LAMELLIBRANCHIA TA. 
21 
d’Orbigny), the valve is more convex, beak more obtuse, and the concentric 
marking forms a prominent feature. 
Formation and locality. In the Chemung group at Conewango, Cattaraugus 
county, N. Y. 
Aviculopecten plenus. 
PLATE XXXV, FIG. 3. 
Aviculopedehplenus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 24, tig. 3. Jan., 1883. 
Shell sub-orbicular, sub-equilateral; transverse axis nearly vertical to the 
hinge-line; height one-sixth less than the length, giving a marked fullness 
to the outline of the sides. 
Left valve convex, the convexity equal to one-sixth the length of the 
shell. The point of greatest convexity distant one-third the length from 
the beak. Right valve not observed. 
Hinge-line straight, nearly central, the length more than two-thirds the 
length of the shell. 
Beak obtuse, situated centrally with regard to the hinge-line, and also to 
the body of the shell; umbo rounded. 
Ears sub-equal, triangular. Posterior ear mucronate at the extremity; 
margin deeply concave. Anterior ear acute at the extremity, and the margins 
convex; separated from the umbo by an abruptly sloping sulcus extending 
to the beak. 
Surface ornamented with about 130 regular, rounded, close, filiform radii, 
crossed by very fine, sharp, concentric striae. The surface markings are 
present on the ears, the radii distinct and stronger than on the adjacent 
portions of the shell. The rays become more frequent and finer from the 
basal margin in both directions towards the ears. 
Interior not preserved in the specimen described. 
The height of the specimen is 25 mm., length 30 mm., hinge-line 21 mm. 
On the lower margin there are 9 rays in the space of 5 mm. 
