60 PALAEONTOLOGY OF NEW YORK. 



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

 of the hinge-margin. 



The specimen has a length of 18 mm., height 11 mm., hinge-line Ifi.o mm. 



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

 differs in its proportionally longer hinge-line, more extended posterior ear, 

 (•ompai;iti\ el\- larger anterior ear, and the greatest convexity is nearer the beak. 



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

 Tlie particular locality unknown. 



Pterinopecten nodosus, n. sj). 



PL.VTE LXXXn, 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 anti-rior 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 

 striie, witli 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 tlic left valve: l)ut 

 it is so remarkable in its nodose umlulations tlmt it is readily distinguished 

 from every other form. 



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

 Ohio, near Louisville, Ky. 



