70 
PALAEONTOLOGY OF NEW YORK. 
Pterinopecten regularis, n. sp. 
PLATE LXXXIII, FIG. 1. 
Shell of medium size, semi-circular, body of the valve oblique; length nearly 
one-fifth greater than the height, greatest length above the middle; margins 
very full and regularly rounded from the byssal sinus to the posterior extrem¬ 
ity of the hinge. 
Left valve moderately convex. Right valve unknown. 
Hinge line straight, anterior; length a little greater than the length of 
the valve. 
Beak of left valve acute, directed forward, situated anterior to the middle 
of the hinge. 
Anterior ear small, triangular, more than half as long as the posterior 
ear, limited by a broad sulcus; margin convex; extremity rounded. Posterior 
ear large and undefined from the body of the valve; margin convex, in 
regular continuation with the pallial margin; extremity obtuse, angular. 
Byssal sinus broad. 
Test thin, marked with numerous fine, alternating, filiform, elevated striae 
which are crossed by irregular lines of growth. The ornamentation of the 
ears is somewhat more subdued than on the body of the valve. 
Muscular impression small, ovate, situated below the middle of the post¬ 
cardinal slope. 
A specimen of the. left valve has a length of 24 mm., height 19 mm., 
hirige-line 25 mm. A larger example measures 30 mm. in length. 
This species is distinguished for the regular continuous convex curvature of 
the outline from the byssal sinus to the posterior extremity of the hinge. In 
this respect it differs from any other form of this genus here described. The 
right valve of P. jilitextus has a similar outline, but the left valve has been 
shown to have the margin of the posterior ear concave and the extremity 
acute-angular. The specimen of the right valve of that species, figured in 
