LAMELLIBRANCHIA TA. 
19 
Interior characters not known. 
The original of this species is 20 mm. in height, 19 mm. in longitudinal 
diameter, and the length of hinge-line 12 mm. Another specimen is 14 
mm. in height and 12 mm. in length. 
This species is distinguished from A. duplicatus and A. rugcestriatus by the 
less rugose surface, smaller size and different outline. The form of the ears 
and byssal sinus is very similar to A. duplicatus, but differs in the regular 
reticulate surface; that species is also a comparatively longer shell. It is in 
shape more like A. rugcestriatus. 
Formation and localities. In the middle members of the Chemung group, 
at Philipsburgh and Rockville, Alleghany county; Conewango, Cattaraugus 
county; and near Westfield, Chautauqua county, N. Y. 
AviCULOPECTEN iEQUILATEKALIS, n. Sp. 
PLATE LXXXXI, PIG. 1. 
Shell of medium size, transversely ovate, erect, equilateral; height equal to 
the length; lateral and basal margins regularly rounded; upper anterior 
and posterior margins extending in nearly a straight line to the beak. 
Left valve slightly convex; greatest convexity on the umbo. 
Hinge-line straight, nearly two-thirds the length of the shell, situated 
centrally. 
Beak well-defined, situated near the .centre of the hinge-line. 
Ears sub-equal, triangular, defined from the umbo by a sinus in the margin, 
with a sulcus extending to the beak; margins slightly convex; extremities 
rounded. 
Test ornamented with about sixty regular, straight, alternating rays, 
crossed by fine, irregular strirn of growth. The rays are present on the ears, 
and are more numerous on the anterior ear. 
The specimen described has a length and height of about 38 mm., and 
hinge-line of 22 mm. 
