16 Cincinnati Society of Ndtvral Jlistov}/. 



arched over, near the beak, b}^ a small pseudo-detidium. Interior show- 

 ing cardinal teeth to be small; muscular impressions undefined. 



Dorsal valve concave, with deepest concavity near the middle, and 

 following- so nearl}^ the curve of the ventral valve as to leave but a very 

 thin visceral cavity within; beak not distinct from the cardinal margin: 

 area very narrow, and ranging at right angles to the plane of the valves- 

 Interior of this valve not observed. Surface of both valves marked by 

 distinct, sub-angular, radiating plications, some of which bifurcate once 

 or twice, at about the middle of their length. Near the free margins 

 the strife number from eighteen to twenty-five. 



Length of a mature specimen, 0.13 inch; breadth, 0.25 inch ; convexi- 

 ty, 0.06 inch. 



From young specimens ofX. (.'') serciea, Sowerb}', this species is dis- 

 tinguished by having comparatively strong plications instead of the 

 exceedingly fine strife of that species; and in having a greater convex- 

 ity. 



Formation and locality: in the Utica shale, associated with Trinrthrus 

 becki, at Cincinnati, O., and Covington, Ivy. 



Heterocrinus geniculatus, n. sp. (Plate VII., figs. 13, ]3o, 13b, 13c.) 



[Ety. — Geniculatus, jointed, geniculated.] 



Body small, obconic, and slightly longer than wide. Basal pieces 

 })entagonal, iabout as wide as high, or a little wider. First radial plates in 

 four of the rays, convex, about as wide as high, and pentagonal in form ; 

 each supporting on its upper side a considerably larger sized second 

 radial, that is quadrangular in outline, with a length and width about 

 equal; in the right posterior ray. this piece is slightly truncated for its 

 articulation with the first plate of the azygos or anal series; third radial 

 in these ra3s a little smaller than the second, wider than long, and con- 

 tracted at the upper end to about two thirds of the length of the lower 

 side; these support a somewhat smaller, regularly pentagonal fourth ra 

 dial, the two lateral edges of which are not parallel, but converge toward 

 the inferior end ; this is an axillary piece, and bears two arms on its upper 

 sloping faces. First radial in the fifth or right lateral ray compara- 

 tively large, obscurely pentagonal in outline, and longer than wide, 

 having a length that is nearly equal to the combined height of the first 

 and second radial pieces in the other rays; this piece supports a sec- 

 ond radial which in form and size is tlie same as the third radial in 

 the other rays; above this is an axillary piece, which bears two arms 

 on its superior sloping sides, and in form and size is similar to the ax- 

 illary' or fourth radial plates of the other series of primary radials. 

 Arms, from their origin on the third and fourth radials, simple through- 



