuses to be ruled by the majority ; and it so happens that the newest authors have set the Scientific Associations at defiance. Those who have no access to books naturally follow the newest authorities, especially when these have deserved well of science by their discoveries. Hence we must hold our names in abeyance, and wait till better times ; taking care at any rate not to add to the confusion. The limitations of the law of priority laid down by the British and American Associations appear however to be sound. A naturalist ought not to want his own name to appear, even though the first given, if the wide use of another makes it more convenient for science. Personal considerations ought always to give way to utility : because the knowledge is the end ; the helpers to the acquisition of that knowledge are only means to that end. And what of honor the Christian naturalist would not claim for himself, against the uses of science, he is not bound, for the mere semblance of justice, to reserve for others. According to the laws of all civilized nations, possession of property for a given term of years confers legal right. A similar statute of limitations for scientific nomenclature would save a vast amount of time from being frittered away on merely archaeological research, or worse than empty recrimination. Those who are not deterred by the above statement of difficulties from the study of shells are recommended to possess themselves of the following works : "Woodward's Manual of the Mollusca : London, John Weale." "Philippi's Handbuch der Conchyliologie und Mala- cozoologie. Halle, 1853." " G-enera of Recent Mollusca by H. & A. Adams: London, Van Voorst." Dr. J. E. Gray's " Guide to the Sys- tematic Distribution of Mollusca in the British Museum, London." Chenu's " Manuel de Conchyliologie et de Paleontologie Conchyliol- ogique : Paris." These are all cheap books. Woodward's contains by far the greatest amount of information in the smallest compass, and is well illustrated. The work of Philippi has no plates, nor has that of Gray. The Adams' figure the animals when known ; but, with Gray, disregard the British Association rules, and upset the familiar Lamarckian names. Chenu's work (which, with Gray's, is still un- LECTURES ON MOLLUSCA. 7 finished) is for the most part a reproduction of Adams' G-enera with the addition of fossils ; and is chiefly valuable for its copious and accu- rate figures of shells illustrating the subgenera. The following pages are intended simply as an introduction to any of the above works. Books of older date are necessarily so full of errors that they should not be studied till after the student has become familiar with the present means of knowledge. Shell-making animals have been so little known, that we have no English word to express them. They are commonly called " shell- fah," because most of them live in the sea. "Fish" are, properly speaking, cold-blooded vertebrates breathing by gills. It is a strange assemblage which groups with these the warm-blooded whales ; the oysters and whelks ; the jointed craw-fish ; and the radiated star-fish. Just as we have been obliged to import the Latin word mammalj to include men, whales, bats and tigers, which are all warm-blooded, and suckle their young ; so we must import the word mollusk, to include snails arid slugs, oysters and clams, cuttles and tunicaries ; all of which agree in having soft bodies without jointed limbs ; the nervous system being irregularly distributed in knots, or ganglia, the principal of which surrounds the throat like a collar. In general shape, they are very dissimilar from each other. Some have a large head with staring eyes ; others are blind and headless. Some have many feet, others one, while whole classes have no organ of locomotion whatever. Some are so highly organized that many true fishes have to confess their inferiority : while some have special organs so little developed that it is doubtful whether they should be called degraded mollusks or superior zoophytes. It is by no means a necessary condition of a rnollusk to be shell- bearing. The lowest tribes have none ; in the highest they are only occasionaUor rudimentary, or are altogether absent ; the land and sea slugs are destitute of hard parts ; and some even of the bivalves are almost entirely horny. The name " shell-fish" therefore, as applied to the whole group, will have to be given up ; because myriads of species live on land and breathe air, and even the water species are not true fish ; and because a large proportion of them have no shells. Mollusks form one of the five great primary divisions of the Animal Kingdom. They rank side by side with the Articulata, or Jointed Animals, which include Spiders, Insects, Crabs, Worms, &c. The Sea- Worms, which have calcareous shells; and the Barnacles which formed part of the " multivalve shells" of Linnaeus, but which are now known to be degraded crabs, used to be considered mollusks, and are still seen in collections of shells.* Strange as it may seem, these apathetic creatures have much closer relationship with spiders and butterflies. The mollusks are specially designed for eating ; the artic- * The Cirripedes were thought by early naturalists to be the fry of Barnacle Geese. Very learned descriptions are on record, illustrated by figures accurately representing the author's imaginations, showing how the barnacles grew upon trees in the water, and at last came forth from their shelly eggs as full-flown birds. The reality is scarcely less surprising than the story: for it is now known that these creatures begin life as an active little crab, with legs, head and eyes all complete, swimming about in the open sea. Instead of developing how- 8 LECTURES ON MOLLUSCA. ulates for locomotion. The highest raollusks are superior animals to the highest articulates ; in both cases the lowest are inferior to many radiates. It is usual to rank them in parallel groups, thus : YERTEBRATA. MOLLUSCA. ARTICULATA. RADIATA. PROTOZOA. The VERTEBRATES include Mammals, Birds, Reptiles, Amphibians, and Fishes. The RADIATES include Sea-Urchins, Jelly-fish, Coral-insects, &c. The PROTOZOA include the simplest forms of animal life, such as sponges, animalcules, and Rhizopods or Foraminifera. These last were till lately ranked with the highest mollusks, because they make chambered shells. The principal classes of articulates have already been pointed out : those of the mollusks are as follows. I. CEPHALOPODS, or Head-footed Animals. II. GASTEROPODS, or Crawlers. III. PTEROPODS, or Wing-footed Animals. IV. LAMELLIBRANCHS, or Bivalves. V. PALLIOBRANCHS, or Lamp Shells. VI. TUNICATES, or Cloaked Animals. VII. POLYZOA, or