40(1 PALAEONTOLOGY OF NEW-YORK. 



crinoidej: of the oriskany sandstone. 



The Crinoideae of this rock are described in connection with those of the 

 Lower Helderberg group in the first part of the volume ( See page 138). 

 The plates (85, 86, 87 & 88) illustrating these fossils are arranged in 

 their order of sequence among those of the Oriskany sandstone. 



BRACHIOPODA OF THE ORISKANY SANDSTONE. 



The generic identity of the Brachiopoda of this rock with those of the 

 Lower Helderberg group has already been noticed. The most marked 

 difference consists in the generally larger size of the species of the same 

 genera, and in the great number of individuals of the same species ; while 

 the absence of Pentamerus (with the exception of an obscure specimen) 

 from the strata of this age in New- York is remarkable, and the Genus Me- 

 BISTA, so far as we at present know, is represented onlyin a single species. 



Discina ^^randis ( n. s.). 



Plate XCII. Fio. 1 a, b, c, d. 



Shell suborbicular or very broadly oval. Dorsal valve very convex, the 

 convexity equalling about one-third of the width : apex subcentral. 

 Ventral valve nearly flat : apex somewhat exccntric, very slightly 

 elevated in front of the foramen, and the space between this and the 

 anterior margin slightly concave ; foramen oblong, narrow oval, the 

 depression on the exterior of the shell extending from the apex to near 

 the posterior edge. 



ScEFACE marked by strong elevated concentric lamellose striae, and, on 

 the interior of the shell, by radiating vascular impressions. 



