24 



brachials, and one of them gives off a second branch on the eighth 

 plate, while the others are not preserved beyond the second division 

 above the brachials. The arms are composed of short wide plates, 

 the two first above the brachials being about twice as long as the 

 succeeding ones, and all a little wedge shaped. The arms are only 

 about half as wide above the second bifurcation as below. Anal 

 plates unknown. 



Column round, composed near the base of thick and thinner plates 

 alternately arranged. 



This species is related to Pot. (Scaph.) Ilamlolphensis Geol. Surv. 

 of 111., Vol. 5, page 551, but differs in its wider and more nearly 

 parallel arm plates, as well as in the bifurcation of the arms. 



Position and locality : Chester limestone, Pope county, 111. 



Illinois State collection. 



POTERIOCRINUS OKAWENSIS. N. SP. 



Body of medium size, wider than high to the top of the radial 

 series, composed of smooth slightly convex plates. 



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 on 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 plate, 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.) liandolphensis horn the 

 same horizon, l)ut 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. 



Illinois State collection. 



POTERIOCRINUS VENUSTUS. N. SP. 



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. 