Molluscan Zoophytes. We propose to give a general description of each of these classes, which are as different from each other as are beasts, birds, and fishes; and to furnish some account of the families and more important genera. The typical mollusks are the Gasteropods, of which Snails, Limpets, Whelks, and Cowries are familiar examples. In the same way the typical Articulates are not the highly organized Spiders, but the widely diffused Insects. We shall begin, however, with the less known and aberrant Cephalopods, which hold undisputed rank at the head of all invertebrate animals. CLASS CEPHALOPODA. (Cuttle-fish and their Allies.) Imagine a creature with two staring eyes, which he carries under his arms, and which are more complex in structure than those of many ever into something more perfect as do the caterpillars, tadpoles, &c., they lose not only their feet but their i-yrs and their very heads; adhere to rocks and sea-weed or floating timber; become almost shapeless lumps enclosed in an acorn or bnnmcle shell, only betraying their articulated origin by the delicate groups of feathery jointed cirri, by waving which they induce the tiny ocean c irrents which bring them th< j ir food. There was nothing but the resemblance of these cirri to the feathers of birds to form a groundwork for the goose story. LECTURES ON MOLLUSCA. 9 fishes. His nose is a long snout, or rather a pipe, which he wears under and between his eyes, as it were on his breast. He carries his mouth at the very top of his head, and could soon make one feel the bite of his powerful horny jaws, which are hooked, and work up and down like an eagle's. Although he has no legs, he is better off for arms than a monkey, having always eight or ten, sometimes a much larger number. These he elegantly arranges in a circle round his mouth; forming a crown more dangerous than the fabled hair of serpents round his head. His body appears only of secondary importance, and is inclosed in an oval or conical mantle, ending often in a tail like a fish, or adorned with fins, one on each side. Imagine this creature walking on his head, with his tail upwards, staring at you with both his eyes. As you watch him, he rapidly changes color, like a chameleon, by means of thousands of contractile pigment-cells all over his skin. He may change from yellow to red or brown, sometimes casting over himself a bluish tinge; the colored spots and waves appearing and disappearing with the greatest velocity. Though not a literary character, he always carries an ink-bottle, and generally a pen, alon^ with him ; and, should you chance to disturb him, he will instantly discharge a copious black stream before you, under cover of which he will dart off before you have time to follow his retreat. The Cuttles have very acute senses. They have an approach to a brain, inclosed in a cartilaginous skull. They can hear sounds, and evidently enjoy the taste of their food. They have a large, fleshy tongue, armed with recurved prickles, like that of the lion. They either crawl on their head, tail upwards, or swim, tail foremost, by striking their arms ; or squirt themselves backwards by forcing water forward, through their breathing funnels. They are ferocious creatures, the tyrants of the lower orders, and do- not scruple to attack and devour even fishes. The larger kinds are deservedly dreaded by man. Their weapons consist in their powerful arms, which are abundantly furnished with rows of cup-like suckers, each of which fastens on to its prey or its foe like a limpet to the rock. Often these are accompanied with sharp curved teeth, strong enough to be preserved even in the fossil species. "It must be a fearful thing/' says Dr. Johnston, "for any living creature to come within their compass, or within their leap, for, captured by a sudden spring of several feet, made with the rapidity of lightning, entangled in the slimy, serpentine grasp of eight or ten arms, and held by the pressure of some hundreds of exhausted cups, escape is hopeless." With such strength do they clutch the object of their desire that it is often easier to tear off the limb than induce them to relax their hold. They are the largest of all animals that are not supported by a jointed skeleton. One was seen in the equatorial Atlantic, which must have weighed two hundred weight. Another was seen in the Pacific, which must have been six feet long. As it is almost impossible to capture these great creatures alive, we remain in great ignorance about them. Montfort, one of the early conchologists, represented a "kraken octopod" in the act of scuttling a three-master; but he told his friend that, if this were "swallowed," he would in his next 10 LECTURES ON MOLLUSCA. edition represent him as embracing the Straits of Gibraltar, or capsizing a whole squadron of ships. The shell, in the typical Cuttle-fish, is not the hardened outside skin, as in ordinary mollusks; but, if present at all, is (with one exception) an internal appendage, answering the purpose of a skeleton, but having nothing to do with protecting the nervous centres. All the true cuttles and their allies have eight or ten arms, provided with suckers ; two gills, with superadded branchial hearts ; and a body shaped for an active, predatory existence. They form the OBDER I. DIBKANCHIATA, or two-gilled Cuttles of Prof. Owen. The first group are content with eight arms only ; the rest have, in addition, two long arms or ^ten- tacles," which serve to seize the prey at a greater distance. GROUP I. OCTOPODA. (Eight-footed Cuttles.) Most aberrant among these aberrant animals are the Family ARGON AUTIDJE, or " Paper-Sailors," so called from the delicate, white, boat-shaped shell, in which they were fabled to sail on the surface of the waters. The Argonaut was known to the ancients, one species being common in the Mediterranean. It was the First Nautilus of Aristotle, who, though generally so accurate, here invented or perpetuated a very pleasing fable. He described the Argonaut as sitting in its elegantly- keeled white and almost paper-like boat, holding up its two broader arms to catch the breeze, and using its other six as oars. In this posi- tion it is figured in all the older works on natural history : for either the authority of Aristotle, or the beauty of the story, caused it to be repeated from author to author, like the fable of the " Barnacle Geese." Even the naturalists of the present generation have gravely doubted whether the cuttle always found in the Paper Nautilus were the real former of the shell. A very similar shell, the Carinaria, or glassy nautilus, was known to be formed on a very different animal, a true Gasteropod. It was supposed that