10 
PALEONTOLOGY OF NEW YORK. 
Hinge-line straight, extending as far as the anterior margin; length two- 
thirds the height of the shell; ligamental area narrow. 
Beaks well-defined, not rising above the hinge-line, situated anterior to 
the middle. 
Posterior ear large, triangular, margin concave; the ornamentation differ¬ 
ing from that on the umbo; defined by a slight depression and a change of 
convexity. Anterior ear small, defined by a well-marked sulcus; byssal 
sinus deep; margin convex near the extremity of the hinge-line. The area 
of the posterior ear is more than twice that of the anterior. 
Test ornamented by about 35 rounded, radiating costae, with intermediate 
smaller ones, crossed and crenulated by regular striae of growth, of which 
there are about 10 in the space of 5 mm. On the ears the radiating lines 
are present, especially on the anterior ear, and the concentric striae are more 
crowded than on the body of the shell. 
The characters of the interior are not preserved. 
The largest specimen has a length of 32 mm., and the hinge-line measures 
23 mm. A smaller specimen, preserving both valves, has a length of 29 
mm., and height about equal. 
This species is distinguished from A. exacutus by the greater angle subtended 
by the sides of the umbo, by its greater obliquity, and the less sharp radiating 
costae of the surface. In A. Phorcus the length is comparatively greater and 
hinge-line shorter, the ears smaller, and the strong crenulating striae of 
growth do not occur. 
Formation and localities. In the shales of the Hamilton group, at Fultonham, 
Schoharie county; and Hamilton, Madison county, N. Y. 
Aviculopecten Phorcus. 
PLATE V, FIG. 22. 
Aviculojpecten Phorcus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 5, fig-. 22. Jan., 1883. 
Shell of medium size, obliquely ovate; height and length equal; anterior and 
basal margins regularly rounded, becoming more convex towards the middle 
