60 PALAEONTOLOGY OF NEW YORK. 



Interior not observed. LigamentaJ area narrow, appearing as a simple fold 

 of the hinge-margin. 



The specimen lias a length of 13 mm., height 11 mm., hinge-line 16.5 mm. 



In some of the modes of occurrence, this species resembles P. exfoliatus, but 

 < 1 i tiers in its proportionally longer hinge-line, more extended posterior ear, 

 comparatively larger anterior ear, and the greatest convexity is nearer the beak. 



Formation and locality. Upper Helderberg limestone, Western New York. 

 The particular locality unknown. 



Pterinopecten nodosus, n. sp. 



PLATE LXXXII, FIG. 13. 



Shell small, sub-rhomboidal, slightly oblique ; form not fully known. 



Left valve very convex. 



Beak prominent, nearly erect. Umbonal region very prominent, the limits 

 distinct on the anterior and obscure on the posterior side ; subtending an 

 acute angle. 



Posterior ear large, triangular ; margin very slightly concave ; extremity 

 angular. Anterior ear not preserved in the specimen. 



Test thin, marked (in a partially exfoliated specimen) by strong, rounded 

 rays with intermediate finer ones, and fine, concentric, undulating, elevated 

 striae, with numerous concentric undulations, which increase in frequency 

 from the beak to the margin, and on crossing the larger rays, are elevated 

 into strong nodes. On the posterior ear the rays are fine, equal and con- 

 tinuous. 



Interior characters unknown. 



This species is described from an imperfect specimen of the left valve ; but 

 it is so remarkable in its nodose undulations that it is readily distinguished 

 from every other form. 



Formation and locality. In the Corniferous limestone at the Falls of the 

 Ohio, near Louisville, Ky. 