the greedy Octopod, having de- voured the Argonaut, possessed himself of the shell, after the fashion of the hermit crabs, which may be seen crawling, tail foremost, into shell after shell, till they find one to fit them. It was reserved for a lady to set these doubts at rest. Madame Power, finding the Argo- nauts common in the Mediterranean, inclosed a space with net work to allow free ingress to the water, and there established her colony. She found that the Octopod was the true inhabitant of "the shell, although not fastened to it by muscular attachment. She performed many experiments on her captives, the results of which have been either confirmed or corrected by succeeding naturalists. The Argo- naut generally crawls on the ground with her six sucker-covered feet, carrying her shell on her back, like a snail, enveloped in the two sails, or broader arms. When she chooses to swim, she does not float above the surface of the sea ; but darts through the water backwards, in the LECTURES ON MOLLUSCA. 11 direction of the nucleus of the shell, her sail arms still enveloping the frail bark. She generally folds her " oars" together, at arm's length, though she uses them occasionally to direct or assist her movements. What then is her propelling power ? She simply breathes herself on, or rather bloivs herself backwards, forcing out the water from her long gill-funnel, and so is carried forward in a contrary direction. She never turns her back on her enemy ; but, on the other hand, she can- not help looking back, wherever she is going. We say i( she;" for strange to say, all the paper-sailors turn out to be females. For a long time the lords of the Argonaut creation eluded the anxious search of their brethren of the human species. At last they were found in the form of little stunted octopods, without any shell or sail-arms, not more than an inch long. Let tyrannical husbands see what becomes of their sex in the very highest of the invertebrate animals. The male Argonaut is not known to hold any communication with his (to him) giant mate, who lives by herself in her palatial shell. The little fellow sends one of his arms, by itself, on the courting errand ; and the lady receives her spouse in the form of what was at first regarded as a parasitic leech. M. Koelliker found that what Cuvier had describee! as the Hectocotylus octopodis, was simply the contents of the left arm of the third pair on the male Argonaut, which is developed abnormally as a colored bag, and periodically gives birth to a Hectocotyle. This having been filled with spermatozoa from the body of the little Argonaut, goes forth on its independent existence, looking like an arm of an octopod ending in a thread. It lays hold on the female Argonaut with its suckers, as though it had a life of its own. It is found on her arms, clinging to her nose, or even inside the gill cavity. It clasps with such strength that it is difficult to detach it ; and yet it has no mouth or other organs for maintaining life. After it has communicated the fecundating influences to the ova, it perishes. It follows that the beautiful paper nautilus is not a true shell, but simply a female appendage to deposit and mature the eggs, and at the same time protect the parent. The newly hatched Argo- naut has no shell ; and is said to be shaped like a worm with suckers. This beautiful group belongs only to the existing conditions of our globe. One species alone is found fossil, in the Subappenine tertiaries of Piedmont. It is now living, but not in the Mediterranean, where it is displaced by another species : it has itself migrated to the present China seas. Family OCTOPODIDJE. The naked octopods resemble the male Argonaut ; and some (but not all) of them have the same singular degradation of the lordly sex. They generally have small, round bodies without fins, the head and arms being the principal part of the creature. They are seldom gre- garious, but crawl in the neighborhood of the shore, the small species inhabiting pools between tide marks. Here they escape detection by coloring themselves to suit the bottom, and moor themselves to crevices in the rocks awaiting their prey. They are more or less webbed between the arms, like an inverted umbrella ; and progress by flap- 12 LECTURES ON MOLLUSCA. ping the whole at once. They can crawl at the rate of seven feet a minute ; and when wishing to go quicker, they blow themselves out like a bladder, and roll over and over with great speed. They were called polypes by the Greeks; and some species bear a strong general resemblance to what are now called polypes, the jelly-fish, and their allies. The cuttles may be said to represent the radiates among the mollusks, but in their organization the} r are as different as birds and butterflies. The genera are Octopus^ Cistopus, Pinnoctopus, Ele- done, and Cirroteuthis. They differ in the arrangement of the suckers, and in the presence or absence of aquiferous pores in the skin and fins on the body. The Eledone moschata emits a strong smell of musk. The Cirroteuthis mulleri has its slender arms ciliated, with a web extending to their extremity. It inhabits the shores of Green- land. The Family PHTLONEXID.E differ from the typical octopods in being gregarious, living in the open sea. They hide themselves by day ; but towards evening come up in great shoals, to prey upon swimming mollusks and zoophytes. The genera are Philonexis and Tremoctopus. GROUP II. DECAPODA. (Ten-footed Cuttles.) These differ from the Octopods in having an additional pair of arms, much longer than the others, called tentacles. They are generally club-shaped at the end, and armed with a horny ring round the suckers, or sometimes with claws. They are within the circle of the eight arms, between the third and fourth pairs ; and are (for the most part) capable of being drawn in to pouches behind the eyes. The body is long, always finned, and strengthened by an internal appendage ; which is a horny pen in the squids, a " bone" in the true cuttles; a spiral, chambered shell in Spirula ; a complex organ with a cham- bered shell inside in the Belemnite tribe. The eyes are movable in their orbits ; the breathing funnel is generally provided with a valve ; and the mantle is supported by internal fleshy bands. Family CRANCHIAM. The Cranchia is a pot-bellied little creature, with very small head and eyes. These are covered by the skin; the mantle is supported by two internal fleshy bands ; and the breathing-pipe has a valve. Family LOLIGOPSID.E. (Calamaries.) In Loligopsis, which is a very long animal with a small head, the eyes are large and beautiful, and the breathing-pipe is without valve. Family CHIROTEUTHID^E. (Hand-Calimaries.) The body of the Hand-calamary, (Chiroteuthis,) seems only like a fulcrum, from which to move its powerful head organs. Though only two inches long, the arms are eight inches, and the tentacles extend LECTURES ON MOLLUSCA. 