LAMELLIBRANCHIA TA. 
9 
dued striae. The anterior ear is well-defined by the sulcus extending from 
the angular byssal sinus. 
Test ornamented by about forty strong, sharp, continuous rays, alternating 
in size with broader and concave interspaces, crossed by fine, sharp, crenu- 
lating concentric striae. The ears show finer concentric striae and a few rays. 
Pallial line impressed, continuous, extending parallel to the margin of the 
shell about half way from the beak, terminating near the centre of the 
posterior side, in a sub-circular, muscular impression, marked with regular 
concentric striae. The cast preserves traces of the exterior markings, but 
presents no definite characters of the hinge. 
The largest specimen has a height of 35 mm. A medium-sized specimen 
has a height of 26 mm.; length 27 mm.; hinge-line 24 mm. 
This species differs from the young of A. princeps, in its more acute beak, 
smaller anterior ears, and in having rays on both ears; the rays on the body 
of the shell are also stronger. It resembles A. formio in outline, but has more 
sharply elevated rays, and less strong concentric striae. A. pedeniformis has 
obtuse rounded beaks, and ears not marked by rays, which are distinguishing 
features of that species. 
Formation and localities. In the shales of the Hamilton group, Monteith’s 
Point, Ontario county; and Hamburg, Erie county, N. Y. 
Aviculopecten formio. 
PLATE V, FIGS. 20, 21. 
Aviculopecten formio, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 5, figs. 20, 21. 
Jan., 1883. 
Shell of medium size, obliquely ovate, extended behind; length equal to or 
somewhat less than the height. 
Yalves depressed, slightly convex. The right and left valves are very 
similar; the right being somewhat less convex, and having finer surface 
markings. 
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