140 PALJEONTOLOGY OF NEW-YORK. 



177. 10. ATRYPA DEFLECTA { 7!. «;>.). 



Pl. XXXIII. Figs. 4 a, b. 



Sub-planoconvex, with the margins compressed, and deflected towards the front ; length 

 and breadth about equal ; cardinal line somewhat extended, curved ; dorsal valve with a 

 prominent ridge along the middle; beak extended, prominent, incurved; ventral valve 

 depressed-convex, with a mesial sinus ; surface with about 20 small regular radiating striae, 

 which are rarely divided towards the margin. 



A few specimens only of this shell have been found ; in these, the form is constant, as 

 represented in the figure ; but the markings and general aspect approximate it to the next 

 species. 



Fig. 4 a. View of dorsal valve, b. Front view, showing the form of the two valves. 



Position and locality. Near Martinsburgh, Lewis county, in the central part of the 

 Trenton limestone. 



178. 11. ATRYPA RECURVIROSTRA (n. 5/j.). 



Pl. XXXIII. Figs. 5 a, b, c, d. 



Elliptical, somewhat ovoid, very symmetrical ; breadth one fourth of an inch, length a 

 little greater ; dorsal valve with the middle elevated, regularly convex on the sides, the 

 beak extended and gracefully incurved over the beak of the ventral valve, which is re- 

 gularly convex, with a slight longitudinal depression ; surface of each valve marked by 

 about 24 regular simple longitudinal stria-, which continue entirely to the beak. 



The preceding species approximates to this one in general form and character of stria ; 

 but the sides are more expanded, and the shell has a distinct mesial sinus and elevation. 

 These characters usually increase with the age of a shell ; and since the form of the one 

 under consideration is very constant in a large number of specimens, which are of nearly 

 uniform size, and smaller than the one figured, we may presume that it is a distinct species. 

 It will be readily recognizetl by its rotund synnuetrical form, which is more elongated, and 

 more finely and evenly striated than any other species in the rock, except the preceding 

 one. 



Fig. 5 a. Dorsal valve. 

 Fig. 5 b. Profile view. 



Fig. 5 c. Cardinal view, showing tlie incurved beak of the dorsal valve. 



Fig. 5 d. Ventral valve separated from the dorsal. This valve is nearly circular, the beak being scarcely 

 extended beyond the cardinal margin. 



Position and localiiij. This shell occurs in considerable numbers in a compact greyish 

 blue l)cd of limestone near the centre of the Trenton limestone, near Martinsburgh, Lewis 

 county. It has also been seen at Lowville and at Middlevillc. (•*'''"''' Collection.) 



