LAMELLIBRANCHIATA. 35 



elevated thread-like concentric crenulating striae, which sometimes give a 

 nodose character to the radii, and by liner lines of growth. Therighl valve 

 is marked by rounded rays arranged in pairs, bifurcating on the umbo, 

 crossed by fine concentric lines of growth. The radiating stria' arc obscure 

 on the ears, being more strongly marked on the anterior one. 



The interior characters have not been observed. 



The largesl specimen has a Length of '11 mm., height 20 mm., hinge-line 

 23 mm. A smaller specimen of is 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 s|, 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. 



AVICULOPECTKN BELLUS. 

 PLATE II. PIGS .".. >': i. UJD PLATE l.\\\I, He - 



AvictUa bella, Conrad. Annual Geolog. Kip. N. V.. p. 54. 1841. 



Ariruh,ji,,ti :i bellim (Conrad), Hall. Pal. N. V.. vol, v. pt, 1. Plates and Explanations: PI. 2, figs. 6, 



6, '■>. Jan., l^.s. 



SHELL small, longitudinally sub-elliptical; beighl equal to two-thirds or three- 

 fourths of the length; margins regularly rounded. 



Valves i Lerateiy 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. 



