Lamellibranchiata. 233 



the ears, where the sides of the shell are nearly straight. Eight 

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

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

 straight, length three-fourths the length of the shell, not extending 

 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 sinus, and from the sides of the 

 umbo by a sulcus ; the byssal sinus is deep and rounded. 



Test marked by fine, alternating, filiform radiating striae, which are 

 absent on the ears, except as two or three alternating undulations. 

 Fine lines of growth mark the test and extend over the ears. Liga- 

 mental area linear and marked by an inflection of the hinge-margin. 



The specimen has a height of 15 mm. and a length of 13 mm., 

 hinge-line 10 mm. About 13 rays occupy the space of 5 mm., meas- 

 ured near the basal margin. 



This form may be distinguished by its equilateral proportions, acute 

 straight apex, the non-obliquity of the transverse axis to the hinge- 

 line, the broad, triangular ears and the alternating surface striae. 

 These characters separate it from A. striatus, to which it is most 

 nearly allied. 



Formation and locality. In sandstone of the conglomerate, associ- 

 ated with the upper Chemung group, at Salamanca, Cattaraugus 

 county, N. Y. 



AVICULOPECTEtf PATULUS. 



Aviculopecten patulus, Hall. Pal. N. T., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 9, figs. 32, 33. Jan., 1883. 



Shell large, longitudinally broadly elliptical ; height about five-sixths 

 as great as the length. The axis of greatest height is at right 

 angles to the hinge, and the line of greatest length is parallel to the 

 hinge and across the middle of the shell. Basal margin convex, 

 somewhat flattened in the middle. Lateral margins very full, and 

 curving rapidly to the ears. Valves convex, the convexity equal to 

 one-fourth the length of the hinge-line. The right and left valves 

 do not differ conspicuously in character, so far as observed. Hinge- 

 line apparently straight, equaling nearly two-thirds the length of 

 the shell, central, not extending as far as either lateral margin. 

 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 

 [Sen. Doc. No. 38.] 30 



