244 Thirty-fifth Report osr the State Museum. 



terior margin full, abruptly sloping to the beak. Left valve strongly 

 convex. Eight valve not observed. Hinge-line straight, equal to 

 the greatest length of the shell, extended anteriorly. Beak obtuse- 

 angular, directed forward, nearly central. Umbo deep, sides subtend- 

 ing an obtuse angle, sloping to the ears. Ears sub-equal. Anterior 

 ear narrow-triangular, elongate, acuminate, defined by the deep 

 byssal sinus and marked sulcus; margin concave. Posterior ear 

 wider, limited by an undefined sulcus ; margin concave; extremity 

 acute. 



Test ornamented by rounded radii, which bifurcate toward the 

 margin; crossed by prominent,, regular, concentric striae. Hinge- 

 area simple. 



The specimen has a length of 16 mm., height 15 mm., hinge-line 

 16 mm. 



This species differs from A. insignis, A. beUus&nd A. omatus in the 

 following characters: the anterior ear is narrower, the outline of the 

 shell is less oblique, and the form is more rotund. 



Formation and locality. In calcareous shales of the Hamilton group 

 at Dresden, Yates county, N. Y. 



Aviculopecten tenuis. 



Aviculopecten tenuis, Hall. Pal. N. Y.. vol. v, pt. 1. Plates and Explanations : 

 PI. 7, figs. 27, 28. Jan., 1883. 



Shell small to medium size, sub-orbicular, transverse axis oblique; 

 length and height equal ; margins regularly rounded, somewhat ex- 

 tended behind. Left valve slightly convex, nearly flat. Right valve 

 unknown. Hinge-line straight, nearly central ; length five-sixths of 

 the longitudinal diameter. Beak directed forward, not rising above 

 nor extending beyond the hinge, anterior to the center of the hinge- 

 line and of the valve. Umbonal angle 90°. Ears large, broad-trian- 

 gular, unequal, separated from the sides of the umbo by a broad, 

 shallow sulcus. Anterior ear about one-half the size of the posterior, 

 flat, margin convex ; extremity obtuse-angular. Byssal sinus broad 

 and comparatively shallow. Posterior ear marked by a low, convex 

 undulation, adjacent and parallel to the sulcus ; margin straight or 

 slightly concave ; extremity rectangular, pointed, more obtuse in 

 mature specimens. 



Test marked by about twenty -five strong, regular radii, with broader 

 concave interspaces, and also, in well-preserved specimens, smaller 

 intermediate rays. The specimens described are casts of the interior, 

 and show but faint traces of concentric lines of growth. The ears 



