HEXACEINlDiE. 801 



Lyon's Pterotocrinus rugosus is probably also identical with this species, 

 but as the type specimen is fragmentary and badly crushed, no critical com- 

 parison is possible, and we think it advisable to accept Wetherby's name. 



Pterotocrinus acutus, var. bifureatus (Wetheeby). 

 Plate LXXIX. Figs. 9a, b. 



1879. Wetheket ; Joura. Cincin. Soc. Nat. Hist. (October No.), Plate 11, Figs, la, b, c. 

 18S1. W. and Sp. ; Revisiou Palffiocr., Part II., p. 91 (Proceed. Acad. Nat. Sci. Phila., p. 265). 



This variety agrees in the general arrangement of its plates with P. acu- 

 tus, but differs from it in the form of the dorsal cup and the form of the 

 appendages. The cup is higher and more conical ; the basals proportion- 

 ally deeper, their lower faces distinctly excavated, and sharply edged around 

 the margin. The appendages are long and extremely heavy throughout; 

 they bifurcate widely, in such a way that the divisions from adjoining rays 

 meet at their ends and sometimes overlap each other. Column small, filling 

 scarcely one half of the basal cavity. 



Horizon and Locality. — Kaskaskia group; Sloans Valley, Pulaski Co., Ky. 



Type in the collection of Prof. A. G. Wetherby. 



Pterotocrinus CraSSUS Meek and Wokthbn. 

 Plate LXXIX. Fig. 8. 



1860. Dichocrinus (Pterotocrimis) crassus — Meek audWoKTHEN; Proceed. Acad. Nat. Sci. Pliila., p. 382. 

 1860. Pterotocrinus crassus — Meek and Worthen; Geol. Rep. Illinois, "Vol. II., p. 290, Plate 23, 



Figs. 2ff, b. 

 ISSl. Pterotocrinus crassus — W". and Sp. ; Revision Palffiocr., Part II., p. 91, 



This species has its closest affinities with P. pyramidalis Lyon and Cass., 

 but is somewhat larger, the basal cup deeper, the arms longer and heavier. 

 Dorsal cup basin-shaped, more than twice as wide as high, very broad at the 

 base, the sides less .spreading than in any of the preceding species, and some- 

 what constricted at the basi-radial suture. 



Basals very large, forming a rounded shallow cup, distinctly concave 

 below, and widening gradually from the rounded lower margin to the con= 

 stricted upper face. Radials a little convex, broader than long, considerably 

 wider above than below ; their upper faces slightly concave, supporting the 

 costals, distichals, and the outer palmars of the first row. Anal jjlate sub- 

 quadrangular, contracted above, the upper end inflected. Costals very small, 



101 



