184 PALAEONTOLOGY OF ILLINOIS. 



RHODOCRINUS WATERSIANUS (sp. nov.) W. & Sp. 



J 3 !. XVII, Fig. 16. Specimen with arms. Anterior view. 



This species is of the type of R. wortheni Hall, (Geol. of Iowa, 

 1859, Vol. I, Pt. 2, p. 556), which is its nearest congener. It differs 

 from that species in its more concave base, the proportionally 

 smaller size of basals and first radials, and in its globose form . 

 All specimens known to us are light colored. 



Calyx globose, truncate below, and slightly concave. Plates 

 decreasing in size from the basals up. The underbasals are small 

 and concealed by the column. The basals moderately large; their 

 lower end abruptly deflected inward, forming the rim of the basal 

 cavity on which the cup rests. 



First primary radials slightly smaller than the basals. Second 

 and third plates still smaller, decreasing gradually upward. 

 Secondary radials 1x2x5, not more than half the size of the third. 

 They support a series of slightly cuneate arm joints, the fifth of 

 which is axillary. In the type specimen, and the most of those 

 observed, there is but one bifurcation, giving four ultimate arms 

 to the ray, or 20 in all, but we have observed specimens, probably 

 more mature, but otherwise not distinguishable, which have five 

 arms in place of four. 



Arms rounded, slender, tapering gradually, the joints pro- 

 portionally longer and narrower than in R. kirbyi, and the pin- 

 nules stouter. The interradial areas are not depressed, but form 

 an even surface with the other calyx plates. They are composed of 

 about six plates, of which the first is a little more than half the 

 size of the first radials, the succeeding plates decreasing in pro- 

 portion to their rank. Azygous interradius occupied by a median 

 series of three or more comparatively large anal plates, which are 

 hexagonal, and bordered by interradials of about the same size 

 as the corresponding ones in the other areas. They are succeeded 

 by smaller plates extending up to the anal opening, which is small, 

 subcentral, protuberant, and directed upward. 



Ventral side convex, abruptly constricted above the arm bases, 

 with no marked depressions in the interradial spaces. It is com- 

 posed of numerous small, smooth plates. 



