276 PALAEONTOLOGY OF ILLINOIS. 



POTERIOCRINUS PENiciLLiFORMis, Worthen. 



PI. XXVIII, Fig. 9. 



Poteriocrinus penicillif>.rmis, WOETHEN, February, 1882. 



Bulletin No. 1. of the Illinois State Museum of Natural History, p. 8. 



Body small, forming below the summit of the radial plates a low 

 cup, about twice as wide as high. Basals, and the lower angle of 

 the subradials, concealed under the first columnar joints. 



Subradials about as long as wide, except the one on the posterior 

 side, which is a little longer than the others. Kadials about twice 

 as large as the basals, wider than long, and truncated squarely 

 across their upper margins for the reception of the brachials. 

 Brachials twice as long as wide, four of them pentagonal, constricted 

 in the middle, and supporting two arms which continue simple to 

 their extremities. The anterior ray has a long quadrangular brachial 

 plate supporting a single arm, making nine arms altogether for this 

 species. 



Arms composed of rounded joints that are generally longer than 

 wide, but slightly wedge-shaped, giving off strong pinnules from 

 their longest sides. 



Column slightly larger at its junction with the body than below, 

 composed of alternately thicker and thinner joints. 



First anal plate longer than wide, pentagonal, and rests partly 

 between two of the subradials and under the right posterior radial. 

 Above this a double series of small anal plates can be seen, the 

 first of which rests on top of the left posterior subradial, and the 

 second on the first anal. 



This little crinoid is related to that described by Meek and Wor- 

 then in the second volume of the Geol. Survey of Illinois, p. 238, 

 pi. 17, fig. 6, under the name of Scaphiocrinus decadactylus, but differs 

 from it in the proportions of the body plates, and especially in its 

 brachials and arm plates. 



Position and locality: Upper part of the Keokuk limestone, Hamil- 

 ton, Illinois. 



No. 269 of Mr. L. A. Cox's collection. 