13 three feet. It must be remembered that these are not mere feelers, like the antennae of insects, but strong muscular threads beaded with suckers, and armed with four rows of pedunculated claws on the ex- panded ends. How easily these will encircle any unhappy creature floating at a distance, and carry it to the mouth, to be torn up by the horny bills, is at once evident. How so small a body can work the muscles at such a tremendous leverage, without any support but a loose horny pen, is indeed a marvel. The Veiled-calamaries, (Histioteuthis,) have six of their arms webbed together, leaving the other arms and tentacles loose. It resembles half an expanded umbrella. One of the species " rivals in color the brilliancy of the butterflies of tropical suns. The large membrane which unites its arms is of a rich purple, and the suckers are sapphire, the under surface being studded with blue and yellow spots on a reddish ground,, sprinkled with purple spots." Family ONYCHOTEUTHID^E. (Sea- Arrows.) These creatures have the mantle supported by three internal car- tilages. The eyes are exposed, and furnished with a slit above. The breathing-pipe has a valve, as in Cranchia. They are very numer- ous, and have been divided into the following genera : Enoploteutliis (Armed-calamary), AncistrocJieiruSj Abralia, Verania, Acantlioteutliis , (Spiny-calamary) ; Onychoteuthis (Hooked-calamary) ; Ancistroteuihis, Onychia; Ommastreplies (Sea- Arrows, or Flying-squids); and Tliysano- teuthis (Fringed-calamary). Among the active cephalopods, perhaps the most vigorous swim- mers are the Armed calamaries. They are the dread of the shell divers of the Pacific Islands ; for the arms have, beside the suckers, double rows of horny hooks concealed by retractile webs. A cat's paw is quite sufficiently disagreeable, with her five claws ; but for a bather to feel his naked body embraced with eight snake-like arms, with cat's-paw weapons on the whole length, and leech-like suckers in addition, to say nothing of the long tentacles still more powerfully armed,* and directed by two great staring eyes, much more service- able than a man's in the water, the possessor of which can instantly hide himself by a discharge of ink, is not pleasant even from a crea- ture the size of a cat : but when it is remembered that some of them are six feet across, and that they do not kill quickly like the shark, but tear their prey piecemeal, we feel thankful to live in safer lati- tudes. In the Hooked calamaries , besides the hook-armed cups, there is a group of ordinary suckers, at the beginning of the expanded part of the tentacles. When these touch each other, they resemble the hinge of a pair of pliers, and the unfortunate beast hooked in between the flaps is drawn by the united strength of both arms to be torn to death at the top of the cuttle's head. It is a merciful provision that his great eyes, so necessary for him in locomotion and attack, are spared the sight of the tortures he inflicts upon his prey. The hooks *The tentacle suckers of the calamary suggested the obstetric forceps of Prof. Simpson. 3M 14 LECTURES ON MOLLUSCA. found fossil in the German Jurassic strata, with the traces of the cut- tle itself, prove that the Spiny calamaries were equally the tyrants of the ancient seas. The Sea-arrows live in large groups in the open sea. They are themselves the prey of whales and birds. In order to avoid the attacks of their pursuers, they dart out of the water like the flying fish, often to such a height that they fall down on the decks of vessels. The eyes of these creatures have a deep lachrymal groove at the upper edge, and the ears are furnished with a longitudinal crest. Family TEUTHID^E. (Squids.) In the Squids the eyes are without lids, and covered with the skin, &s in Cranchia; but the mantle is strengthened with internal cartil- ages, as in the Sea-arrows. The genera are Gonatus, Loligo, Teuthis. Sepioteuthis , Rossia, Sepiola, and Fidenas; with the fossil remains of Leptoteuthis , Teudopsis, Beloteuihis, and Geoteuthis. The Squids form an important element in the North Atlantic fish- eries. The common Loligo is the favorite food of the Cod, and is therefore itself fished for bait. One half of all the cod taken on the banks of Newfoundland are said to be caught by it. "When the vast shoals of this mollusk approach the coast, hundreds of vessels are ready to capture them, forming an extensive cuttle fishery, engaging five hundred sail of French, English, and American ships. During violent gales of wind, hundreds of tons of them are often thrown up together in beds on the flat beaches, the decay of which spreads an intolerable effluvium around." They must themselves be consumed in enormous numbers ; for it has been estimated that a single squid will lay in one season forty thousand eggs. The pens of the squid tribe are loose supports in a pouch along the back. In old individuals, sometimes two or three are found laid together. They are analogous to the " bones" or steel plates in ladies' stays an instrument which ought not to be needed by a vertebrated animal. The Sepiolas are pretty little creatures, with round purse-like bodies, and a wing-like fin on each side. They live near shore, and may often be seen darting about in rocky pools. They are considered a delicacy in the South of France, where they are called supieta. The squids first make their appearance in the world's history during the epoch of the Lias and Oxford Clay. The octopods may, indeed, have existed, but their bodies have no hard parts that would be likely rto leave traces on the ancient rocks. Of the squids, not only the horny pens and claws have been preserved, but even the muscular mantle, the bottoms of the arms, and the ink bag filled with sepia which an artist might envy. They must have died a very peaceful death, as they always spill their ink under the slightest provocation. Some of the ink bags of the Lias are nearly a foot long, with a brilliant pearly coat. They probably formed part of the food of the formida- ble Ichthyosaurians of that epoch. Family SEPIAS. ("Drue Cuttles.) The Cuttle-fish proper are furnished with a "bone," which consists, on the back, of a hard, shelly dish, covered with membrane and end- LECTURES ON MOLLUSC A. 15 ing in a knob, and built up within with layer upon layer of very deli- cate wafer-like shelly plates, supported by numerous vertical pillars.