842 



PROCEEDINGS OP THE ACADEMY OP 



agreeing with Ci/athocrinus proper in the thinness of its body plates, in the na- 

 ture of the bifurcations of its arms, and apparently in the general structure of 

 its body, excepting that it has no anal plate, the first radials being large, wide, 

 and in contact all around, so as to leave no spaces for anal or interradial 

 pieces. The succeeding radials after the first are comparatively small, and 

 number from three to four (so far as yet known) to each ray, the first always 

 resting in rounded sinuses in the upper edge of the large first i-adials, much as 

 in Cyathocrinus, excepting that these free radials are very short, more as we see 

 in Barycrinus. They differ, however, from those of both Ci/athocrinus and Ba- 

 rya-inus, in each having its lower edge along the outer side of the arms pro- 

 duced downward, into a corresponding sinus in tlie upper outer edge of each 

 succeeding piece below, so as to present much the appearance seen in the arms 

 of Taxocrinus, Onyc/wcrinus and Forbesiocrimis, excepting that the produced part 

 does not seem to be separate patelliform pieces, but merely the downward 

 produced lower outer edge of each arm-piece itself. 



None of the specimens yet found show the number of basal pieces, but we can 

 see that its body is composed of small basals, witli five well-developed subra- 

 dials of uniform shape, and five large first radials. This structure of the body, 

 it will be seen, is exactly that of Erisocrinus, — that is if the base is composed 

 of five pieces, which is very probable. The whole structure and aspect of the 

 parts above, however, is entirely different in these groups, since in Krisocrinas 

 there are alwaj-s but two primary radial pieces to each ray, while the second 

 radials are as large as the first, and instead of merely resting in small sinuses 

 in the upper part of the latter, the two articulate together by straight edges 

 across their entire breadth, the articulating edges being always provided with 

 a crenated transverse ridge and furrows. The arms of Ensocrhius are also 

 much stouter, and present none of tlie characters of the type under considera- 

 tion, while all of its body and arm pieces also differ in being very thick. 



It is an interesting fact that the column of the genus here described, as well 

 as its arms, present a striking similarity to that of Taxocrinus and allied groups, 

 being round, and composed near the body of exceedingly thin pieces, connect- 

 ing by crenate surfaces, and provided with a comparatively small central 

 canal. Notwithstanding these points of resemblance, however, to Taxocrinus, 

 it is evident that this group is more nearly allied to Cyathocrinus. If it has, as 

 seems to be the case, five basal pieces, the formula of the genus would be as 

 follows : 



Basal pieces 5 ; subradials 5, all of the same form ; radials 4 to 5 X 5, the 

 first being large and forming the larger part of the body, the others small and 

 free ; anals ; interradials ; arms bifurcating, and resembling those of Taxo- 

 crinus. 



Some five or six specimens of this type show that the absence of anal pieces 

 is not an abnormal, but a constant character. 



NiPTEROCRiNus Wachsmuthi, M. and W. 

 Body rather deeply basin-shaped, or a little more than twice as wide 

 as high, rounding under from the top of the first radials to the column. 

 Base small, fiat, and nearly hidden by the column. Subradial pieces 

 of moderate size, somewhat wider than long, and all pentagonal, there 

 being no visible angle at the middle of the under side of any of tlicni. First 

 radials comparatively very large, or about three times the size of the subradi- 

 als, twice as wide as higli. and all alike pentagonal ; while each is provided 

 with a rather deep rounded sinus above, equaling about one-third of its breadth, 

 for the reception of the succeeding radials, on each side of which its upper 

 margin is nearly straight, horizontal, and not incurved. Second radials so short 

 as scarcely to fill the sinus in the upper side of the first, and owing to the con- 

 cave outline above, often presenting a narrow transversely crescentic form. 

 Third and fourth radials (where there are five) very short, or several times as 

 wide as long, and usually somewhat arcuate inversely. Last (fourth or fifth) 



[Dec. 



