LAMELLIBRANCHIA TA. 
35 
elevated thread-like concentric crenulating striae, which sometimes give a 
nodose character to the radii, and by finer lines of growth. The right valve 
is marked by rounded rays arranged in pairs, bifurcating on the umbo, 
crossed by fine concentric lines of growth. The radiating striae are obscure 
on the ears, being more strongly marked on the anterior one. 
The interior characters have not been observed. 
The largest specimen has a length of 27 mm., height 20 mm., hinge-line 
23 mm. A smaller specimen of 18 mm. in length has a hinge-line of precisely 
the same length. 
The specimen figured on plate 1 is a young individual and does not well 
show the characters of the species which are better seen on the other figures 
referred to. See plate 81, fig. 7. 
This species is less oblique, and the extremity of the posterior ear is less 
mucronate than in A. bellus and A. ornatus. The surface markings are very 
similar to the former, but quite distinct from the latter. 
Formations and localities. In limestone above the Marcellus shales, at Staf¬ 
ford, Genesee county; in the softer shales of the Hamilton group at Moscow, 
Livingston county; and at Hamburgh, Erie county, N. Y. 
Aviculopecten bellus. 
PLATE II, FIGS. 5, 6, 9; and PLATE LXXXI, FIG. 8. 
Avicula bella, Conrad. Annual Geolog. Rep. N. Y., p. 54. 1841. 
Aviculopecten bellus (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 2, figs. 5, 
6, 9. Jan., 1883. 
Shell small, longitudinally sub-elliptical; height equal to two-thirds or three- 
fourths of the length; margins regularly rounded. 
Valves moderately convex; the right valve somewhat shallower than the 
left; very similar in form and ornamentation. 
Hinge-line straight, the length a little greater than the longitudinal 
diameter of the shell, nearly central, extending equally beyond the posterior 
and anterior margins. 