* It is, therefore, very light and porous, at the same time that the shape and texture of the back give it great power of support. The cuttles are the least elegant of the tribe, having a large, flatish body, finned along the whole of each side. The knob, doubtless, protects the creature's tail from blows as it swims backward near the shore. The Chinese cuttle bones are sometimes eighteen inches long. Most persons have seen the delicate Spirula, transparent and white, shaped like a ram's horn divided across by pearly chambers. A mere conchologist would never suspect any close resemblance between this and the cuttle-bone. They are, however, so closely connected by in- termediate fossil forms, that, without a knowledge of their animal, it is difficult to say to which family these belong. No less different at first sight are the " thunderbolt stones," so common in the Jurassic and cretaceous rocks of Europe. In the world's history, they begin and end with these rocks. They were suddenly poured., in incalcula- ble abundance, on our planet ; and as suddenly they became entirely extinct. The Family BELEMNITID^E consisted of cuttles whose body was strengthened by a long pen, join- ing on, at the tail end, to a conical chambered shell, the air-cells of which were connected by a siphuncle at the side. This conical shell (formerly called the alveolus of the belemnite, and now known as the phragmocone,') was invested, at the tail end, with a longer cone or guard. This is fibrous, consisting of long prismatic cells, like the shell of the recent pinnas or the great cretaceous Inocerami, with which it entirely agrees in specific gravity. This guard is the " thun- derbolt stone" of the common people, and is generally preserved entire, while the chambers are often destroyed, and the pen has almost always perished. The most perfect specimens were found in the Oxford Clay, and are preserved in the British museum and in the cabinet of Dr. Man tell. Fragments of the chambered part, in the Lias and Oolite, are very like the then-extinct orthoceratites, though the animal is widely different. The last chamber alone sometimes measures six inches by two and a half; so that its cuttle must have been nearly three feet long. A fortunate breakage, in a specimen in the British museum, displays an ink-bag near the siphuncle, at once showing that it was an active swimmer, like the cuttles. The length of the guard is very variable in the same species, sometimes attaining to two feet. The septa frequently perish, leaving the chambers, which have been filled with calcareous spar, lying loosely on each other like a pile of watch glasses. The Belemnites were gregarious, and probably lived in a moderate depth of water. The classical writers before Pliny gravely supposed that they were the hardened contents of the bladder of the lynx; *This substance, when reduced to powder, is calleu pounce. Among other uses, when rubbed on paper after "scratching out," it prevents the ink from running. 16 LECTURES ON MOLLUSCA. whence they "btore the name lyncurium. The writers of the middle ages called them " ghosts' candles," "devil's fingers," " night mare's arrows," &c. The more learned supposed they might be petrified amber, fossil dates, stalactites, or spines of sea urchins. It was not till the beginning of the present century that their true nature was understood. The grooved Belemnitdla mucronata, which is charac- teristic of the chalk and Upper Green Sand, is found on both sides of the Atlantic. Although the Belemnite itself has not been found preserved, its next door neighbor, the Belemnoteutliis, has been discovered at Chip- penham, (England,) with its shell, muscular mantle, fins, ink-bag, funnel, eyes, arms, and horny hooks, all complete, as if thrown by the tide upon our present shore. The hooks are formidable weapons, from twenty to forty pairs appearing on each arm. In this creature the guard is very thin. In Conotenthis, an active swimmer of the Neocomian age, we have a very long pen terminating in a phragmo- cone shaped like a paper funnel; forming an exact transition from the Squids to the Belemnites. Family SPIRULIM:. The shells of Spirula are as common in tropical seas now, as were the Belemnites in those of the middle ages. Their resemblance to the pearly nautilus and other allied chambered shells, and especially to the fossil Gyroceras, or Crioceras, is very striking. Here is a loosely- coiled spiral shell, regularly divided by concave sejJta, like the Nauti- lus, each one pierced by a tubular siphuncle. But the resemblance is superficial only. The last chamber of the nautilus tribe is always large, and contains the animal, which is fastened to it by powerful muscles. Whereas the last septm of the Spirula is almost close to the margin, indicating that it is an internal shell, enveloped in the mantle of the cuttle-fish like the bone of the Sepia. Although the shell always forms part of the fancy collections from the Bahama Islands, and it is scattered by thousands on the shores of New Zealand, a perfect specimen of the animal has not yet been seen. It is, how- ever, formed on the usual decapodous type ; only the fins and arm-cups are very small. The ink-bag lies against the last chamber of the shell. Beautiful as the Spirula is, it is still more so when the outer coat on one side has been removed, by allowing it to float on dilute muriatic acid, so as to display the siphuncled septa. Among recent shells, the Spirula stands by itself; but it is connected with the Belemnites and Squids by fossil forms. In Spirulirostra, from the Miocene of Turin, we have a very loose spiral siphunculated shell immersed in a kind of cuttle bone of irregular shape. In Bellop- tera, a fossil of the Nummulite age, the chambered part- is nearly straight, and surrounded by a "bone" formed by two inverted cones with winged processes between. In Belemnosis, a unique fossil of the London Clay, the bone is not winged. In Helicerus, a fossil described by Professor Dana from the slate rocks of Cape Horn, there is a guard, as in the Belemnites, inclosing a chambered shell somewhat spiral at the nucleus. LECTURES ON MOLLUSC A. 17 ORDER II. TETRABRANCHIATA, or four-gilled cephalopoda, of Professor Owen. It might be thought a matter of little importance whether a cephalopod had one or two pairs of gills ; but it happens that this difference is coordinate with others that run through the whole form and structure of the animals. The two-gilled cuttles, we have seen, are adapted for an active and predacious life. As they could not dart after their prey carrying a heavy shell, they are naked, but furnished with powerful arms and ink-bag for their protection. The four-gilled tribes, on the other hand, are destined