LAMELLIBRANCHIATA. 89 



Ckenipecten Winchelli. 



PLATE IX, FKiS. 1, 2, J, At-30. 



Aviculopecten Winchelli, Meek. Pal. of Ohio, vol. ii, p. 296, pi. 15, figs. 50, 58. L875. 



Crenipeeten (Pecteu) Winchelli (Meek), Hall. Pal. N. Y., vol. v. pt. 1. Plates and Explanations: PI. 9, 



figs. 1, .». 4. 25-30. Jan.. 1883. 



Shell larger than medium, nabelliform, equilateral, not oblique; length a little 

 greater than the height ; margins regularly rounded below. On the anterior 

 side, from a point two-thirds the height of the valve above the base, the 

 antero-cardinal margin extends in a direct line to the beak ; the posterior 

 side, from a point a little above the middle, also slopes in a direct line to the 

 beak. 



Left valve moderately convex ; the greatest convexity about one-third the 

 height of the shell from the beak. Right valve nearly Hat, depressed-convex 

 above. The right and left valves are unlike. 



Hinge-line straight, central, length about two-thirds the length of the 

 shell. In several specimens referred to the right valve, the length of the 

 hinge is nearly equal to the length of the valve. 



Beak of left valve acute, erect, prominent. Beak of right valve depressed, 

 obtuse, not rising above the hinge-line. Umbonal region of left valve dis- 

 tinctly defined, subtending a right angle. 



Ears of left valve triangular, defined by shallow but distinct sulci. Margin 

 of anterior ear convex, with a shallow sinus at the base. Posterior ear the 

 larger ; margin concave, with a comparatively broad sinus. The extremities 

 of the ears in the right valve are acute. Byssal sinus deeper and more 

 angular in the right valve. 



Surface of left valve marked by numerous rounded or sub-angular, alter- 

 nating rays, with somewhat wider interspaces, crossed by sharp, elevated, 

 concentric strife ; the ears show the same markings. Right valve marked 

 by obscure radii, which are stronger on the ears. 



Ligamental area with numerous narrow cartilage-pits. 



A large left valve has a length of 47 mm., height 42 mm., hingedine 29 

 12 



