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 13 mm., height 11 mm., hinge-line 16.5 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, 
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. 
Pteeinopecten 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 afe 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. 
