20 PALJEONTOLOGY OF NEW YORK. 



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. 



AVICULOPECTEN ItTS. 



PLATE VII. FKi. 13. 



Arh-uhiprH, i Uys, Hall. Pal. N. V., vol. v. )it. 1. Plates and Explanations: PI. 7. fig. 13. Jan., 1883. 



Shell small, broadly ovate, length nearly ecpial 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 ornamenta- 

 tion : 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 striae of 

 growth. 



Interior characters unknown. Hinge margin apparently simple. 



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

 line L3 mm. 



This species is less oblique than A. [das, 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. cunceUatus (==A. Ihlleanus, 



