LAMELLIBRANCHIA TA. 
11 
of the posterior side, and thence concave to the beaks, giving the shell an 
appearance of considerable amplitude behind. 
Left valve regularly and moderately convex. The right valve is unknown. 
Hinge-line straight, about one-half the length of the shell. 
Beak rounded, extending to and situated near the centre of the hinge-line; 
umbonal angle smaller than usual, being about 90°. 
Ears comparatively small, triangular, with concave margins ; posterior ear 
the larger, separated from the body of the shell by a difference in convexity 
and the absence of radiating lines; anterior ear defined by a sulcus. 
Test marked by about 60 fine, rounded, radiating costae, with a few inter¬ 
mediate smaller ones, and fine striae of growth. The rays are absent on the 
ears, but the lines of growth are more distinct than on the body of the shell. 
The characters of the interior have not been observed. 
The specimen described has a height of 37 mm., and a greatest length of 
26 mm. 
This species differs from A. formio by its smaller ears, their distinct character, 
and the general surface-markings. It resembles young individuals of A. 
princeps; but the comparative size and extent of the ears are very different, 
while the body of the shell is more constricted at the base of the ears. A. 
fasciculatus is very similar in the general form of the body of the shell; but the 
length is greater than the height. The alae and the ornamentation of the test 
are distinguishing characters. 
Formation and locality. Hamilton group, Schoharie, N. Y. 
Aviculopecten fasciculatus. 
PLATE V, FIGS. 9-17; and PLATE LXXXI, FIGS. lHt. 
Aviculopecten fasciculatus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 5, figs. 9, 10, 
12, 16, 17. Jan.. 1883. 
Aviculopecten repletus. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 5, figs. 13-15. Jan., 1883. 
“ Orestes, “ “ “ “ “ PI. 5, fig. 11. 
Shell obliquely and transversely ovate; height more than seven-eighths of the 
length, produced behind. Pallial margins regularly rounded, becoming more 