for a quieter life, crawling on the ground like common Gasteropods. Instead of eight or ten arms with suckers and hooks, they have a multitude of small retractile feelers, something like the Sea Anemone. On these they can creep, and draw their prey to their mouths ; but they are not able to pursue it in the open sea. Instead of a strong breathing tube with a valve, answering the purpose of a forcing pump and propeller, they have only an open gutter made by a fold in the mantle, like the siphons of the Gasteropods. The eyes, which in the cuttles have optic ganglia much larger than the central brain, (Alcock,) are here less conspicuous, and mounted on peduncles. The head and tentacles, instead of being the principal part of the creature, to which the body might appear subordinate,, are here scarcely separated from it, and retractile within the general mass. They are always furnished with a chambered shell, the last cavity of which contains the animal. When disturbed, instead of squirting ink and darting off, it shrivels up into its cavity and takes its chance. If it sees a delicate crab at a distance, instead of pouncing on it, it must crawl, not, indeed, on "all fours," but on "all dozens;" or wait until the creature comes within seizing distance, when it will be entangled in the arms and be broken up by the jaws or gizzard. Only one animal formed after this type is now known to be living on the earth; the pearly or true Nautilus, whose many-chambered shell has been an object of admiring speculation from early times. This is the last straggler belonging to a race which performed import- ant functions in the early ages of our globe. The Nautili themselves are among the few genera which have existed at every period of the world's history. Our knowledge begins with one species from the upper silurian rocks of Bohemia. It has not culminated at any par- ticular period ; not more than seven species appearing in any forma- tion ; but it has never been without its representatives, and two or three species are now crawling on the sea bottoms in the East Indian archipelago. Before them, however, lived the great Orthoceratites of the palaeozoic seas ; and as they died out, the great family of the Am- monites developed themselves, and held possession of the seas till the close of the cretaceous period, when they suddenly disappeared, leaving not even a distant relation to grace the tertiary formations. Coordi- nate with the prevalence of four-gilled Ceplialopods, we find a general absence of the predacious Gasteropods which are now so numerous and highly developed. We may suppose, therefore, that they played the same part in the economy of nature ; and that the Orthoceratites and 18 LECTURES ON MOLLUSCA. Ammonites did the work of destruction in ancient times, which is now performed by murices, strombs, whelks, and their allies. The chambered shell is always pearly within, but with an external p^rcellanous layer. The Chinese are fond of leaving patterns carved on the Nautilus while the body of the shell is uncoated, to show the nacre. In fossils sometimes the outer coat has perished, sometimes the inner, and sometimes both. The chambers are always connected by a siphuncle, through which the animal maintains a connection with the deserted chambers. These are lined with a very thin living membrane in the Nautilus; in the Orthoceratites they show the marks of blood- vessels, &c., which prove that they played some unknown part in the economy of the animals. That these air-chambers serve as a float, to balance the weight of the shell and enable the creature to swim if needful, cannot be doubted ; but the stories of their filling the cells with air or water at pleasure, and so sailing at the top or descending to the bottom, appear to be fables, like the classical legends of the Argonaut. The living Nautilus only comes to the surface occasionally, when the sea bottom has been agitated by storms ; and it is believed that the fossil species inhabited depths not greater than thirty fathoms. The chambers are filled with nitrogen gas, without oxygen or carbonic acid. The animal is attached to the shell by powerful adductor mus- cles. As these grow onwards, the animal gradually deserts the last chamber; and, at periodic periods of rest, a fresh septum is formed.* If a diving bell had explored what is now called New York and *The following lines have the rare merit of not losing truth at the same time that they are highly poetical. They are copied from the "Atlantic Monthly." Let the reader take in his hand a pearly Nautilus cut through the middle, and say This is the Ship of Pearl, which, poets feign, Sails the unshadowed main; The venturous bark, that flings On the sweet summer wind its purpled wings, In gulfs enchanted, where the siren sings, And coral reefs lie bare; Where cold sea-maids rise, to sun their streaming hair. Its web of living gauze no more unfurl ; Wrecked is the ship of pearl! And every chambered cell, Where its dim, dreaming life was wont to dwell, As the frail tenant shaped his growing shell, Before thee lies revealed; Its irised ceiling rent, its sunless crypt unsealed! Year after year behold the silent toil That spread his lustrous coil; Still, as the spiral grew, He left his past year's dwelling for the new; Stole, with soft step, its shining archway through; Built up its idle door, Stretched in his last-found home, and knew the old no more. LECTURES ON MOLLUSCA. 19 Canada when they lay at the bottom of the palaeozoic seas, it would have encountered multitudes of long pointed shelly cones, floating upright in the water, some of them adorned with beautiful colors and sculpture, and slowly moving among the corals, sea-weeds, and stone- lilies which then adorned the gardens of the great deep. They be- longed to the Family ORTHOCERATID^:, or Straight-horns. Some of them carried on their backs the largest shells that ever lived. A specimen belonging to Col. Jewett, of Albany, now measures twelve feet, and when perfect must have been fifteen feet in length. And yet, from the buoyancy of its contained air, the com- paratively feeble cephalopod could maintain its enormous leverage, and crawl on its slender tentacles. The aperture of the Orthoceratites is generally contracted, and the head was perhaps always exposed. The siphuncle is very large, and in some of the genera very curiously formed, indicating much more vitality than in the corresponding part of the Spiral Nautilus. This was necessary in order to maintain a living con- nection at such a distance from the body. All the orthoceratites have simple, concave chambers, with a central opening. They disappear at the beginning of the secondary