HEXACRINIDiE. 775 



Eadials once and a half as long as wide, widest across the middle ; the upper 

 faces deeply excavated to more than one half the width of the plates. Costals 

 two, closely anchylosed and very short, their combined length less than their 

 width ; the lower plate, and partly the upper, resting completely within the 

 facet, the distal faces of the upper but slightly angular. Distichals three ; 

 the two lower plates so closely anchylosed that the suture line is frequently 

 obsolete. The costals and distichals, in place of taking the usual outward 

 curve, bend slightly inward, so as to make the width of the specimen directly 

 above the radials less than the width of the cup. Arms twenty (not twelve, 

 as stated by Casseday and Lyon), closely folded at their proximal ends, 

 recurving above the second bifurcation, and the tips hanging downward, 

 exposing the ambulacra. Pinnules long. Anal plate of the same width as 

 the radials, but the lower margin distinctly angular, and the upper concave ; 

 it is followed by numerous small plates forming a small, rounded protuber- 

 ance. Position of the anus almost marginal. Column round. 



Horizon and Locality. — Keokuk limestone ; Crawfordsville, Ind., and 

 Hardin Co., Ky. 



Types in the collection of the late Major Lyon at Jeffersonville, Lid. 



Remarhs. — The specimen which Professor Worthen erroneously figured 

 in the Illinois Geol. Eeport of 1876 under this name has but ten arras, while 

 D.ficiis has twenty. Besides, it differs quite essentially in the form of the 

 calyx. Curiously enough, Worthen described his specimen as having five 

 radials and six costals, evidently supposing, as Casseday and Lyon did, that 

 the anal plate supported two arms. 



This species approaches D. pendens in its tendency to pendent arms; but 

 the latter is larger, the dorsal cup proportionally wider, the base shorter, and 

 bowl-shaped instead of obconical. 



Dichocrinus pentalobus (Cass, and Lton). 

 PMe LXXVIII. Figs. 11a, I, c. 



I860. Cotyhdonocrinus pentalobus — Casseday and Lyon ; Proceed. Amer. Acad, of Arts and Sci., Vol. 



v., p. 2G. 

 1865. (?) Cotyledommnus pentalobus — Shumaed ; Catal. Pnlffioz. Poss. N. Amer., p. 360. 

 1877. Cotyledonoorinus pentalobus — S. A. Miller ; Catal. Amer. Palseoz., Foss., p. 92. 

 1881. (?) Coiyledonocririus pentalobus — Revision Palseocr., Part II., p. 78. 



Calyx elongate; plates thin and without ornamentation. Basals large, 

 forming a sub-ovoid cup with a thickened rim around the lower margin ; 

 bottom but partly occupied by the column. Eadials gradually increasing in 



