NOTES ON SOME CRUSTACEANS FROM THE CHEMUNG 
 
 GROUP OF NEW YORK. 
 
 By JOHN M. CLARKE. 
 
 [From 15th Annual Report of the State Geologist.] 
 
NOTES ON SOME CRUSTACEANS FROM THE CHEMUNG 
 
 GROUP OF NEW YORK. 
 
 By JOHN M. CLARKE. 
 
 72^9 
 

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 Notes on Some Crustaceans from the Chemung Group of 
 
 New York. 
 
 John M. Clarke. 
 
 5 - 
 
 15 
 
 Q<- 
 
 I. A Singularly Ornamented Phyllocarid Genus, Pephricaris. 
 
 By the courtesy of Professor A. B. Crandall, of Alfred university, 
 Alfred, N. Y., and the kindness of Mr. Charles Butts, of the same place, I 
 have been permitted to study specimens of a new crustacean allied to Eclii- 
 noearis^ but noteworthy for the extravagant nature of its armature. Of these 
 specimens, two in number, the more complete belongs to the museum of 
 Alfred university and is a sculpture-cast of essentially the entire test, the 
 valves of the carajDace being expanded without distortion and the abdominal 
 segments showing, in part, in the posterior hiatus of the carapace valves and 
 thence normally protruding behind. The second specimen, the property 
 of Mr. Butts, is only the echinate margin of one carapace valve. 
 
 The general aspect of the carapace is not -unlike that of some species of 
 Ecliinocaris^ yet it is devoid of the curved sigmoid carina which characterizes 
 typical species of that genus. 
 
 The carapace valves are broad, their margins curving rapidly outward 
 for about one-half of their length, slowly i*ecurv- 
 ing near the middle and thence more rapidly 
 receding to the posterior extremity. The expanded 
 valves lie with a moderately broad anterior or 
 rostral cleft, but there is no evidence of a separate 
 rostral plate. They are in contact just back of the 
 apex of this cleft, but for only a short distance, as 
 the underlying abdominal segments are partly 
 exposed, a fact which may be due either to this 
 being the normal attitude of the valves, or to casual 
 separation of them, or again to a breaking of the 
 edges of the cast which is not altogether clear at this 
 place. The surface of each valve is divided into two convexities by an oblique 
 depression beginning at the dorsal edge just back of the middle and extend- 
 ing backward \vith gentle obliquity. This groove does not reach the margin 
 
 Figure 1. 
 
 Pephricaris horripilata, Chemung 
 samLstone, Alfred, N. Y. 
 
732 
 
 Refokt of the 8 fate GEoLu(usr. 
 
 of the valve. The anterior convexity is much the larger. Usually, in JEchi- 
 nocaris. there is a number of paired nodes and tubercles grouped about the 
 cephalic extremity of the carapace, but in this fossil there is only a single 
 [)air, represented by two deep pits situated close* upon the hinge and at the 
 apex of the rostral cleft. It is possible that these are remains of ocular 
 nodes, but theii* depth suggests the probability of their having been basal 
 attachments of the larger legs. Behind these nodes begins an ol)lique and 
 strong ridge, thickest and most elevated at the hinge, where the anterior 
 edges of the ridges on the two valves meet. This ridge departs backward 
 into the median groove, passes down its anterior slope, then, with a slight 
 change of angle, along the groove and rises slightly on its opposite slope, 
 terminating with the groove itself. The margin of the carapace is some- 
 what thickened and elevated. 
 
 Nowhere in do w e find a carapace structure like this, even 
 
 among the species of the Chemung group. The lateral curved carina is one 
 of the constant characters of the genus and may even be duplicate in later 
 species. The median sinus exists there, normally, only as a depression 
 betw'een nodes, and no species is so free of cephalic nodes as this. 
 
 As to the abdominal segments, Ave find that three, and a portion of a 
 fourth, protrude beyond the carapace ; between the carapace- vah^es Ave make 
 
 Figure 2. 
 
 Pephricaris horri- 
 pilata, margin of 
 left valve. 
 
 spines. These are shortest at their commencement on the anterior margin, 
 gradually increase in size posteriorly, their greatest length being reached 
 on the post-lateral curve, and thence to the posterior angle of the 
 carapace they liecome shorter. The maximum length attained by these 
 spines is not less than one-half of the greatest diameter of a carapace vah^e. 
 That these processes are spinous extensions of the chitinous test substance, 
 and not liiindles of setje, or of other nature, is shoAvn by the aspect of the 
 im})i*ints they have left in the matrix, these being sharply defined 
 
 out traces of tAvo or three others, estimating the entire 
 number at seven. The posterior segments are unusually 
 short and haA^e short spinules at their post-lateral extremi- 
 ties ; there may, also, have been such spinules elseAvhere along 
 the posterior edge as in Echinocaris, but such are not seen. 
 The caudal plate is short and triangular, Avith a short telson 
 and tAVO long curved cercopods. 
 
