9 



quadrangular plates, resembling closely the arms of Woodocrinus 

 and Bursacrinus. In two of the rays which are partly preserved in 

 the specimen before me, a second bifurcation takes place on the 

 fourth plate above the brachials, beyond which the arm structure is 

 unknown. The first arm-plates in the two posterior rays are about 

 twice as long as the succeeding ones. 



Three anal plates are visible ; the first one is larger than the 

 others, and rests between the upper angles of the two posterior sub- 

 radials. The second rests on top of the left posterior subradial, and 

 the third, which is smaller than either of the others, rests upon the 

 first, and above this the lower margins of two or more succeeding 

 plates can be seen. 



Column stout, covering the entire width of the base, and com- 

 posed at hrst of nearly equal joints that decrease in diameter below, 

 and pass into a series of alternately thick and thinner joints as the 

 distance from the base increases. 



Position and locality: Upper part of the Keokuk limestone, 

 Hamilton, 111. 



No. 401 of Mr. L. A. Cox's collection. 



POTERIOCRINUS PENICILLIFOEMIS. N. SP. 



Body small, forming below the summit of the radial plates a low 

 cup, about twice as wide as high. Basals, and the lower angle of 

 the subradials, concealed under the first columnar joints. 



Subradials about as long as wide, except the one on the posterior 

 side, which is a little longer than the others. Eadials about twice 

 as large as the basals, wider than long, and truncated squarely 

 across their upper margins for the reception of the brachials. 

 Brachials twice as long as wide, four of them pentagonal, con- 

 stricted in the middle, and supporting two arms which continue 

 simple to their extremities. The anterior ray has a long quadran- 

 gular brachial plate supporting a single arm, making nine arms alto- 

 gether for this species. 



Arms composed of rounded joints that are generally longer than 

 wide, but slightly wedge-shaped, giving off strong pinnules from 

 their longest sides. 



Column slightly larger at its junction with the body than below, 

 composed of alternately thicker and thinner joints. 



First anal plate longer than wide, pentagonal, and rests partly 

 between two of the subradials and under the right posterior radial. 

 Above this a double series of small anal plates can be seen, the first 

 of which rests on top of the left posterior subradial, and the second 

 on the first anal. 



This little crinoid is related to that described by Meek and Worthen 

 in the second volume of the Geol. Survey of Illinois, p. 238, pi. 17, 

 fig. 6, under the name of Scaphiocrinus decadatylus, but differs from 

 it in the proportions of the body plates, and especially in its brach- 

 ials and arm plates. 



—2 



