INVERTEBRATES. 317 



small, and might be easily overlooked in imperfect specimens, taken in connec- 

 tion with the fact that the lowest range of pieces represented in Prof, de Ko- 

 ninck'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 Prof, de 

 Koninck's specimen. If so, then the identity of our Crinoid with his Indian 

 type would be complete. Until this question can be satisfactorily settled, how- 

 ever, we have concluded to retain our name Erisocrinus for the American type. 

 Should they prove identical, however, of course Prof, de Koninck's name will 

 have to take precedence, since it has priority of date. 



So far as we know, this genus is confined to the Carboniferous rocks. Mr. 

 Marcou thought its close analogy to Encrinus indicated that certain Coal Meas- 

 ure rocks in which he found it in Kansas, belong to the part of the Permian 

 series he calls "Dyas." He was, however, at that time, not aware of the fact, 

 that the same species he found in Kansas, and two others of the same genus, 

 occur in the Coal Measures of Illinois, curiously enough at the same time re- 

 ferred by him to the Subcarboniferous. 



Erisocrinus ttpus, M. and W. 



Erisocrinus typus, Meek and Worthen, March, 1865. Am. Jour. Sci., vol. xxix, p. 1Y4. 

 Philocrinus pelvis, Meek and Worthen, May, 1865. lb., p. 350. 



Erisocrinus nebrascensis, Meek and Worthen. March, 1865. Am. Jour. Sci., vol. xxix, 

 page 174. 



Body below the summit of the radial pieces basin-shaped, 



rounded below, and obscurely subpentagonal in outline as seen 



from above or below; composed of thick, 



smooth, slightly convex plates. Basal 



pieces small, about half hidden by the 



, , ; w\\ column, sometimes sunken, and all penta- 



\Hf^( r ~\\ \l/ gonal in form ; subradials six or seven 



y — vO, — x times as large as the portion of each basal 



\^) v?0/ pi ece n °t hid by the column, all equally 



\ — / v_ — / hexagonal ; first radial pieces four or five 



Erisocrinus typus. — (Nat. size.) . - i -i • i • -i .li 



Diagram showing the form and times as large as the subradials, wider than 



arrangement of the basal, subra- 



dial, and erst and second, radial long, and all equallv pentagonal, support- 

 pieces. (The latter with mlddlj D ' a •/ a ° ' rr 



angle too prominent.) j n g on thgjj. broadly truncated upper edges 



