78 



PALAEONTOLOGY OF NEW-YOKK. 



Fig-. 3 /. A cast of this species. The stone being granular, the mark a of the muscular im- 

 pression is not well defined. 



Fig. 4 «, J, c, d. Ventral, profile, cardinal, and front views of a young shell, apparently of the 

 same species. The width and length are nearly equal, and the surface is marked by 

 conspicuous lines of growth with intermediate finer concentric lines. It differs from 

 the young of A. naviformis in being wider, less convex, and having the beak of 

 the dorsal valve smaller and less strongly incurved. 



Position and locality. This species is quite common in the upper limestone at Lockport, 

 and probably elsewhere. The young specimen is from the same limestone at Sodus point, 

 Wayne county. (Co//echo?i o/ Col. J kwett.) 



467. 38. ATRYPA (Cast). 



Pl. XXIV. Fig. 5 a, b. 



The figures represent a cast of a species of Atrypa, common in the ferruginous sandstone 

 of the group. The cast of the rostral cavity is remarkably prominent and extended, and 

 slightly incurved. The cast of the muscular impression on either side is marked by three 

 distinct ridges, and in the portion below the beak are several other similar folds or ridges. 



The rock in which it occurs is usually so friable that the more minute characters are not 

 preserved. The cast is the only remaining evidence we have of the existence of this species, 

 which, during a limited period, was quite abundant. 



Fig. 5 a. Cast of dorsal valve. 

 Fig. 5 b. Profile of the same. 



Position and locality. In the friable ferruginous beds associated with the ore beds of the 

 group in Kirkland, Oneida county. {State Collection.) 



468. 39. ATRYPA CYLINDRICA 1 (Cast). 



Pl. XXIV. Fig. 6 a, b. 

 This cast is of a crushed and imperfect specimen, which is apparently the ^. cylindrica. 

 That portion extending into the beak is remarkably straight, fiat, and thin : below this is a 

 prominent triangular elevation, filling the muscular cavity. This elevated portion is margined 

 on each side by a thin elevated ridge, having a stronger but less elevated one in the middle, 

 and a smaller one on each side of the central one, halfway between it and the marginal ridge. 

 On each side of the muscular impression, the cast is marked by prominent points for the at- 

 tachment of muscular fibres. 



Fig. 6 a. Dorsal view of cast. 

 Fig. 6 h. Profile view of the same. 



Position and locality. Upper part of Clinton group at Lockport. 



