This species is related to Pot. {Scaph.) Gihsoni of White, but dif- 

 fers froni 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 

 below Keokuk, Iowa. 

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



POTEEIOCEINUS HAMILTONENSIS N. SP. 



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 

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

 Eadials, 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 theradials, and four of them sharply angular above for the 

 support of die 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 alto- 

 gether for this species. Four or five anal plates can be seen ar- 

 ranged as usual in this genus. Arms composed of short quadrangu- 

 lar 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.) 

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

 rangement of the arms. 



Position and locality: Upper part of the Keokuk limestone, 

 Hamilton, 111. 



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



POTERIOCRINUS ORESTES N. SP. 



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 

 below, Eadials about twice as large as the smaller subradials, four 

 of them pentagonal, and one on the right posterior side heptagonal, 

 counting three angles below. 



Brachials, five to the anterior ray, the first one of which is as wide 

 below as the fii'st radial, but constricted above to correspond with 



