72 



PLATYCRINUS FORMOSUS, n. Sp. 



ridle 7T^, Fifj. 20, basal view; Fig. 21, azygous side view pre- 

 serving the fimt azygous pl(iie. 



This species is aboat medium size and belongs to the discoid 

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

 Plates thick, sculptured. Sutures canaliculate. The surface is 

 ornamented with a I'ounded ridge ujjon each side of the canalic- 

 ulated sutures which bears more or less conspicuous rounded 

 nodes. Column round. 



Basals form a concave pentagonal disc, bordered by an 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 u^jward, 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 

 anibulacral canal. 



The angles for the reception of the regular interradials are 

 vei'y obtuse, and the angle for the reception of the first azj-- 

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

 tagonal, stands upright and indicates a large ai"ea on account 

 of its width, l)ut it is shorter than the same plate in P. iiig- 

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



The calyx of this species has some resemblance in form to 

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

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

 (juite concave and the column is inserted into the concavity 

 and the surface is ornamented with ridges and nodes. Othi i- 

 differences in form, occur in the parts preserved. It cannct 

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

 ble of distinguishing specific characters. 



Pound by R. A. Blair, in the Bui-lington Group, at Scdalia, 

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



