?5 



expands to the top of the basals, and, from there, expands 

 more rapidly to the facets for the second radials, which gives 

 it a pentagonal outline on toj:). Sutures between the radials 

 and between the basals and radials beveled. Surface granular. 

 Plates thick. Column round and large. 



Basals form a short subcylindrical cup, with an expanded 

 base. First radials of unequal size, differing as much in width 

 as in length, and subquadrate in outline; they are longitudi- 

 nally convex in the central jjart, i)rojecting most at the articu- 

 lating facets for the second radials, and depressed at the 

 longitudinal sutures. Articulating facets large, occupying 

 ab(Mit two- thirds the width of each plate, and sloping down- 

 Ward .so as to be directed at an angle of sixty degrees, from a 

 perpendicular line. The azygous interradial is large and stands 

 nearly upright. The angles for the reception of the regular 

 interradials are very obtiise. 



This sjiecies will be readily distinguished, by its general 

 form and thick platDS, from all others. It bears most resem- 

 blance to Plalycrimis allophylus. 



Pound by R. A. Blair, in the Chouteau limestone, at Sedalia, 

 Missouri, and now in the collection of S. A. Miller. 



PLATYCRINUS SULCIPERUS, n. Sp. 



Plate IV, Fig. 33, basal view; Fif/. 34, side view. 



■ Species above medium size and belongs to the discoid forms. 



Calyx shallow, pentagonal, two and a half times as wide as 



high. Plates thick, fun-owed. Sutures broadly beveled. 



Basal disc large, pentagonal, concave in the central part and 

 having a furrow just within the pentagonal border. First ra- 

 dials wider than high, project at an angle of about forty-five 

 degrees, sharply constricted below the facets for the second 

 radials. The facets are semi-elliptical, directed horizontally, 

 and broadly notched for the ambulacral canal. There is a fur- 

 row just within the beveled edge adjoining the basal disc, and 

 one on each side of each plate adjoining the beveled suture. 

 The angles for the recejition of the regular interradials are 

 obtuse The valt and arms are unknown. 



This species is distinguished from other discoid species hav- 

 ing bev(^led sutures, by the furrow within the border of each 

 plate, without other ornamentation by the sharp angular con- 



