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734 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Basals short, the sutures visible. Radials not quite as wide as long, hex- 
angular; the upper face for the reception of the costals 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 Locality. — Lower Helderberg group; Schoharie, New York. 
(?) Marsupiocrinus prematurus (Hatz and Wurrr.). 
Plate LX XIL Figs. 11a, b. 
1875. Platycrinus prematurus — Hatt and Wuarrrietp: Geol. Surv. Ohio, Vol. II., p. 124, Plate 6, 
Figs. 3 to 6. 
1885. Marsupiocrinus prematurus —W.and Sr.; Revision, Part IIL, p. 115 (Proceed, Acad. Nat. Sci. 
Phila., p. 337). 
Of medium size. Dorsal cup not as high as wide, strongly 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 surface 
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, 
