686 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



the interradial plates erect. Ventral disk convex; covered with spinous 

 plates. Column small, obscurely elliptical. 



Horizon and Locality. — Chouteau limestone ; six miles southeast of 

 Sedalia, Mo. 



Types in the collection of Mr. Sampson. 



AMEBIC ANUS GROUT. 



Dorsal cup rather short and but slightly spreading ; base nearly flat ; 

 plates ornamented by coarse granules or rows of confluent nodes. 



Platycrinus americanus and Sh. 

 Flate LXXV. Figs. 10, 11, M, 13a, I, c. 



1852. Owen and Shumaed ; U. S. Geol. Surv. Wise, Iowa and Minn., p. 594, Plate ^B, Figs, la, h. 

 1881. W. and Sf.; Revision, Part II., p. 70 (Proceed. Acad. Nat. Sci. Phila., p. 2i4). 



Sjn. Plati/cr. tnaicatus Hall; Geol. Rep. Iowa, Vol. I., Part II., p. 537. 



(?) Sjn. P. Broadheadi S. A. Millek ; 1891, Geol. Surv. Missouri, Bull. 4, p. 21, Plate 2, Fig. 15. 



Calyx subglobose, a little higher than wide. Dorsal cup more than once 

 and a half as wide as high, .slightly spreading, the base broadly truncated. 

 Height of ventral disk about equal to that of the dorsal cup. Plates orna- 

 mented by coarse granules or irregular nodes, arranged in concentric lines 

 around their margins, covering the entire surface. Edges of the plates 

 beveled, and the basi-radial and interradial suture lines channeled. 



Basals forming almost a plane, rarely more than their beveled edges 

 visible in a side view; the column facet very slightly depressed ; interbasal 

 sutures indeterminable. Eadials a little spreading, one fourth wider than 

 long; the outer ends of the upper faces moderately sloping, except toward 

 the anal side where they form a deep and broad notch. Facet semicircular ; 

 the notch at the summit very small, if represented at all. Costals rather 

 large, much wider than long ; pentangular. Distichals and palmars as long 

 as the costals but narrower, a little constricted across the middle. Arms six 

 to the ray ; of moderate size, biserial above the second or third plate from 

 the bifurcation ; the joints rather long ; the pinnule sockets projecting, 

 especially in young specimens, and the pinnules strong and in contact later- 

 ally ; the proximal one being given off from the first distichals. Ventral 

 disk hemispheric, the plates convex. Orals large, rather regularly arranged. 

 Ambulacral plates small and not elevated. Interambulacrals three and two ; 

 the middle one of the first row longer than wide, that of the anal side much 



