ACTINOCEINID^. 607 



vided with sliarp spines from 1|- to 2 mm. in length. Regular interbrachials : 

 1, 2, 2, and 1. The first anal plate supports 2, 3, and 3 plates, and probably 

 two more in the upper regions. Of the ventral disk little is known, except 

 that it was covered by spinous plates. Column preserved only to the extent 

 of a few pieces, which show that the nodal joints near the calyx have sharp, 

 distinctly crenulated edges, and that the intervening joints are narrow and 

 evenly rounded. 



Horizon and Locality. — Same as last. 



Types in the collection of Wachsmuth and Springer. 



RemarJiS. — Distinguished from 0. reticulatus and allied species by the 

 arm formula, and the surface structure of the arms. 



Cactocrinus opusculus (Hail). 

 Plate LYL Figs. 5a, h. 



1860. Actinocrintts opttsculus — Hall; Suppl. Geol. Rep. Iowa, Plate 2, Fig. 6 (witbout description). 



1861. Actimcrinus opusculus — Hall; Boston Journ. Nat. Hist., Vol. VII., p. 264. 

 1881. Ar.tinocrinus opusculus — W. and Sp. ; Revision P,ilfeocr., Part II., p. 144. 

 1893. Whitfield ; Mem. Amer. Mus. Nat. Hist. N. York, p. 9, Figs. 6, 7. 



In form and ornamentation closely resembling C. thetis, but the species is 

 smaller, and differs essentially in the surface structure of the arms. Calyx 

 higher than wide, attaining its greatest width at and above the arm regions ; 

 truncated at the base. The doi'sal cup quite narrow to the top of the dis- 

 tichals, then spreading abruptly, and forming a short rim, somewhat similar 

 to that of Strotocrinus, from which the ventral disk rises almost vertically to 

 one third its height. Surface of plates convex, traversed by narrow ridges, 

 which, passing from the centre of the plates, unite at the edges with those 

 of adjoining plates. 



Basals short, thickened at the outer margins, and indented at the suture 

 lines ; the lower surface deeply excavated ; surface of the plates covered 

 with coarse wrinkles. Eadials and costals almost twice as wide as long, the 

 former somewhat the Larger. Distichals a little smaller than the costals. 

 Palmars quite small ; the two inner ones of each ray supporting two arms ; 

 the two outer but one. Arms thirty ; long, incurving, rounded at the base, 

 but almost perfectly flat above, and somewhat wider, the edges knife-like 

 and distinctly serrated. The arm plates are transversely angular, arranged 

 in parallel rows, each plate marked by a small node placed close to the 

 median suture line. Pinnules similar to those of C. clams, but less closely 



