734 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Basals short, the sutures visible. Eadials not quite as wide as long, hex- 

 angular ; the upper face for the reception of the costaJs and distichals a little 

 concave ; the sloping upper faces forming a deep notch for the reception of 

 a large interbrachial plate. Costals moderately large for the genus, trigonal, 

 wider than high. Distichals a little larger than the costals ; pentagonal and 

 axillary. They rest with their lower faces upon the radials, and with one 

 of their lateral ones against each other, with the opposite one against a large 

 interbrachial, which rises to the top of the first arm plate, incorporating this 

 with the calyx. Arms four to the ray ; the five or six proximal arm plates 

 wedge-form, and arranged in a single series; the succeeding ones gradually 

 changing from cuneate to pentangular, and disposed in two rows ; the sur- 

 face of the plates somewhat convex and thickened in the direction of the 

 pinnules. Pinnules heavy, composed of long joints, thickened at the ex- 

 tremities, and slightly constricted along the middle. The proximal pinnule 

 of the two inner arms of the ray is given off from the inner side, that of the 

 two outer arms from the outer side of the ray. Structure of ventral disk 

 unknown. 



Horizon and LocalUy. — Lower Helderberg group ; Schoharie, New York. 



(?) Marsupiocrinus prsematurus (Hall and Whitf.). 

 Plate LXXII. Figs. 11a, h. 



1875. Platijcrinus pramatiirus — Hall and Whitfield: Geol Surv. Ohio, Vol. II,, p. 124, Plate 6, 



rigs. 3 to 6. 

 1885. Marsupiocrinus pramaiurtts — W. and Sp. ; Revision, Part III., p. 115 (Proceed. Acad. Nat. Sci. 



PliUa., p. 337). 



Of medium size. Dorsal cup not as high as wide, stronglj^ quinquelobate 

 in a dorsal aspect, owing to the thickened, tumid character of the radials, 

 which form the widest part of the calyx ; the sides of the cup rapidly 

 contracting to both ends. Plates heavy and strongly convex ; the sm-face 

 smooth. 



Basals moderately large, constituting only a small proportion of the 

 height of the dorsal cup ; their centres tumid, and projecting downward in 

 the form of three strong, rounded nodes ; the inner portion of the plates, 

 which forms the columnar attachment, deeply concave. The interbasal sutures 

 distinctly grooved. Radials large, more than once and a half as wide as long, 

 the facet for the reception of the costals and distichals somewhat indented, 



