LAMELLIBRANCHIA TA. 
33 
Test thin, marked by fine sharp radii, with wider interspaces, which show 
one, two or three finer rays, crossed by fine crenulating lines of growth. 
The same characters of marking extend over the ears. 
Internal characters not known. 
The specimen is 14 mm. in length, 12 mm. in height, with hinge-line 
15 mm. 
This species, in surface markings, bears a slight resemblance to a young 
individual of Aviculopecten princeps; but the undefined ears and proportionally 
longer hinge-line distinguish it. 
Formation and locality. In the upper layers of the Corniferous limestone; 
Young’s farm, Williamsville, Erie county, N. Y. 
Section b. 
Aviculopecten ignotus. 
PLATE I, FIG. 2. 
Aviculopecten ignotus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 1, fig - . 2. Jan., 1883. 
Shell of medium size, transversely and obliquely sub-ovate; height about five- 
sixths of the length; margins regularly rounded, full on the anterior and 
posterior sides. 
Left valve slightly convex, nearly flat. Right valve unknown. 
Hinge-line straight, central, length nearly equal to the height of the valve. 
Beak obtuse, rounded, low, directed toward the anterior. 
Posterior ear large, broad-triangular, separated from the side of the umbo 
by a wide shallow sulcus; margin slightly concave; extremity obtuse- 
angled. Anterior ear less than one-half the width of the posterior, narrow- 
triangular, separated from the umbo by a deep byssal sinus and a distinct 
sulcus, extending to the apex of the beak; margin convex; extremity 
rounded. 
Test thin, about .5 mm. in thickness; marked with about twenty-five 
irregular, rounded radii, which are crossed by very fine concentric striae, and 
occasionally interrupted by varices of growth. The rays are conspicuous 
5 
