LAMELLIBRANCHIATA. 23 



Ligamental ai'ea narrow, well-marked, its width is .5 mm. in a specimen of 

 20 mm. in height. 



The oi'iginal specimen of this species is 20 mm. in height, 18 mm. in 

 length, and the hinge-line 13 mm. Another specimen is 13 mm. in height, 

 11 mm. in length, hinge-line 8 mm. The largest specimen found has a 

 height of 22 mm. 



This species resembles A. celsus more nearly than any other form here 

 described ; it differs from that one by its much smaller ears with concave 

 margins, more obtuse umbo, regular, equal striae, and comparatively shorter 

 form. The two species agree in the non-obliquity of the body of the shell to 

 the hinge-line. This species has a vertical range from the middle to the upper 

 members of the Chemung group, but is not abundant. 



Formation and localities. In the Chemung group at Painted Post, Steuben 

 county ; Chemung Narrows, Tioga county, N. Y. ; and in Bradford, Tioga and 

 Warren counties, Pennsylvania. 



AviCULOPECTEN CELSUS. 



PLATE Vn, FIUS. -29, 30. 



Amciihipectcit altux. Hall. Pal. N. Y., vol. v, pt. I. Plates and ExplanatiuiKS : PI. 7, tigs. 29, 30. 



Jan., 1883. 

 Not Apiculoptcteii altii-s. White. Bull. U. S. Geol. Surv.. vol. v, p. 110. 1879. 



Shell small, ovate cuneiform, sub-equilateral, not oblique; height one-fifth 

 greater than the length ; pallial margin rounded to near the ears, where the 

 sides of the shell are nearly straight. 



Right valve convex ; the greatest convexity being equal to one-fourth the 

 length of the hinge-line. Left valve not observed. 



Hinge-line straight, length tliree-fourths the length of the shell, not extend- 

 ing as far as either lateral margin. 



Beak acute, straight, extremity pointed, arching over the hinge-line ; umbo 

 prominent, subtending an angle of 80°. 



Ears broad-triangular, large, flat, sub-equal, the margins slightly convex ; 

 extremities rectangular ; separated from the body of the shell by a moderate 



