136 
PALAEONTOLOGY OF NEW YORK. 
Ptvchopteria falcata, n. sp. 
PLATE LXXXV, FIGS. 6, 7. 
Shell of medium size, rhomboidal, sub-falcate; body narrow-ovate, oblique at 
an angle of about 45° with the cardinal line ; length one-fourth greater than 
the height; anterior and basal margins broadly rounded; posterior margin 
abruptly recurved. 
Left valve convex, gibbous above, arcuate. Right valve convex on the 
umbo, depressed-convex below. 
Hinge-line straight, greater than the height of the shell. 
Beak situated at about the anterior fourth of the cardinal line, prominent 
and arching over the hinge in the left valve; not elevated in the right valve. 
Umbo abruptly gibbous in the left valve, subtending an acute angle. 
Anterior end limited by a shallow, nearly vertical byssal depression, which 
inclines backward in some specimens; margin convex; extremity acuminate. 
Wing triangular, joining the body near the posterior end; margin straight, 
slightly concave just below the hinge-line; extremity acute. 
Surface of both valves marked by fine radiating striae, which are less 
conspicuous on the wing and obsolete on the anterior end; and with 
concentric striae, which are sometimes strongly lamellose, producing undu¬ 
lations of the surface. 
Interior unknown. 
A left valve has a length of 28 mm., height 22 mm., hinge line 24 mm. 
A similar right valve has a length of 28 mm., height 15 mm., and hinge-line 
24 mm. 
The shell of this species is comparatively longer, the body more oblique, and 
the wing smaller than in P. Thetis. 
Formation and locality. In a sandstone and conglomerate of the Upper 
Chemung group at Alleghany Springs, Warren county, Pa. 
