INVERTEBRATES. 273 



POTERIOCRINUS HAMILTONENSIS, Worthen. 



PI. XXVII, Fig. 9. 



Poteriocrinus Hamiltonensis, WOETHEN, Feb. 1882. 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 7. 



Body short, forming a low, shallow cup about twice as wide as 

 high. Base concave, the basal plates being hidden by the first col- 

 umnar joints. Subradials of nearly uniform size, four hexagonal and 

 one heptagonal, all curving below into the basal concavity. Radials, 

 four of them nearly twice as wide as long, pentagonal, the one on 

 the anterior side smaller, and all indented at their lower angles to 

 correspond with the similar indentations of the upper angles of the 

 subradials. A somewhat gaping suture exists between the radial and 

 brachial series. Brachials, one to each ray, longer than the radials, 

 and four of them sharply angular above for the support of the arms. 

 On the anterior ray the brachial is constricted above to about one- 

 half its width below, and on its upper truncated margin supports 

 the plates of a single arm, making nine arms altogether for this 

 species. Four or five anal plates can be seen arranged as usual in 

 this genus. Arms composed of short quadrangular plates, that give 

 off strong pinnules, the joints of which are twice or more as long 

 as wide. Column, unknown. 



This species is nearly related to the little form to which we have 

 given the name P. penicilliformis, but differs from that in its more 

 broadly cup-shaped body, shorter brachials and arm-plates, and also 

 in the pit-like depressions at the angles of the body-plates. The 

 body alone could not be easily distinguished from Pot. (Scaph.) unicvs 

 of Hall, while it is entirely unlike that in the number and arrange- 

 ment of the arms. 



Geological position and locality: Upper part of the Keokuk lime- 

 stone, Hamilton, Illinois. 

 No. 176, Mr. L. A. Cox's collection. 



POTERIOCRINUS ORESTES, Worthen. 



PL XXVII, Fig. 3. 



Poteriocrinus Orestes, WOBTHEN. Feb. 1882. 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 7. 



Body depressed, cup-shaped, about twice as wide as high. Base 

 concave, basals small and concealed under the first columnar joints. 

 Subradials as wide or a little wider than high, three hexagonal and 

 two on the posterior side heptagonal, all curving into the cavity 



lo 



