15 



truncate below, about as high as wide, and forming by themselves a 

 small pantagonal cup a little more than half as high as wide. 



Subradials about twice as large as the basals, four of them hexag- 

 onal, and two on the posterior side larger than the others and hep- 

 tagonal. Only two of the rays are preserved in the specimen before 

 me, and in one of these, the right posterior one, the radial plate ap- 

 pears to be quadrangular, and rests directly upon the upper margin 

 of the large posterior subradial below. In the leftantero-lateral ray 

 the radial is pentangular, its lower angle fitting in between two of 

 the subradials, as is usually the case in this genus. 



Brachials two, the first quadrangular, and the second pentan- 

 gular, both wider than long, and the last supporting on its 

 sloping sides the first divisions of the rays. The arms in 

 the right posterior ray divide again two or three times, first 

 on the seventh plate, and the outer branch twice more on the 

 eighth and twentieth plate, and the inner division at least once 

 more about the twentieth plate, making as many as ten 

 arms to this ray. The left antero-lateral ray, after its first division 

 on the last brachial plate, gives off branches in each division on the 

 eighth plate, the outer division dividing twice more on the eighth 

 and twenty-second plate, and the inner division once more 

 on the twenty-second plate, which is as far as the arms can be 

 traced. There are at least ten arms each to these two rays, and 

 possibly more. The anterior ray is but partially exposed, and seems 

 to have an axillary plate about the twelfth series above the last 

 brachial. The first anal plate is nearly as large as the smallest sub- 

 radial, and rests between two of them, and a smaller second anal 

 rests upon the first, above which a double series of small plates may 

 be seen that probably form the base of a ventral tube. Column 

 rather stout, the first plates covering the whole diameter of the 

 truncated base. 



This species is closely related to Pot. concinnus, of Meek and 

 Worthen, Geol. Surv. of 111., Vol. 5, page 490, pi. 14, fig. 3, but dif- 

 fers from that in its more elongate body, the very thin plates of 

 which it is composed, as well as in the number and mode of bifurca- 

 tion of the arms. 



Position and locality : Keokuk limestone, Keokuk, Iowa. 



Collection of the author. 



POTERIOCRINUS RICHFIELDENSIS. N. SP. 



Body small, turbinate, length and breadth about equal. Basals 

 moderately large in proportion to the entire body, projecting above 

 the columnar facet so as to form a shallow pentagonal cup. 



Subradials larger than the basals, the two on the posterior side 

 the longest, and hexagonal. 



Eadials wider than long, pentagonal, with a well defined and rather 

 gaping suture between them and the succeeding brachials. In the 

 right posterior ray the brachial is twice as long as wide, pentagonal, 



