NATURAL SCIENCES OF PHILADELPHIA. 149 



Surface smooth, or only with traces of flue granules. Sutures a little con- 

 cave. Column comparatively strong and rounded near the base, where it is 

 composed of short joints, and marked with obscure, regular longitudinal striae. 



Height of body on the anal side, 0.28 inch; do. on the opposite side, 0.22 

 inch ; greatest breadth above (allowing for a slight accidental compression) 

 about 0.38 inch ; breadth of free arms at their connection with the body, 0.08 

 inch ; breadth of column at its connection with the base, 0.16 inch. 



This species presents points of analogy both to Heterocrinus, Hall, and Hybo- 

 crinus, Billings, and yet seems to differ from both to such an extent, that if 

 we could be sure some of its peculiarities are not abnormal in our specimen, 

 we would be inclined to view it as the type of a new genus. As we have seen 

 but the one specimen, however, which is not complete in all its parts, we 

 have concluded to place it, for the present at least, as the type of a subgenus 

 under Heterocrinus. It differs from the typical species of that genus in having 

 the column round instead of pentagonal, and in having only the first primary 

 radial pieces in three of the rays, and two in each of the others, included as a 

 part of the walls of the body ; while its preceding primary radials are very 

 narrow, and form small, rounded, distantly separated arms, instead of being 

 nearly as wide as those soldered in the walls of the cup. Another peculiarity 

 is the strongly incurved superior lateral angles of the large radial pieces around 

 the margin of the cup between the arms. 



In the rather unsymmetrical form of the body, the slender proportions of 

 the free arms, and its general aspect, it resembles Hybocrinus, from which it 

 differs in having but one anal piece connected with the walls of the cup, and 

 in having two of the rays and two of the primary pieces included in the wall, 

 while its free arms bifurcate twice or oftener, instead of being simple from 

 their origin. 



Locality and position. Cincinnati, Ohio. Cincinnati Group of Lower Si- 

 lurian. 



Genus ERISOCRINUS, M. & W. 



Erisocrinus, M. & W., Am. Jour. Sci. xxix. p. 174, March, 1865. 

 Philocrinus, M. & W., ib., May, 1865 ; not Koninck, 1863. 



Generic formula. 



Basal pieces, 5 \ 



Subradials, 5 > united to form the walls of the body. 



Radials, 2 X 5 } 



Anals and interradials, 0. 

 Soon after publishing the description of this genus, we were led by its simi- 

 larity to a genus described by Prof. Koninck, from the Carboniferous rocks of 

 India, to believe it identical, and ranged our species under that name. Later 

 comparisons have caused us, however, to doubt the correctness of this con- 

 clusion. If there is no mistake in regard to Philocrinus being without a range 

 of subradial pieces, then the two types would be clearly distinct. The fact, 

 however, that the basal pieces in Erisocrinus are small, and might be easily 

 overlooked in imperfect specimens, taken in connection with the fact that the 

 lowest range of pieces represented in Prof. Koninck's figure, if true basals, 

 would have to present a singularly elongated cuneiform outline, leads us to 

 suspect there may be another range of small true basal pieces below them, 

 but not visible, from some imperfection in the speeimen in Prof. Koninck's 

 type. If so, then the identity of our Crinoid with our Indian type would be 

 complete. Until this question can be satisfactorily settled, however, we have 

 concluded to retain our name Erisocrinus for the American type. Should 

 they prove identical, however, of course Prof. Koninck's name will have to 

 take precedence, since it has priority of date. 



1865.] 



