660 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



their surface smooth ; basi-radial and interradial suture lines distinct, but not 

 grooved. 



Basals forming a low basin, with a short rim extending outward from the 

 lower end; the bottom slightly excavated for the reception of the stem; the 

 plates closely anchylosed, and interbasal sutures invisible. Column facet 

 large, circular, the extreme outer margin striated ; axial canal very small. 

 Radials as wide as long, a fifth wider near the top than at the bottom, 

 thickened around the facets ; the sides supporting the interradials very 

 short. Facets unusually wide, occupying three fourths the width of the 

 plates, directed obliquely upwards, a little concave, and provided with a low 

 transverse ridge. The costals occupy the whole width of the facet, are 

 extremely short, and very slightly angular ; their sloping faces with a trans- 

 verse ridge and a shallow fossa to the outer side of it. Structure of all 

 other parts unknown. 



Horizon and Locality. — Chouteau group, at Pin Hook bridge, Mo. 



Ty^^e in the collection of Mr. Sampson. 



Platycrinus pisum Rowley and Haeb. 



Plate LXXI. Figs. 13a, h. 

 1891. Kansas City Scientist, p. 113, Plate 3, Yig. 3. 



A very small species. Calyx spherical, about as wide as high, the dorsal 

 cup a little higher than the tegmen, the sides almost at right angles to the 

 truncated base. Plates finely granular, the sutures moderately grooved, 

 except those between the basals, which are invisible. 



Base disk-like, fiat, only the edges curving upwards ; the place of attach- 

 ment for the column circular, elevated slightly above the plane of the base ; 

 its extreme outer margin striated. Radials a little wider than long, the 

 sides parallel ; facets occupying half the width of the plates, and nearly 

 a third of their length, semicircular, having no notch at the upper edge. 

 Interradial plates somewhat depressed and directed obliquely upwards, ex- 

 cept at the anal side, where they are erect and form the base of a rather 

 prominent anal protuberance, composed of minute plates. The orals are 

 large and convex ; they rest upon the first row of interradials and against 

 a large radial dome plate, there being no covering plates in the calyx. 

 Structure of arms unknown. 



