34 
PALAEONTOLOGY OF NEW YORK. 
over the centre of the valve, becoming obscure toward the margins. The 
ears show the concentric striae only. 
The characters of the interior are not known. 
A specimen of the left valve measures 25 mm. in height, 29 mm. in length, 
and the hinge-line 21 mm. 
This species in general expression resembles A. tenuis, but is distinct in its 
smaller anterior ear, more obtuse beak, orbicular form, and more irregular and 
stronger rays. Their geological positions are widely separated. 
Formation and locality. In soft shaly beds of the Corniferous limestone, which 
constitute the upper portion of the group, at Lapham’s mill, near Victor, 
Ontario county, N. Y. 
Aviculopecten insignis. 
PLATE I, PIG. 8 ; PLATE III, PIG. 13 ; AND PLATE LXXXI, FIG. 7. 
Auiculopeclen insignis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 1, fig-. 8 ; pi. 8, fig. 13. 
Jan., 1883. 
Shell less than medium size, sub-rhomboidal, moderately oblique, about one- 
third longer than high ; basal margins rounded; anterior and posterior mar¬ 
gins obtusely angular or abruptly rounded, and extending along the cardinal 
slopes in a direct line to the beak. 
Both valves are quite convex; right valve somewhat the less convex. 
Hinge-line straight, nearly equal to the length of the shell. 
Beak obtuse-angular, prominent, directed forward, nearly central. Umbonal 
region ample, the sides subtending an obtuse angle, and sloping more 
abruptly to the anterior than to the posterior margin. 
Ears sub-equal, triangular. Anterior ear concave or flat, defined by a dis¬ 
tinct sulcus; margin deeply concave; extremity acuminate. Byssal sinus 
deep and well-marked. Posterior ear flattened, defined by the absence of 
the stronger radii; extremity slightly acute; margin concave. 
Test thin, marked by strong radiating costae, which in the left valve are 
abruptly elevated and increase by interstitial addition; crossed by infrequent 
