LAMELLIBRANCHIATA. 25 



Beaks obtuse, rounded; umbo prominent, straight, central, well-defined 

 by its gibbous form and the rapid slope of the sides. Umbonal angle 110°. 



Ears broad-triangular, sub-equal, separated from the body of the shell by 

 a broad, deep sinus; margins concave below, becoming convex above the 

 middle ; extremities rounded. 



Test ornamented by regular, sharp radii, with broader concave inter- 

 spaces, and some liner radii, crossed by irregular crenulating lines of growth. 

 Near the basal margin of a large specimen, there are five of these rays in 

 the space of 10 mm. A smaller specimen has eleven rays in the same 

 space. 



The interior is not preserved. 



The measurements of one individual are: height 55 mm., length 69 mm., 

 hinge-line 41 mm.; of another specimen, height 26 mm., and length 30 mm. 



This species nearly resembles in form A. elltpticus, and differs by its sharp, 

 crenulated radii, while that species is marked by strong, rounded, continuous 

 plications; and the hinge-line is comparatively somewhat longer. These two 

 forms differ from others in their broad longitudinally elliptical outlines, and 

 the amplitude of the umbones. 



Formation and locality. In conglomerate and sandstone, associated with the 

 Upper Chemung group, at Rock City, near Salamanca, ( 'attaraugus county. X. V. 



AVICULOPECTEN ELLIPTICUS. 



PLATE VII, PIG. 31. 



Avicvlopecten ellipticus, Hall. Pal. N. Y., viol, v, j>t. 1. Plates and Explanations: PI. 7. fig. 31. .Ian.. I 1 *'-:!. 



Shell large, longitudinally broadly elliptical, equilaterial, no! oblique; height 

 equal to about four-fifths of the length ; margins regularly convex and rapidly 

 curving to the beak. 



Left valve capacious, convex. Right valve not observed. 

 Hinge-line straight, central, length equal to about one-half the length of 

 the shell. 



Beak straight, central, obtuse, rounded; umbonal angle about 110°. 

 4 



