KHODOCRINID^. 225 



to adjoining plates. Eadials nearly as large as the basals, but the ridges less 

 conspicuous. First costals smaller than the second, convex; the second as 

 large as the first. The second distichals support the free arms, which are 

 not preserved. Interradial areas not depressed below the level of adjoining 

 brachials ; composed of the interradial plate, and about nine interbrachials, 

 of which the upper ones are very small. The anal area has one or tw^o 

 additional plates. Ventral disk small ; its diameter scarcely two thirds the 

 width of the dorsal cup at the widest part; composed of numerous very 

 small, highly convex plates. Anus subcentral. Column round. 



Horizon and Locality. — Keokuk group ; Harrison Co., Indiana. 



Bemarhs. — We did not have access to the specimens to illustrate this 

 species, and were obliged to make our description after Miller. 



Rhodocrinus nodulosus Hall. 

 Plate XIII. Fig. 8. 



1862. Modocrinus {AcantJiocrimis) nodulosus — Hall; 15th Rep. N. Y. State Cab. Nat. Hist., p. 126; 



ibid., 1872, Bull. I., Plate la. Fig. 8. 

 1881. RJiodocrinus nodulosus — W. and Sp. ; Revision Palseocr., Part II., p. 212. 



Of medium size. Dorsal cup more rapidly spreading to the top of the 

 second costals than from there to the arm bases ; height and greatest width 

 about equal ; interradial and interdistichal spaces depressed. Plates convex, 

 the surface covered with obscure radiating ridges, and the central portion in 

 most of them produced into a small node. 



Infrabasals small, but plainly visible beyond the column ; the bottom 

 somewhat depressed for the reception of the column. Basals larger than 

 any of the other plates, longer than wide ; the lateral upper faces longer 

 than the lateral lower ; the upper faces rather narrow. Eadials larger than 

 the costals ; three of them pentagonal, the two posterior ones hexagonal ; 

 the costals slightly narrower and shorter. The distichals support the free 

 arms ; fiYe to six of them take part in the calyx, of which the three low^er 

 ones are subquadrangular and twice as wide as long, the two or three suc- 

 ceeding ones cuneate, and slightly interlocking. The free distichals are less 

 convex and shorter than those of the calyx; the succeeding arm plates 

 strictly biserial, and very short. Arms rather stout at the proximal ends, but 

 the size decreases rapidly with each bifurcation. There are two bifurcations 

 in the free arms, and the branches are widely divergent. The large plates 



29 