 The fossil bears a striking ornamentation or armature. 
 The entire outer margins of the carapace valves carry a 
 single roAv of broad, strong, erect and slightly recurAung 
 
Clarke — Crustaceans from the Chemung Group. 
 
 788 
 
 and clean-edged throughout their extent ; and again by the presence of similar 
 but straighter and more slender spines upon the final segment of the abdomen. 
 Of the latter, two pairs are visible, the penultimate pairs appearing to be 
 somewhat longer than the ultimate ; there are traces also of a similar pair on 
 the antepenultimate segment. 
 
 This description presents all the known characters of this peculiar 
 crustacean. Its essential structure is nearest to Echinocaris and yet not in 
 harmony with that genus, and its extravagant decoration emphasizes that 
 generic difference. For this reason the generic term Pephricaris is adopted 
 for the fossil, and the species may be known as Pephricaris horripilata. 
 
 Both specimens of the species were found in loose blocks of compact 
 Chemung sandstone at Alfred, N. Y. Neither shows associated fossils. 
 
 II. The Chemung Trilobite, Bronteus senescens, Clarke. 
 
 In the Report of the New York State Geologist for 1888, the writer 
 described the trilobite above named.* The single specimen upon which the 
 description then published was based, was but a very imperfect fragment of 
 a pygidium and the only justification for drawing attention to the fossil was 
 the extreme rarity of all trilobites in the Chemung faunas. At the date of 
 that writing the presence in the Chemung of the species Phacops rana. Green, 
 common in the Hamilton rocks beneath, and not of infrequent occurrence in 
 the Ithaca fauna immediately below the Chemung formation, was suspected, 
 and had been announced. Later evidence has not confirmed this statement, 
 and we know to-day only two described species of trilobites from this fauna ; 
 the Cyphaspis lcevi% Hall (sp.), the original and only known specimen being 
 a cephalon, and Bronteus senescens. The presence of the genus Homalonotus 
 is shown by a fragment from the higher beds in Alleghany county. Since 
 the description of Bronteus senescens^ founded on a specimen from the lower 
 Chemung strata in the town of Prattsburgh, Steuben county, additional 
 material has been obtained which sets forth the characters of the species in its 
 entirety and also shows that from the fragment previously figured and the 
 restored outline at that time given to the pygidium, it might prove difficult to 
 recognize the species when at its best. A restatement of the characters of the 
 fossil drawn from our amplified knowledge of it, will therefore serve to clearly 
 define the value of this species. 
 
 * The Genus Bronteus in the Chemung Rocks of New York, op. cit.., Figure 1 ; also published in Forty-sec»^nd Annual Report 
 Trustees State Museum, pp 403-405. 
 
734 
 
 Report of the State Geologist. 
 
 ' Soon after the publication of the article above cited, the writer located 
 the horizon at which this fossil occurs, on Bardeen’s farm in the northern 
 part of the town of Prattsburgh, finding here several nearly entire pygidia. 
 This horizon is well characterized by the constant association of this trilobite 
 with the Arthrdcantha deprema ; a species recently described by 
 
 W achsmuth and Springer from specimens collected at this locality where its 
 S 2 :)inous plates are very common. It is the zone of Wt t/nchonella {Pucjnax) 
 pucjivm^ Sow., and is an eastward extension of this zone from its somewhat 
 moi'e prolific manifestation at High Point, in the town of Naples. More 
 recently two essentially entire specimens of the trilobite have been obtained 
 from higher strata of the Chemung group, near Avoca, Steuben county, 
 through the agency of Mr. Clifton J. Sarle, both excellently preserved though 
 lacking a few details, but presenting us with a reall}- striking exempli- 
 fication of the late continuance of this genus. 
 
 Figures of these specimens are here given and the description of the 
 characters of the species is as follows : 
 
 Figures 3 and 4. Bronteus senescens ; two nearly entire individuals from the Chemung group, 
 
 near Avoca, N. Y. 
 
 General Proportions. The outline of both of these extended 
 individuals is quite regularly ovo-elliptical, the shorter curve being at the 
 posterior extremity. In length the larger measures 54 mm., the smaller, 46 
 mm., AN'hile the greatest width of the animal is about one-half this dimension 
 in b(.)th cases. The specimens have been subjected to slight, if any, vertical 
 compression though the heads are some^vhat askew ; the lines of the margin 
 may, therefore, be regarded as normal. 
 
Clarke — Crustaceans from the Chemung Group. 
 
