LAMELLIBRANCHIA TA. 
23 
Ligamental area narrow, well-marked, its width is .5 mm. in a specimen of 
20 mm. in height. 
The original specimen of this species is 20 mm. in height, 18 mm. in 
length, and the hinge-line 13 mm. Another specimen is 13 mm. in height, 
11 mm. in length, hinge-line 8 mm. The largest specimen found has a 
height of 22 mm. 
This species resembles A. celsus more nearly than any other form here 
described; it differs from that one by its much smaller ears with concave 
margins, more obtuse umbo, regular, equal striae, and comparatively shorter 
form. The two species agree in the non-obliquity of the body of the shell to 
the hinge-line. This species has a vertical range from the middle to the upper 
members of the Chemung group, but is not abundant. 
Formation and localities. In the Chemung group at Painted Post, Steuben 
county; Chemung Narrows, Tioga county, N. Y.; and in Bradford, Tioga and 
Warren counties, Pennsylvania. 
Aviculopecten celsus. 
PLATE VII, FIGS. 29, 30. 
Aviculopecten altus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 7, figs. 29, 30. 
Jan., 1883. 
Not Aviculopecten altus, White. Bull. U. S. Geol. Surv., vol. v, p. 110. 1879. 
Shell small, ovate cuneiform, sub-equilateral, not oblique; height one-fifth 
greater than the length; pallial margin rounded to near the ears, where the 
sides of the shell are nearly straight. 
Right valve convex; the greatest convexity being equal to one-fourth the 
length of the hinge-line. Left valve not observed. 
Hinge-line straight, length three-fourths the length of the shell, not extend¬ 
ing as far as either lateral margin. 
Beak acute, straight, extremity pointed, arching over the hinge-line; umbo 
prominent, subtending an angle of 80°. 
Ears broad-triangular, large, flat, sub-equal, the margins slightly convex; 
extremities rectangular; separated from the body of the shell by a moderate 
