LAMELLIBRANCHIA TA. 
133 
Anterior end short, small, acute, limited by a shallow byssal depression. 
Wing large, triangular, extending to near the posterior extremity of the body; 
margin slightly oblique, scarcely concave; extremity apparently not produced. 
Surface marked by fine radii which are more or less interrupted by the 
varices of the concentric striae, and are frequently undulating. The concentric 
striae are often fasciculate, and in their usual condition give an undulated 
appearance to the cast, but where well-preserved they are angular and some¬ 
what lamellose. 
Interior unknown, except a narrow groove along the ligamental area of 
the hinge. 
A left valve of usual dimensions has a length of 30 mm., height 19 mm., 
hinge-line 23 mm. A similar right valve has a length of 31 mm., height 18 
mm., and hinge-line 22 mm. 
This species differs from P. Proto in its less angular posterior slope and 
posterior end; the margin of the wing is less oblique to the hinge and the 
extremity is not produced. 
The specimens occurring in a conglomerate or coarse sandstone have been 
subjected to different degrees of pressure and maceration, and consequently 
present a great variety of aspect in the surface ornamentation. The furrow 
and fold limiting the wing are always less conspicuous in the left valve; and 
in some cases when the shell has suffered pressure these characters are very 
obscure. 
Formation and locality. Abundant in a conglomerate of the Chemung group 
at Panama, Chautauqua county, N. Y. 
Ptychopteria Eucrate. 
PLATE XXXII, FIG. 24; PLATE LXXXV, FIGS. 27, 28. 
Ptychopteria Eucrate, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 23, fig. 24. Jan., 1883. 
Shell above the medium size, rhomboidal; body very narrow, elongate-ovate, 
oblique at an angle of about 30° with the hinge-line; length nearly twice 
the height; ante-byssal margin oblique, curving into the sinus; the ventral 
