NATURAL SCIENCES OF PHILADELPHIA. 71 



ever, we thought it desirable to change the specific name of our species typ^l,s, 

 it not being the type of the genus I'hilocrinus. 



We were led to regard our species as not being generally distinct from 

 Philocrinus, because they agree exactly in all their known generic characters, 

 unless the lower range of pieces shown in the figure of Fliilocrinm reallj'' are 

 the basal pieces, which would make that genus without subradial pieces. 

 As the typical specimen, however, seems, from the figure, to be a little defec- 

 tive at the lower extremity, and the lowest range of j)ieces represented, if 

 really prolonged to the bottom of the body, would have to present a very 

 remarkably elongate cuneiform outline, we were strongly impressed with the 

 probability of there being another smaller series of true basal pieces below 

 the lowest range represented (but not visible in consequence of the con- 

 dition of the specimen), especially as these forms appear to agree so nearly 

 in other respects. If so, there would be no generic differences between 

 Philocrinus and Erisocrinus, and the American species would have to stand 

 under the former name. If Philocrinus, however, really has no subradial 

 pieces, then, of course, Erisocrinus must be an entirely distinct genus. Until 

 all doubts on this point, however, can be removed, we finally concluded to 

 retain our name Erisocrinus. 



The close similarity of the body of some species of this genus, and that 

 of another allied form, found in the upper members of the Coal-Measures of 

 Nebraska, to the corresponding parts of the genus Encrinus, and tlieir wide 

 difference from all the then known Lower Carboniferous Crinoids of America, 

 have been appealed to as facts sustaining an opinion, maintained by some, that 

 these Nebraska beds belong to the age of the Permian of Europe, instead of 

 to the Coal Measures. The fact, however, that we now have the species of 

 this genus described in this paper, from the lower part of the lower Carboni- 

 ferous or Mountain Limestone at Burlington, ought, we should think, to be 

 sufficient evidence that no such conclusions can be properly based on this 

 type of fossils. 



Erisocrinus antiquus, M. and W. 



Body small, much depressed, somewhat basin shaped, or very rapidly ex- 

 panding from the base to the summit of the first radial pieces, at the connec- 

 tions of which it is very faintly sinuous around the margins, as seen from be- 

 low. Base small, subpentagonal, almost entirely covered by the round, flat 

 facet for the attachment of the column ; basal pieces exposing very small pen- 

 tagonal surfaces, three or four times as wide as long. Subradial pieces each 

 about one-half to two-thirds as large as the whole base, all uniformly pentag- 

 onal (there being no visible angle at the middle of the base), and with the up- 

 per sloping sides each about twice the length of the lateral margins. First 

 radial pieces about twice as large as the subradials, half as long as wide, and 

 all equally pentagonal, with the lateral and inferior sloping edges of nearly 

 equal length, and the straight, upper truncated side equaling the entire breadth ; 

 articulating upper edge very thick, deeply notched at the middle on the inner 

 edge, and provided with the usual transverse ridge and furrows. Second 

 radials as wide as the first, and about three-fourths as long as wide, angular 

 in the middle on the dorsal side, and constricted on each lateral margin ; pen- 

 tagonal in form, and supporting on their superior sloping sides the first arm 

 pieces, which are quadrangular, slightly constricted on each side, and a little 

 wider than long; arms beyond these simple (as far as they can be traced in 

 the specimen), two to each ray, or ten in the whole series, and composed of 

 somewhat shorter quadrangular pieces, provided with a well defined ambula- 

 cral furrow within. Surface merely finely granular. 



Height of body to the top of the first radials, 0-12 in.; breadth, 0-23 in. 



This little species will be readily distinguished from those already known 

 from the coal measures, by its much more depressed, rapidly expanding body, 

 as well as by its proportionally longer and constricted second radial pieces. 



1869.] 



