LAMELLIBRANCHIA TA. 
47 
Compared with L. magnificus, this species has greater convexity, less elevated 
radii, and, in general, a comparatively greater longitudinal diameter. It differs 
from L. cymbalon and L. tricostatus in surface ornamentation. 
This species, described from only the left valve, is nevertheless so distinctly 
unlike any others here described that it is readily recognized. 
Formation and localities. In the coarse beds of the Hamilton group, at Ham¬ 
ilton, Madison county; and Worcester, Otsego county, N. Y. 
Lyriopecten cymbalon. 
PLATE XXIV, FIG. 8. 
Lynopecten cymbalon, Hall. Pal. N. ‘Y., vol. v, pt. 5. Plates and Explanations: PI. 24, fig. 8. Jan., 1883. 
Shell large, sub-orbicular, not oblique; height a little less than the longitudinal 
diameter; pallial margin regularly rounded, upper anterior margin more 
inflated than the posterior, which is truncated toward the beak. 
Left valve regularly convex; the basal margin slightly inflected, giving 
the valve an undue convexity. Right valve not known. 
Hinge-line straight, length a little greater than one-half the longitudinal 
diameter of the shell, and extending about one-third of its length farther to 
the posterior than to the anterior margin. 
Beak obtuse, rounded, straight, central; umbonal region defined by its 
abrupt antero- and post-cardinal margins, and by its convexity. 
Anterior ear very small, narrow-triangular; margin concave; extremity 
obtuse-angular; byssal notch broad and shallow, not conspicuous. Posterior 
ear large, triangular, marked by a deep sinus; margin convex; extremity 
angular; length twice as great as the anterior ear. 
Test marked by about twelve very strong, continuous, broad, rounded 
rays, with from one to six smaller ones of variable strength in each of the 
flat interspaces; crossed by fine, sharp, regular, concentric striae of growth, 
which are elevated into lamellar ridges at irregular intervals. The ears and 
a broad adjacent space on the body of the valve are destitute of rays, hut 
show strong striae and undulations of growth. The direction and character 