rocks, leaving their work to be per- formed by the huge Ammonites of the Lias. In Gonioceras, the shell is flattened, and the septa waved. In Actinoceras , Hormoceras and Hu- ronia, the siphuncular processes are enormously developed around the central tube, according to different patterns. In Thoracoceras and Cameroceras, the siphuncle is marginal, and generally small. The strange fossils called Endoceras by Prof. Hall have very long slender shells, with a large cylindrical siphuncle, somewhat lateral. This is thickened internally by separate layers of shell, or funnel tubes one inside the other, called " embryo tubes" by the author, contrary how- ever to all analogy. Their use may have been to give increased strength in consequence of the great elongation of the shell. Some of the species appear to have been constituted from the accident of a young shell being lodged in the siphuncular cavity : others from the monstrous formation of a second siphuncle. Thanks for the heavenly message brought by thee, Child of the wandering sea, Cast from her lap forlorn ! From thy dead lips a clearer note is borne Than ever Triton blew from wreathed horn! "While on mine ear it rings, Through the deep caves of thought I hear a voice that sings: Build thee more stately mansions, my soul, As the swift seasons roll! Leave thy low-vaulted past! Let each new temple, nobler than the last, Shut thee from heaven, with a dome more vast; Till thou at length art free, Leaving thine outgrown shell, by life's unresting sea! 20 LECTURES ON MOLLUSCA. The Phragmoceras and Oncoceras form a sub-family, in which the shell is pear-shaped and contracted at each end. The bent forms constitute another sub-family, and were perhaps more nearly related to the Nautilus. Cyrtoceras is slightly curved, and shaped like a gigantic Caecum.* Gyroceras dev elopes a shape like Spirula ; and Ascoceras displays a shell bent upon itself, like PtycJio- ceras among the Ammonites. Family In the living Nautilus, the only interpreter of the great group of Tentacular Cephalopods (as D'Orbigny calls the order) the horny beaks are surrounded with shelly matter, giving them great crushing power over the shells of crustaceans. Similar beaks have been found fossil in various strata, associated with Nautili. In the Muschelkalk of Ba- varia, where there is only one species of Nautilus, the upper beak has been described as Eliyncolites hirundo, and the under beak as " Con- chorliyncus avirostris." D'Orbigny has turned these mandibles into cuttle bones, under the names of JRJiyncoteuthis and Palceoteuthis ; one out of the many instances in which a knowledge of comparative anat- omy is shown to be essential to the study of organic remains. Kound the mandibles is a circular fleshy lip ; round which again are about four dozen labial tentacles, answering to the " buccal membrane" of the cuttles, and serving to bring the prey to the mouth. Beyond these are a double series of tentacles, thirty-six in number, answering to the ordinary arms of the cuttles. When the creature is expanded for crawling or seizing prey, these would project somewhat in the form of a figure 8, the mouth being between the two groups of tentacles. When the creature retires into its shell, it protects the opening with a hood, which answers to the back pair of arms, united together and developed for that purpose, as are one pair in the female Argonaut to envelop the shell. The tentacles shut up in bunches into sheaths, which correspond to the eight common arms of the cuttles. Besides these there are four tentacles, one on each side of each eye : these appear to be feelers as in the Gasteropods. It is easy to see how much more highly organized and active is the paper, than its distant relative the Pearly Nautilus. In each case, all the animals examined have been females. It has been supposed that the shell-forms with a wide open- ing at the axis of the spire, belong to the males, which, as in the other Cephalopods, are few in number. Similar differences are found in almost all the Ammonites. The Fossil Nautili present several sections, differing more or less in type from the recent species. In Cryptoceras, the siphuncle is nearly external, as in the Ammonites, which it resembles in external form. In Temnocheilus, the shell is carinated. In Discites all the whirls are exposed and flattened. These sections are from the palaeozoic rocks. The " Ellipsolithes" were simply Nautili and Ammonites which had been accidentally compressed into an oval shape. ' The Corniculma figured by Munster as a chambered shell, is probably only a badly observed Caecid. LECTURES ON MOLLUSCA. 21 In the Lituites of the ancient seas, we have a Nautilus, which, on coming to maturity, produced its tube in a straight line. The Hortolus resembles it, but with the whirls separate as in Spirula. In TrocJioceraSj we find the spire more or less elevated, as in snails. The sub-family CLYMENIDJE consists of forms in which the chambers are more or less waved or indented, forming a slight approach to the Ammonites. They are all palaeozoic forms, except Aturia, which makes its appearance unexpectedly in the London Clay. This has a very large internal siphon, like a number of funnels interwrapping each other, and reminding us somewhat of Endoceras among the Orthoceratites. Family AMMONITID^E. (Bam's-Horn Shells.) This group, so abundant in the middle ages both in species and in individuals, suddenly passed out of existence at the close of the creta- ceous age. The body of the Ammonites was long in proportion : the opening of the shell was guarded by curiously-shaped processes, and closed by a double operculum. In the beautiful flat Ammonites of the Oxford Clay, the shell makes two long forceps-shaped beaks, one on each side of the mouth. In another species, these beaks arch over the mouth and meet in the middle, leaving one hole for the head to crawl out at, and the other for the opercle-bearing arms. In other species, the aperture is almost closed up, as in many snails. In the keeled species, the operculum was of one horny piece, as in Gasteropods : but in the round-backed groups, it was shelly, and divided into two plates. Forty-five kinds have been described, one being from the paleozoic rocks. They were called Trigonellites by the old writers, and doctors still disagree as to their nature. D'Orbigny thought them cirripedes : Meyer, bivalve shells : Sowerby, fish palates : Deshayes, gizzards of Ammonites : Coquand (followed by Chenu) cuttle bones. They have however sometimes been found in situ, exactly answering to the hood of the Nautilus. But the most remarkable character of the Ammonites is the sutures, or edges of the chambers. When an Ammonite