148 PALiEONTOLOGY OF NEW-YORK. 



187. 20. ATRYPA DENTATA {n.sp.). 



Pl. XXXIII. Figs. 14 a, b, e. 



Pyramidal, subtriangular ; breadth somewhat greater than the length ; cardinal line 

 short ; margins of the shell sloping abruptly downwards ; surface marked by about eight 

 or nine strong and deep plications, two of which are much elevated on the mesial fold of 

 the ventral valve ; dorsal valve with the sinus broad, deep and angular, with a single 

 plication in the centre, extremely elevated in front j plications crossed by zigzag or ad- 

 vancing and retreating filiform lines ; beak of the dorsal valve small, acute, incurved, with 

 no visible perforation. 



This remarkable litlle shell is distinguished by its deep mesial sinus and strong plications, 

 particularly the central ones. The plaits are simple, reaching entirely to the beak, and 

 enlarging rapidly below. An analogous species, the ^. duplicata, with fewer plications, 

 occurs in the Chemung group. 



Fig. 14 a. Dorsal valve. 



Fig. 14 A. Front view of the same; the dorsal valve below. 



Fig. 14 c. Profile view. 



Position and locality. In the higher part of the Trenton limestone at Turin, Lewis county. 



{VoUrction of Mr. Alson Clauke, on whose authority I have placed it among the Trenton species, not having 

 mysf If collected the same from the rock.) 



188. 21. ATRYPA SORDIDA (7(.sp.). 



Pl. XXXIII. Fig. 1(5. 



Circular : valves equally convex ; beak of the dorsal valve extended beyond the other ; 

 surface marked by small simple radiating strife, which are crossed by elevated lines, giving 

 a rugose appearance ; no mesial sinus or elevation. 



This is pfobably a young shell, having the sharp striae more distant than the spaces 

 between them. 



The precise locality of this specimen is uncertain, but, from its association, there can be 

 no doubt of its position being that of the Trenlon limestone. 