 735 
 
 Cephalon. The head is short and subsemilunar in outline, the posterior 
 margin being quite direct. Its length is slightly more than one-half its width. 
 The genal angles are somewhat produced into short and broad spines. The 
 margin is elevated, while the border of the head is broadly concave, rising on 
 its proximal limb to a genal ridge. The eyes are small, well back on the 
 cheeks and moderately elevated, the surface between the palpebrum and the 
 <iorsal furrows being notably convex. The facial sutures are normal. 
 The glabella is elongate and clavate, its width at the anterior extremity 
 where it reaches but does not overhang the margin, being twice that just in 
 front of the occipital ring. In contour it is depressed convex, though its 
 elevated median portion attains greater elevation than any other part of the 
 cephalon. The dorsal furrows are deep and narrow; starting from the 
 posterior margin they approach each other rather abruptly ; the curve changes 
 at the level of the posterior part of the eyes and thence forward the furrows 
 diverge outward rather gradually, broadly recurving near the anterior margin. 
 The lateral furrows are short but distinct, the first and third pairs being 
 most clearly defined, a median pair making but a gentle depression upon the 
 surface, while the occipital groove is broad and shallow. 
 
 The occipital ring is likewise broad and distinct, but its prolongation to 
 the cheeks is narrower and much more faint. 
 
 In one of th^ specimens the removal of the j)art of the glabella has 
 exposed a portion of an elongate liypostome with an oval central depression, 
 surrounded by a narrow regular groove and bordered by a narrow flattened 
 margin. 
 
 Thorax with the normal number of ten segments. The axis is very broad, 
 having fully one-third the entire width of the thorax, and its margins curve 
 outward, approaching each other posteriorly. On the axis the segments are 
 moderately broad and flat, distinctly elevated along the median line with 
 general longitudinal depressions on the lateral slopes and a slight anterior 
 bend at the sides. On the pleurae, the segments are narrow and soon become 
 free of each other, tapering rapidly to slender, recurved, acute extremities. 
 
 PvGiDiUiVr semielliptical, fiabelliform ; length and width about ecpial. 
 Axis very short, extending for not more than one-fifth or one-sixth of the 
 plate ; triangular, elevated medially and with an obscure centra] lobe and 
 depressed lateral slopes. The pleura) are broad, flat, separated by sharpl}' 
 defined flat grooves. They broaden rapidly outward and finally become 
 merged into the grooves near the periphery of the plate, so that the margin of 
 the latter is smooth. These ribs are fifteen in number; the median ril) l)eing 
 
736 
 
 Report of the State Geologist. 
 
 somewhat broader than the rest and, in the larger specimen, showing a 
 tendency to division along its distal portion. The margin of the pygidiiim is 
 without evidence of spines. In general contour this plate is broadly depressed 
 within the slightly elevated periphery, convex over the central region and 
 again sharply depressed about the axis. 
 
 Orxa:\ientation. The entire test is pretty uniformly pustulose, the 
 pustules varying somewhat in size and being coarsest on the glabella and the 
 ribs of the pygidium. About the enfolded margins of the cephalon and 
 pygidium the surface is marked by the usual incised inosculating lines. 
 
 Observations. This species is noteworthy not alone for the rarity of 'all 
 trilobites at this horizon. It is, in all probability, the latest representative 
 of the genus, making its appearance in this later division of Devonian time, 
 subsequent to the first intrusion of Spirifer disjurictus and long after the 
 only observed occurrence in this country of Clymenia. It appertains to a 
 fauna which, considered in its local I'elations and in correlation with faunas of 
 other countries, characterizes the final stages of the Devonian, and in these 
 we have no other record of the occurrence of Bronteus. In this late survivor 
 of the genus, therefore, we may expect to find structural traits indicative of, 
 or in harmony with its late appearance. W e observe that between the earlier 
 (upper Silurian and early Devonian) and the later Devonian representatives of 
 this genus there are contrasts in the form of the glabella, the outline of the 
 pygidium and the nature of its ribs. Thus, the glabella (or we should rather 
 say the cranidium, as the distinction depends on the varying distance between 
 the facial sutures) is very wide anteriorly, the dorsal furrows being highly 
 concave within the ocular nodes (compare B. palifer^ Beyr., Lower Devonian, 
 Zittel’s figure, Grundzlige der Palaeontologie, p. 473, fig. 1,279a; Katzer’s 
 figure, Geologie von Bohmen, p. 1,023, fig. 498-4; B. (ximpanifer, Beyr., 
 lower Devonian. Beyrich’s figure, Einige bohmische Trilobiten, Plate, fig. 6 ; 
 B. Partsch% Barr., upper Silurian, Katzer’s copy of Barrande’s figure, op. city 
 p. 937, fig. 377-2 ; B. viator., Barr., lower Devonian, Novak’s figure in 
 Katzer, op. cit., p. 1,036, fig. 548-1 ; B. acarnas., Hall, Niagara group. Twentieth 
 Annual Report New York State Cab. of Natural History, PL II, fig. 19 ; 
 B. Iwnatu.s. Billings, Trenton limestone. Geology of Canada, p. 188, fig. 187, 
 and Clarke’s figure. Geological Survey of Minnesota, Vol. HI, Part 2, p. 725, 
 fig. 43). In all of these and numerous other recoi*ded examples the feature 
 i*ef erred to is strongly manifested. If on the other hand, Ave turn to species 
 of the middle Devonian, the nai*i*owing of the glabella and the interval 
 between the facial sutures becomes evident (see B. -jiahellifer^ Gold fuss, 
 
