LAMELLIBRANCHIATA. 35 



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

 nodose character to the radii, and by finer lines of growth. Tlie right valve 

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

 crossed by fine concentric lines of growth. The radiating stria3 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. hellus and A. ornatus. The surface markings are very 

 similar to the former, but cpiite 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, (I, 9; AND PLATE LXXXI, FIG. 8. 



Avicida heUa, Conrad. Annual Geolog. Rop. N. Y., i>. .")4. 1841. 



Avimlopeeteii hdtus (Conrad), Hall. Pal. N. V., \-<il. v, pt. 1. Plates and Explanations: PI. 2, Hgs. 5, 



1), St. 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. 



