148 PALEONTOLOGY OF NEW YORK. 



Ptvihopteria Thalia, n. sp. 



IM.ATE I, XXXV, FIGS. 32, :«. 



Shell of medium «ize, rhomboidal ; body ovate, oblique at an an^le of about 45° 

 with the cardinal line; Iciiiith one-third greater than the hei^lit : aiitciior 

 .and basal margins broadly rounded, slightly impressed by the byssal sinus; 

 post-basal extremity sub-angular, abruptly recurved. 



Left valve extremely gibbous, the point of greatest convexity is one- 

 third of the height from the beak. Right valve convex on the umbo, 

 depressed-convex below. 



Ilinge-line straight, a little less tluui the greatest length ol' the slirll. 



Beak situated at the anterior third of the binge, prominent in the left 

 valve, curving over the hinge-line. Umbonal region abruptly gibbous in the 

 left valve, distinctly limited, subtending an acute angle. 



Anterior end comparatively large, limited by a nearly vertical shallow 

 byssal depression ; margin convex ; extremity acute. Wing small, distinctly 

 limited by the post-unilional I'iutow : margin oliliijuely tnnicate, a little 

 convex ; extremity obtuse-angled. 



Surface of both valves marked by fine radii originating on the umbo, 

 becoming stronger on the lower part of the body, less conspicuous on the 

 wing, and oljsolete on the anterior end ; and by lines of growth which 

 are lamellose on the anterior side and produce unequal concentric ridges on 

 the body of the valve. 



Interior luiknown. 



A left valve has a length of 25 mm., height 17 mm., ami hinge-line 

 23 mm. A small right valve has a length of "Jd mm., height 1') mm., and 

 hinge-line l(i mm. 



This species resembles P. perlata Imt the wing is comparatively smaller, 

 extremity not acuminate, and the umlio more gibbous. 



Formation and loralili/. In a sandstone of the I piicr ( 'lirmnm.:' group at .Vlk'- 

 ghany Springs, Warren comity, l*a. 



