272 PALEONTOLOGY OF ILLINOIS. 



The ventral tube, of which some traces can be seen an inch above 

 the base, appears to have been cylindrical, starting with the two 

 long quadrangular anal plates that rest on the posterior subradial 

 plate, the succeeding plates decreasing upward in size. 



Column at its upper extremity rather large, and composed of ex- 

 tremely short joints, closely ancyhlosed together. 



Position and locality: Upper part of the geode bed, one mile below 

 Keokuk. 



No. 202 of Mr. L. A. Cox's collection. 



POTERIOCRINUS IOWENSIS, Wortheu. 



Poteriocrinus lowensis, WOETHEN. February, 1882. 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 6. 



Body short, about once and a half as wide as high. Basal plates 

 small and hidden by the first columnar joints. Subradials small, 

 slightly protuberant at the center and depressed at the angles. 

 Eadials twice as wide as long, pentagonal, depressed on their lower 

 lateral borders, with a tolerably well defined suture between them 

 and the brachials. 



Brachials two, the first quadrangular, twice as wide as long, the 

 second pentagonal, giving support on their sloping angles to the 

 first divisions of the rays, and slightly protuberant at their upper 

 angles. 



Arms after the first division on the second brachial in two of the 

 rays, the left posterior and right antero -lateral rays divide again 

 on the fifth to the seventh plate, beyond which they are simple as 

 far as they have been preserved. On another ray, which may be 

 the anterior one, the first bifurcation takes place apparently on the 

 fifth brachial, and the second one on the third plate above, as near 

 as can be determined from the crushed condition of this ray. Anal 

 plates unknown. 



Column round, composed of rather thick joints near the body, 

 becoming alternately thinner below. 



This species is related to Pot. (Scaph.) Gibsoni of White, but dif- 

 fers from it in the number and mode of bifurcation of the arms, 

 and also in the form and proportion of the plates composing the 

 body. 



Position and locality: Upper shales of the geode bed, one mile be- 

 low Keokuk, Iowa. 



No. 56 of Mr. L. A. Cox's collection. 



From an oversight this specimen was not figured. 



