INVERTEBRATES. 91 



reception of the succeeding- plates. Brachials one each to the 

 posterior and antero-lateral rays, while the anterior ray has 

 four. The first brachial on this ra3' is about as long' as wide, 

 quadrangular, and like the corresponding plate on the other 

 rays, is constricted, rounded on the outer surface, and succeeded 

 by two short plates, the upper one giving- support to a nodose 

 axillary plate on which the first division of the ray takes place. 

 In this ray the outer division bifurcates a.gain on the tenth 

 plate, but the inner continues single as far as it is preserved. 

 The right antero-lateral ray bifurcates the second time on the 

 sixth plate, and both divisions again on the sixth to the 

 eleventh plate above, giving eight divisions to this ray. The 

 left antero-lateral ray has its first bifurcation on the sixth plate, 

 the inner division dividing again on the eighth plate, the outer 

 one continuing single as far as it can be seen, giving but six 

 divisions to this ray. The poster o-lateral rays bifurcate in the 

 same manner as the left antero-lateral ray, giving six divisions 

 to each of these rays, and twenty-nine to the entire animal. 

 The rays are composed of rather short, wedge-shaped pieces, that 

 decrease very gradually in width towards their extremities. 



Five anal plates are visible, the two lower ones resting appar- 

 ently on one of the basals, an appearance that is probably due 

 to the partial displacement of the body plates by pressure. 



Column round or slightly pentagonal, and composed of alter- 

 nate thin and thicker joints. 



This crinoid has the general form of Zeacrinus, as defined by 

 \Vachsmuth and Springer, the only difference observable being 

 the mode of bifurcation of the rays. 



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



Collector, A. H. Worthen. 



No. 2492 of the Illinois State Museum. 



POTERKH KINTS MAMM.KFOHMIS. (sp. UOV.) 



Body small, obconic or mamilhpform below the base of the 

 arms and squarely truncated below where it is united with the 

 column. Under-basals long and narrow, slightly angular at their 

 summits, forming a little cup about once and a half as wide as 

 high. Basals scarcely as long as the under-basals, but wider, 

 probably hexagonal and heptagonal. Primary radials two, the 



