78 PALEONTOLOGY OF NEW YORK. 



Pterinopecten crenicostatus. 



PLATE VIII, FICiS. i, i; AND PLATE LXX.XII, FIG. 14. 



Pterinopecten crenvtatiu (by error)! Ball. Pal. N. Y.. vol. v. pt. 1. Plates and Explanations: PL 8. H^s. 



:i. 4. J;in.. 1883. 



Shell large, sub-orbicular, slightly oblique; length somewhat greater than the 

 height ; pallia] margins regularly curved, broadly rounded from the antero- 

 lateral tn the basal margin; post-lateral margin less convex. 



Lett valve very moderately convex. Right valve not known. 



Hinge-line straight, length one-fifth less than the length of the shell, 

 extended anteriorly, but not as far as the anterior margin of the valve. 



Beak obtuse, rounded, scarcely directed forward, prominent, anterior to 

 the middle. Umbonal region wide, indistinctly defined 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. 



Internal characters not known. 



The two specimens figured give about the following respective dimensions : 

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

 40 mm. 



This species differs from P. suborbkularis in being more inequilateral, with 

 longer hinge, and stronger ami less frequent radii. It differs from P. Neptunus, 

 pi. 8, fig. 6, by its more erect form, extended hinge-line, distant and elevated 

 radii, with stronger and more elevated concentric stria?. 



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

 Conewango, X. Y., and at Mansfield, Tioga county, Pa. 



