130 
PALAEONTOLOGY OF NEW YORK. 
two species are distinguished from the forms which follow by the large anterior 
end which is separated from the body by a broad byssal depression. 
Formation and locality. In a coarse sandstone, from a bowlder containing the 
same associated fossils as a sandstone at Portville, Cattaraugus Co., N. Y.; 
probably of the Upper Chemung group; Smethport, McKean county, Pa. 
Ptychopteria sinuosa. 
PLATE XXDI, FIG. 13 ; PLATE LXXXY, FIG 8. 
Ptychopteria sinuosa, Hall. Pal. N. Y., vol. v, pt. 2. Plates and Explanations: PI. 23, fig. 13. Jan., 1883. 
Shell of medium size, rhomboidal; body narrow-ovate, oblique at an angle of 
about 40° with the hinge; length more than one-third greater than the 
height; ante-byssal margin nearly vertical, curving into the broad sinus; 
base broadly rounded; posterior margin recurving into the wing. 
Left valve convex below, gibbous in the middle and above. Right valve 
unknown. 
Hinge-line straight, length four-fifths the length of the shell. 
Beak at about the anterior third of the hinge, acute, directed forward. 
Umbonal region strongly gibbous, limited by the abrupt depression of the 
body on the posterior side, and by the byssal depression on the anterior side. 
Umbonal angle about 30°. 
Anterior end large, narrow, rounded, defined by a broad, shallow, nearly 
vertical byssal depression; ex-tremity angular. Wing narrow-triangular, 
extending nearly to the posterior extremity of the body; margin nearly 
vertical, slightly concave ; extremity somewhat produced, angular. 
Surface marked by fine undulating radii, which are less conspicuous on the 
wing, and by fine concentric lines of growth, which are crowded into sub¬ 
imbricating lamellae. On the anterior side of the body the rays are cancel¬ 
lated by the elevated concentric striae. 
The ligamental area shows a sharp linear groove extending three-fourths 
of its length posterior to the beak, and a narrow cardinal tooth anterior to the 
beak and parallel to the hinge. 
