INVEETEBRATES. 297 



Base truncated, the basal plates extending above and beyond the 

 columnar facet, so as to form a low pentagonal cup. Subradials 

 about as long as wide, three of them hexagonal, and two on the pos- 

 terior side larger than the others and heptagonal. 



Eadials nearly or quite twice as wide as long, pentagonal, and 

 truncated squarely across the entire length of their upper margins 

 for the reception of the brachial plates. 



Brachials one to the ray on the two rays visible, about the same 

 size as the radials, supporting 011 their upper sloping sides the first 

 divisions of the rays. 



The arms are composed throughout of short, wide, quadrangular 

 plates, and after the first division on the radials, divide again in the 

 left posterior ray on the ninth or tenth plates and on the right 

 antero-lateral, on the seventh and eleventh plate, beyond which 

 they are simple as far as can be seen, making four arms to each 

 of these rays. 



The anal side of the specimen is distorted, but six small anal plates 

 are partially exposed, arranged in two rows. 



This species is related to Pot. (Scaph.) Randolphensis from the 

 same horizon, but differs essentially from that, in the mode of bifur- 

 cation, and the wide, short plates of the arms. 



Position and locality: Chester limestone, bluffs of the Okaw river 

 above Chester, Randolph county, 111. 



No. 2,441, Illinois State collection. 



POTERIOCEINUS VENUSTUS, Worthen. 



PI. XXIX. Fig. 13. 



Poteriocrinus vvnustus, WOKTHEN, February, 1882. 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 24. 



Body small, obconical, gradually swelling from the base to the top 

 of the radial plates, where it is about once and a half as wide as 

 long. 



Basals extending about half their length above the first columnar 

 joints, forming a low pentagonal cup. 



Subradials nearly equal in size, three hexagonal, and two on the 

 posterior side heptagonal. 



Radials four, a little wider than long, the right posterior one 

 rather narrower than the others, and all pentagonal. 



