LAMELLIBRANCHIA TA. 
65 
The largest specimen has a length of 19 mm., height 29 mm., hinge-line 
29 mm. 
This species is very similar in form to P. Icetus; but the hinge-line is pro¬ 
portionally longer and the radii stronger and more distinctly alternating. It 
differs from P. dignatus in its more oblique form, proportionally greater diameter 
and sharper radii. From P. conspectus it differs in being much more oblique in 
outline and comparatively narrower. 
Formation and locality. In shales of the Hamilton group, Ontario county, N. Y. 
Pterinopecten spondylus. 
PLATE XVII, FIG. 16. 
Pterinopecten spondylus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 17, fig. 16. 
Jan., 1888. 
Shell small, sub-rhomboidal, scarcely oblique; body of the shell ovate; length 
somewhat greater than the height; pallia! margins regularly rounded, be¬ 
coming straight on the posterior slope, which is continuous with the margin 
of the ear. 
Left valve convex. Right valve not known. 
Hinge-line straight, length greater than the longitudinal diameter of the 
shell, extended anteriorly. 
Beak obtuse, rounded, directed forward, situated anterior to the middle 
of the hinge-line. Umbonal region prominent, but not strongly defined on 
the posterior slope; subtending an acute angle. 
Ears broad, triangular, flat. Posterior ear much the larger, scarcely 
defined; margin slightly concave; extremity rectangular. Anterior ear 
defined by a distinct sulcus; margin convex; extremity rounded. Byssal 
sinus shallow. 
Test marked by regular, sharp elevated rays, with broader interspaces 
which are marked by finer rays, and concentric foliate lamellae of growth, 
which are bent backward in crossing the rays, forming short semi-tubular 
9 
