*2 



PLATYCRINUS FORMOSUS, n. Sp. 



Plate IV, Fig. 20, basal view; Fig. 21, azygous side view pre- 

 serving the first azygous plate. 



This species is about medium size and belongs to the discoid 

 forms. Calyx shallow, pentagonal, four times as wide as high. 

 Plates thick, sculptured. Sutures canaliculate. The surface is 

 ornamented with a rounded ridge upon each side of the canalic- 

 ulated sutures which bears more or less conspicuous rounded 

 nodes. Column round. 



Basal s form a concave pentagonal disc, bordered by ah angu- 

 lar nodose rim, that adjoins the canaliculated suture. The con- 

 cavity is equal to the thickness of the plates and commences at 

 the angular ridge adjoining the suture. The plates are ser- 

 rated for the attachment of the column. The first radials pro- 

 ject, at first, horizontally, and then curve upward, having a 

 constriction in the middle part, beyound which they are direct- 

 ed horizontally, and the facet, for the second plate, is trans 

 verse or nearly perpendicular. Each articulating facet forms 

 almost a circle, having a diameter more than one third the 

 diameter of the plate, and being only slightly notched for the 

 ambulacral canal. 



The angles for the reception of the regular interradials are 

 very obtuse, and the angle for the reception of the first azy- 

 gous plate is moderately acute. The first azygous plate is pen- 

 tagonal, stands upright and indicates a large area on account 

 of its width, but it is shorter than the same plate in P. tug- 

 uriurn, and the probability is that the vault is less convex. 



The calyx of this species has some resemblance in form to 

 P. truncaius, but in that species, the base is flat and the sur- 

 face is not ornamented, while in this species, the basal disc is 

 quite concave and the column is inserted into the concavity 

 and the surface is ornamented with ridges and nodes. Other 

 differences in form, occur in the parts preserved. It cannot 

 be mistaken for any other described species by any one capa- 

 ble of distinguishing specific characters. 



Found by R. A. Blair, in the Burlington Group, at Sedalia, 

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



