230 Thibty-eifth Report on the State Museum. 



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 

 center 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 striae 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. 



This species is distinguished by its erect equilateral form, sub-equal 

 ears, and the strong, regularly alternating radii. 



Formation and locality. In the upper beds of the Chemung group 

 at Alleghany Sulphur Springs, Warren county, Pa. 



Ayiculopectest Itys. 



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

 PI. 7, fig. 13. Jan., 1883. 



Shell small, broadly ovate; length nearly equal to the height, slightly 

 oblique ; margins regularly rounded, nearly equilateral. Right valve 

 depressed-convex. Left valve not known. Hinge-line straight, 

 sub-central, having an extent of a little more than one-half the 

 greatest length of the shell. Beak acute, directed slightly forward. 

 Posterior umbonal slope making a greater angle with the hinge-line 

 than the anterior. Umbo subtending a right angle. Ears nearly 

 equal. Anterior ear the larger, obtuse at the extremity, marked by 

 several strong radii, separated from the umbonal region by a strong 

 sulcus. Posterior ear narrow, triangular, margin concave, separated 

 * by a distinct sinus from the body of the shell, with no rays of orna- 

 mentation ; obtuse-angular. Byssal sinus well-defined. 



Surface marked by sub-angular, rounded radii, which are regularly 

 increased in size with the growth of the shell, but rarely increased in 

 number by implantation ; concentrically marked by fine, regular, 

 thread-like strias of growth. 



The specimen described has a length of 25 mm., height 27 mm., 

 hinge-line 13 mm. 



This species is less oblique than A. Idas, the hinge-line shorter, 

 radii not present on the posterior ear, surface markings coarser and 

 rays increasing more rapidly in size though fewer in number. In 

 A. cancellatus ( = A. [Pecten] Hallianus, d'Orbigny), the valve is more 



