Lamellibranchiata. 281 



valve depressed-convex. Left valve unknown. Hinge-line short, 

 straight, anterior ; length about one-third the height of the valve. 

 Beak low, obtuse. Umbonal region not strongly defined, subtend- 

 ing an obtuse angle. Ears very small, nearly equal, bounded by 

 shallow sulci. Byssal sinus not distinct. 



Surface marked by numerous low, rounded radii, with wider inter- 

 spaces and smaller intermediate radii ; crossed by fine concentric 

 lines of growth, which are stronger and crowded on the ears, form- 

 ing their only surface marking. Interior unknown. Ligamental area 

 obscurely crenulate. 



The specimen described has a length of 18 mm., width 16 mm., 

 hinge-line 5 mm. 



This species resembles in form C. crenulatus, but differs in the 

 radii, and in the proportionally much shorter hinge-line. The surface 

 markings are similar to 0. liratus, but it is different in its proportions 

 of length and height. 



Formation and locality. In the shales of the Chemung group at 

 Philipsburg, Alleghany county, N. Y. 



Crenipecten liratus. 



Crenipecten liratus, Hall. Pal. N.Y., vol. v, pt. 1. Plates and Explanations : 

 PI. 9, fig. 24. Jan., 1883. 



Shell small, obliquely sub-ovate ; length a little less than the height ; 

 anterior and basal margins rounded ; post-basal margin produced, 

 and thence extending in a direct line to the beak. Left valve 

 moderately convex, the greatest convexity distant one- third the 

 height of the valve from the beak. Right valve unknown. Hinge- 

 line straight, short; length about one-third the height of the valve. 

 Beak acute, erect, a little anterior to the center of the shell, not 

 rising above the hinge. Umbonal region moderately elevated, sub- 

 tending an acute angle. Ears small, triangular, defined by moderate 

 sulci ; the posterior ear the larger. Byssal sinus not distinct. 



Surface marked by prominent, rounded, alternating radii, with 

 intermediate smaller ones. There are about six larger rays, six 

 smaller, and twice that number of still smaller intermediate 

 striae, all crossed by strong, regular, concentric laminae of growth. 

 The ears are apparently destitute of rays. The crenulations of the 

 ligamental area are small and obscure. 



The specimen described has a length of 20 mm., height 22 mm., 

 hinge-line 7 mm. 



[Sen. Doc. No. 38.J 36 



