152 
PALAEONTOLOGY OF NEW YORK. 
Ptychopteria expansa. 
PLATE XXIII, FIGS. 10, 11. 
Ptychopteria expansa. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 23, figs. 10, 11. 
Jan., 1883. 
Shell of medium size, sub-rhomboidal; body ovate, oblique at an angle of 
about 60° with the hinge-line; length one-fifth greater than the height; 
ante-byssal margin oblique, gently curving into the shallow sinus; basal 
margin broadly rounded to the base of the wing. 
Left valve convex below, gibbous above. Right valve unknown. 
Hinge-line straight, central, length greater than the length of the valve. 
Beak at about the anterior fifth of the hinge, inclined acutely forward, 
moderately prominent. Umbonal angle acute. 
Anterior end small, surface convex to the nearly vertical byssal depression 
which extends half way to the base of the shell; extremity compressed and 
acute. Wing very large, triangular, extended, joining the body at the 
posterior extremity; the furrow obscurely marked ; margin gently concave, 
extending backward ; extremity produced. 
Surface marked by regular strong radii and by concentric lines of growth. 
The concentric striae are sometimes crowded into irregular fascicles, giving 
an undulated appearance to the surface; the radii are strong on the umbonal 
slope, less conspicuous on the wing, and on the antero-basal portion they are 
interrupted, and oblique to those on the umbo. 
Interior unknown. 
The specimen described has a length of 27 mm., height 22 mm., and hinge¬ 
line 30 mm. 
This species is distinguished by its erect form, large and extended wing, and 
peculiar character of surface markings. The furrow of the wing is indicated 
only by a wider depression between the radii, and a stronger ray marks the 
fold. 
Formation and locality. In a coarse sandstone of the Chemung group near 
Smethport, Pa. 
