Tii PALJEONTOLOGY OF NEW YORK. 



This spt'fies resonil)k's Pterinea reprobvs, from the shales of the Chemung 

 f^roiij) at Ithaca, wliich has straighter and more rounded radii in the left valve, 

 with sharper intermediate radii and more elevated, undulating, concentric strife. 

 Till' right valve of that species is more convex with stronger and often dupli- 

 cating radii ; wliiU' the l)yssal sinus is less distinctly marked. The present 

 species differs from Pterinopeden dispandus in its greater length, projjortionally 

 longer hinge-line, less strongly marked right valve, and want of duplicaticm 

 in the radii. 



Formation and locality. This species iscomiium in the shales of the Ilainilton 

 group at Bear gulf, Schoharie county, N. Y. 



Ptekinopecten undosus. 



PI.ATK II, FIOS. 10-I!I; AM) rLATK LXXXIl, FIG. 7. 



Avicatitpeiten undrtlatus. Hall. M.S. 1877. 



" " " Cat. Amer. Palieozoic Fo.ssils. S A. Millkk. 1877. 



Not Pecteii undiUatits, McCoy. Carb. Foss. of Iielami, p. 101, pi. xvii, fig. 12. 1844. 

 Not Aril iilitjKtten imdiilatn.^, McCoy. 1853. 



Pterimipeiiett undositSy Hall. Pal. N. Y., vol. v, pt. 1. Plate.s aiRi Explanations: PI. 2, tig-s. 10-19. 



.Jan., 1883. 



Shell larL^cr tlian medium, rhdiiilioidal or siil)-urbicular ; left valve moderately 

 oblique ; right valve scarcely oblique ; length one-third greater than the 

 height, proportionally shorter in young shells ami in tlic riglit valve; ante- 

 rior and l)asal margins regularly rounded, .sonu'what i)r()(lucc(l l)eliinil. and 

 receding rapidly toward the hinge-line. 



Valves nearly equally convex ; the riglil valve a little less convex, more 

 orbicular in outline, with deep byssal notch, and different surface markings. 

 When occurring in the softer shales, the valves are often (k'j)ressed-convex. 



Hinge-line straight, length a little li'ss than the height of the shell, nearly 

 central. 



Beak obtuse, rounded, scarcely rising above the hinge-line, anterior to the 

 middle of the shell, inclined forward. Umbonal region ample, well-defiiied, 

 subtending a very obtuse angle. 



