288 PAUEONTOLOOY OP NEW-TOSK. 



155. 2. ORTHIS TESTUDINARIA. 



Pl. LXXIX. Figs. 4 a, b, c, d> e. 

 Reference p*g. 117, pi. 32, of thii volume. 

 In the shales of this group, this species is rarely preserved with the shell entire ; casts 

 of the interior, or impressions of the exterior of one or both valves, being the usual form 

 in which it is found. In some situations, it is almost equally as abundant as in the Trenton 

 limestone, and often attains a larger size than in that rock. 



Figs. 4 a, b. Casts of the interior of the dorsal valve. 

 Fig. 4 e. Cast of the interior of the ventral valve. 

 Fig. 4 d. A similar cast, more strongly impressed by the striae. 



Fig. 4 e. A fragment of the impression of the outer side of the ventral valve, showing the fine concentric 

 stris, which crenulate the diverging striae. 



These forms are the common ones in the shales and shaly sandstones of this group. It 

 is rarely that we find casts in the Trenton limestone, and almost equally rare to find the 

 shell preserved in this group. In this condition, it presents some slight differences from the 

 same shell in the limestone below ; but it is by no means a distinct species, as has been 

 represented. 



Position and locality. This species rarely, or never, appears in the Utica slate, but re- 

 appears near the middle of the Hudson-river shales, and continues nearly to their 

 termination j being abundant at Turin, Loraine, Pulaski, and other places. It is more 

 rarely found in the vicinity of the Hudson river, and in the Mohawk valley. 



(State ColUetion.) 



341. 19. ORTHIS? ERRATIC A (n.yp.). 



Pl. LXXIX. Figs. 5 a, b, c, d, e,f. 



Subhemispherical, orbicular ; dorsal valve very convex, with the mesial portion abruptly 

 elevated, flat above ; ventral valve convex at the sides, depressed in the middle, and 

 considerably elevated in front $ surface marked by fine simple uniform stria:. 



This species is usually found in great numbers, in erratic masses of the sandstones of 

 this formation, associated with Orthis testudinaria, Cyrtolites ornatus, and other fossils of 

 the group. It has rarely been found in the rocks in place. It is distinguished from Orthis 

 testudinaria, which it most resembles, by its more rotund form, and broader mesial 

 elevation and depression ; the striae .are also more simple and straight, scarcely curving 

 towards the cardinal margin. It is unknown in the Trenton limestone. 



Figs. 5 a, b. Dorsal and ventral views of the cast of a large specimen. 



Fig. 5 e. Ventral view of a small specimen. 



Fig. 5 d. Front view of a larger specimen. 



Fig. 5 e. Cardinal view of a large specimen. 



Fig. 5 /. Profile view of a moderately convex specimen. 



