NATURAL SCIENCES OP PHILADELPHIA. 137 



Generic formula. 



Basal plates, 5 ? 



Subradial plates, 5 ; four hexagonal and one pentagonal. 



Radial plates, 2X5. 



Anal plate, 1. 



Interradial plates, none. 



Arms, 10, bifurcating. 

 The crinoid upon which we propose to found this genus, has much the ap- 

 pearance of an Ichthyocrinus, with which genus it seems to agree, excepting in 

 having true subradial plates, and but two, instead of three primary radial 

 plates in each ray ; also in the possession of a distinct anal plate. 



Notwithstanding its general similarity to Ichthyocrinus, its structure is more 

 nearly like that of Cyathocrinus, from which it differs mainly in having only 

 two, instead of three primary radial pieces in each ray, and much broader and 

 flatter arms, which connect laterally as in Ichthyocrinus, so as to leave no in- 

 terradial spaces. 



Bursacrinus Wachsmuthi. Body below the summit of the first radial plates 

 rather broad turbinate, or rapidly expanding from below. Base unknown. 

 Subradial plates of moderate size, a little wider than long, and all hexagonal, 

 excepting one on the anal side, which is larger than the others, and hept- 

 agonal in form ; the angles at the middle of the under side of each being less 

 salient than that above. First radial plates about one-third larger than the 

 subradials, near twice as wide as high, and all pentagonal, the upper side 

 being transversely truncated. Second radial pieces of the same size and form 

 as the first, but inverted so as to bring the truncated side below ; supporting 

 on their superior sloping sides the first divisions of the arms, which are broad, 

 flat, and connected laterally with each other all around. Anal piece rather 

 small, longer than wide, heptagonal, the angle at the middle of the summit 

 being more salient than the others ; supported upon the short truncated 

 upper side of one of the subradials, and connecting on each side with the first 

 and second radial plates, and the first of the broad secondary radial or arm 

 pieces above. 



After the first division on the second radials, the arms bifurcate again on 

 the sixth or eighth piece, above which one is seen to bifurcate again on the 

 twelfth piece, which is as far as they can be traced in the only specimen seen, 

 though they seem to be long and probably bifurcate once or oftener above 



Between the divisions on the second radial pieces, and the next bifurcation 

 above, they are very wide, flat, and composed of short, slightly wedge- formed 

 pieces, which are squarely truncated on each side. The next divisions above 

 these are a little more than half as wide, and composed of a single series of 

 pieces bearing near the same proportions of length and breadth as those below. 

 The surface is finely granulose, though there are no traces of nodes, costse, or 

 other prominences on any of the plates. The sutures are merely linear, and> 

 not impressed. 



We take pleasure in dedicating this interesting species, (the type of a new 

 genus,) to Mr. Charles Wachsmuth, of Burlington, Iowa, who discovered 

 the only specimen we have seen. 



Position and locality. Burlington Limestone. Burlington, Iowa. 



Genus POTERIOCRINUS, Miller, 1821. 



Poteriocrinus ? enormis. Body small, irregularly cup-shaped ; sides some- 

 what convex, expanding from the base ; breadth greater than the height. 

 Base small, spreading from the column, above which the plates are seen pre- 

 senting small pentagonal faces. Subradial plates comparatively large, un- 

 equal, hexagonal in form, excepting one on the anal side, which is much 

 larger than the others, and sub-heptagonal in outline. First radial plates 



1861.] 10 



