Lamellibranchiata. 275 



margin of the valve. Beak obtuse, rounded, scarcely directed for- 

 ward, prominent, anterior to the middle. Umbonal region wide, 

 indistinctly denned on the posterior side, more distinctly limited 

 anteriorly, subtending an angle somewhat greater than 90°. Ears 

 triangular, flat. Posterior ear five times as large as the anterior, 

 undefined; margin straight or slightly concave ; extremity abruptly 

 acute. Anterior ear small ; margin deeply concave from the byssal 

 sinus ; defined by a distinct sulcus ; extremity acute. 



Test apparently thick, marked by about fifty strong rounded rays 

 which are simple or bifurcating, always with finer intermediate rays. 

 Concentric striae strong, elevated, conspicuously crenulating the 

 radii. The radii mark the ears, and on the posterior ear are simple 

 and distant. 



Two specimens give about the following respective dimensions: 

 length 56, 57 mm., height 47, 53 mm., and length of hinge-line 52 

 and 46 mm. 



This species differs from P. suborbicularis in being more inequilate- 

 ral, with longer hinge, and less stronger and frequent radii. It dif- 

 fers from P. JVeptunus, by its more erect form, extended hinge-line, 

 distant and elevated radii, with stronger and more elevated concentric 

 striaa. 



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

 Angelica and Conewango, N. Y., and at Mansfield, Tioga county, Pa. 



Pterin"opecti:n Neptu^its. 



Pterinopecten JVeptunus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 8, figs. 5-7. Jan., 1883. 



Shell large, sub-orbicular, moderately oblique (more so in young 

 shells ) ; length one-fifth greater than the height ; pallial margins 

 regularly rounded, becoming extended posteriorly. Valves mode- 

 rately and nearly equally convex; very similar in form and surface 

 markings. Hinge-line straight, length less than the length of the 

 shell, situated anteriorly as regards the body of the valve. Beaks 

 obtuse, rounded, directed slightly forward, nearly erect, not promi- 

 nent. Umbonal region wide and undefined posteriorly, subtending 

 a very obtuse angle. Posterior ear much the larger, slightly con- 

 cave on the margin; extremity angular. Anterior ear small, 

 separated from the body of the shell by a sulcus ; margin convex, 

 extending obliquely outward from the byssal sinus; extremity 

 acute. 