Clarke — Crustaceans from the Chemung Group. 
 
 737 
 
 System. Uebersicht, PL VI, fig. 3 ; B, nieri(lio)iali% Trom. and Grasset, 
 Barrois’s figure, Calc, k Polypiers de Cabrieres, Plate I, figure 2a • 
 B. thysanopelti.% var. Waldsdimidti,, v. Koenen, Waldsclimidt’s figure, Zeitschr. 
 d. d. Geol. Gesellsch., Vol. XXXVII, PI. XXXVIII, fig. 2 ; B. senescens, etc., 
 etc.). This feature appears to be one which, irrespective of other variations 
 in structure, has gradually passed through the change noted, and it is, 
 naturally, to be observed that lower Devonian faunas embrace species, some 
 with the wide, some with narrower glabella, while thereafter, the earlier 
 type of glabella has disappeared. 
 
 With reference to the characters of the pygidium in this genus it may be 
 remarked that the only really useful, tenable subdivision of the group is 
 founded upon the presence of spinules upon the pygidial margin. This is 
 Thyanopeltis^ one of the names introduced by Corda and designed by its 
 author to include species of this character; it has proven to possess a definite 
 stratigraphic value. In matter of outline there is considerable variation, from 
 the subsemicircular shape in the earliest species like B. lunatm^ Bill., of the 
 Trenton, B. laticauda^ Wahlenberg, of the lower Silurian of Sweden, and B. 
 hihernicus, Portlock, of the Caradoc, to the elongate-elliptical curve presented 
 by the species of the Devonian. In this feature B. senescens is extreme, 
 surpassing the elongate, narrowing tail-plate of B. Kielcemis^ Gurich, of the 
 lower upper Devonian (Cuboides horizon) of Poland. Corda (Prodrom einer 
 Monographie der bohm. Trilobiten, pp. 58, 59, 1847), attempted a further 
 division of the genus on the basis of the simplicity or duplication of the 
 median rib of the pygidium, proposing for such species as show a bifurcation, 
 the name Bicranactis^ and for those in which it is simple, Holomeris. It has 
 long been evident, and is shown in the species in hand, that the duplication 
 of this rib is of such minor significance that it can be regarded only as an 
 individual character and we can not safely infer values from this trait. 
 
 Barrande observed (Systeme Silurien, Vol. I, p. 840) that a division of 
 the species of Bronteus might be founded upon the number of ribs on the 
 pygidium, which are either six, seven or eight on either side of the median 
 rib. By far the greater number of species possess seven ribs, while six such 
 ribs are present only in the earliest species, e, g.^ B. Iwnatus, B. hibernieu.% 
 B. laticauda. Herein B. senescens^ having seven ribs, perpetuates the struc- 
 ture of the normal representatives of the genus. 
 
 The definite time value of the subgenus Tliymnopelti^ has been set forth 
 by Barrois, Kayser, Freeh and other writers. The only representative of this 
 division yet known in American faunas is the species B. tallius^ from the 
 
738 
 
 Report of the State Geologist. 
 
 Tully limestone (Cuboides liorizon) of New York. Though the group is 
 well represented in lower Devonian horizons, there is no record of its per- 
 durance beyond the Cuboides horizon, and we notice that in this late represen- 
 tative of Thysanopeltis the marginal spines are minute and hair-like. Within 
 the limitations of this group we find the glabella passing through variations 
 in dimensions quite similar to those which characterize the genus as a whole. 
 
 Bronteus senescens is devoid of marginal spines and reproduces the char- 
 acters of the normal middle Devonian type. We look upon this species, 
 therefore, as distinctly progressed in the character of its glabella and pygi- 
 dium and as having escaped entanglement with the early Devonian divergence 
 into Thysanopeltis ; a survival, with appropriate time modifications, of the 
 proper expression of the genus. 
 
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