70 



PALJEONTOLOGY OF NEW-YORK. 



Fig. 3 a, b. Ventral valve of two specimens of different age. 



Fig. 3 c. Front or base of the larger specimen, showing the elevation of the sinus. 



Fig. 3 d. Profile view of the same. 



Position and locality. In the lower part of the Clinton group at Lockport. 



(Collection of Col. Jewett.) 



456. 27. ATRYPA NEGLECTA. 



Pl. XXIII. Fig. 4 a -/. 



Subpyramidal or subglobose, the beaks more or less elevated ; valves very gibbous below, 

 and tapering very abruptly to the beaks ; mesial depression and elevation moderate, marked in 

 the dorsal valve by three, and in the ventral valve by four plications ; valves on each side of 

 the mesial fold marked by from five to nine plications, which are angular and undivided to the 

 beak ; surface marked by undulating or zigzag strise, which are usually obsolete ; cardinal line 

 not extended ; beak of dorsal valve sometimes closely incurved, and in other specimens ele- 

 vated and slit beneath the apex. 



This species is also common to the Niagara group ; and though more abundant, it is never 

 so gibbous or rotund, but has a more triangular outline. 



Fig. 4 a. A specimen with seven plications on each side of the mesial fold. 

 Fig. 4 b, c. Protile and front views of the same specimen. 



Fig. 4 d, e, f. Ventral, dorsal, and profile view of a specimen with only five plications on each 

 side of the mesial fold. 



Position and locality. This species occurs in the lower part of the Clinton group at Rey- 

 nale's basin, Niagara county, associated with Jl. congesta. {State Collection.) 



457. 28. ATRYPA EQUIRADIATA. 



Pl. XXIII. Fig. da-e. 



Ovate ; base rounded ; sides long, tapering to the beak, which is small and narrow ; valves 

 nearly equally convex ; beak of the dorsal valve projecting beyond the ventral valve, and 

 slightly incurved ; cardinal line not extended ; valves without any apparent mesial depression 

 or elevation, marked by from twenty-four to thirty-two rounded plications, which are undi- 

 vided, and extend to the beak. 



This is a pretty, symmetrical species, which is known to me as occurring only in the 

 arenaceous beds of the group ; the shell is usually destroyed, leaving partial or entire casts. 

 It is distinct from any other known species in this group, but resembles one in the Niagara 

 group, from which it will be distinguished by a less proportional width, a longer beak, and 

 larger number of plications in comparison to the size. 