is sliced down the middle, the septa simply appear waved as in Clymene. But when the outer shell is removed, and the cast of the edges is displayed, we find a beautiful leafy structure, often of very intricate pattern, but constant in each species. The siphuncle is always external. The outside is almost always very beautifully ornamented, with ribs, knobs, spines, or delicate stria?. The under layer is always pearly, as in Nautilus ; and beautiful objects they must indeed have been, when painted with vari- ous colors and patterns, to those who could have seen them with oolitic or cretaceous eyes. Some of them are of enormous size, meas- uring occasionally two feet in diameter. These are found in the Lias, and in the neighborhood of Bristol (England) may often be seen built into the walls by the road side. More than five hundred and thirty species are already known. They are rare in America, but very com- mon in Europe. Species, similar to those of the English oolite, have been found in the high passes of the Himalaya, more than 16,000 feet above the level of the sea. The most ancient of the tribe are the Gomatites, of the Upper Silu- 22 LECTURES ON MOLLUSC A. rian and Carboniferous seas. In these, the sutures are not foliated, "but simply lobed, often at sharp angles. In the ceratites of the Mus- chelkalk series, the alternate lobes are denticulated. The Goniatite, when the spire is unrolled into a straight cone,, like the Orthoceratites, becomes a Bactrite; and the Ceratite, similarly unrolled, becomes a Baculina. The true Ammonites, with minutely lobed septa, present all varieties of shape ; from the compressed forms, with the whirls scarcely touch- ing, to the involute species, with round backs, narrow chambers, and very small umbilicus. They have been variously divided into groups by different authors ; but they pass into each other by very slight dis- tinctions. Often a shell, which in its earlier stages would belong to one group, develops into a different one as it approaches maturity. The Ammonites present various aberrant forms, some corresponding to those already mentioned among the Nautili, some peculiar to them- selves. In Crioceras the whirls are separate, as in Spirula. In ScaphiteSj the shell begins like an Ammonite,, the mouth is next pro- duced at a tangent, and then bent back upon itself. It would be curi- ous to know how such creatures got their living. Ancyloceras com- bines the characters of the two last genera, beginning as Spirula, and ending as Scaphites. Anisoceras has the same form, but drawn out of the plane into an irregular spiral, like Vermetus. Toxoceras presents a simple cycloidal curve. In Hamites, the shell begins quite straight, then bends and returns again parallel to itself, and so on, like a Spi- rula drawn out and flattened on its two sides. In the section Hamu- lina, the shell only makes one bend, the two parallel limbs having different sculptures, and the body-chamber occupying one limb and the elbow. The Ptychoceras is like a Hamulina, with the two limbs joined together ; still with different sculptures, so that fragments might easily be described as distinct species. In Baculites, the shell is quite straight, like a walking stick. It is so common in the Nor- mandy chalk as to give it the name of Baculite 'Limestone. In the Terrilite group, we have an approach to the ordinary shape of the univalve spiral shells. They are mostly reversed, and are sup- posed by Woodward to have had one pair of gills atrophied. In HeteroceraSj after beginning as a Turrilite, the shell becomes separate, as in the adolescent Vermetus, and makes an irregular spire eveloping, but not touching, the spire. The Helicoceras is as it were a Turrilite, with all the whirls drawn out into a corkscrew. We have now enumerated the principal known forms of Cephalo- pods, both extinct and living. While they are the most highly organized of invertebrates, they cannot be considered as typical mol- lusks; that is, they do not represent the idea of molluscan life, as do the ordinary Gasteropods which we have next to consider. Now those classes which go off from the standard idea are generally pretty well defined ; while those in which the normal idea culminates are more variable in structure. We have seen that the cephalopods are all formed on two well-marked but distinct types ; and however much the shell of the Baculite may differ from the Nautilus, or the Argonaut's egg-case from the cuttle-bone, a beginner even could never doubt con- LECTURES ON MOLLUSCA. 23 cerning the class of a cephalopod if he saw it alive : for though star- fish and polypes, as well asBryozoa, have a central mouth surrounded by arms or feelers, the great eyes and funnel, as well as the soft but muscular body, would at once assign its position. It is not so with the Gasteropods. To say nothing of the different shapes of the shell, as e. g. in Chiton, Dentalium, Patella, Trochus, Vermetus, Cypra>a, Murex, and Carinaria, the shapes of the animals are so very unlike that even now naturalists are not agreed as to the limits of the class ; still less on the arrangement of its fundamental divisions ; least of all, on the position of particular families and genera. This should by no means discourage the student ; but on the contrary fill him with zeal to prosecute a study in which so many unworked materials are within his own reach ; and in which, therefore, instead of merely following at a remote distance in the steps of the learned, he may, without neglecting the main duties of his life, add materially to the stores of human knowledge, and even throw important light on the dark places of our planet's ancient history. CLASS GASTEROPODA; that is, belly-footed animals, or crawlers: comprising snails, periivin- Ides , ivhelks , limpets, and " univalve shell-fish' ; generally. These creati^es form three-fourths of the whole number of mollusks. They inhabit sea-shores, and the sea-bottoms, down to the lowest depths of ordinary animal life : they are found swimming in the open seas, or accompanying the floating gulf weed : or they live in fresh waters, crawling on stones or aquatic plants. Lastly, they are found on dry land, in all kinds of situations where lime exists ; either in damp and marshy places, or in rocky deserts ; either burrowing in earth or crevices, or creeping on the vegetation of forests, herbage, or lichen-covered stones, One cannot live anywhere, therefore, where crawling mollusks are not within our reach. The following classifi- cation may aid us in understanding these many-shaped creatures : Class. Stib-classes. Orders. Examples. f PECTINIBRANCHS... Whelks, Cones, Strombs, Cowries, Peri- PROSOBRANCHS . . .