I.; I PALEONTOLOGY OF NEW YORK. 



margin broadly curved; posterior extremity abruptly or sub-angularly 

 recurved. 



Left valve convex, gibbous on the umbo and obtusely sub-angular along 

 the post-cardinal slope. Right valve less convex, somewhat smaller than the 

 left. 



Hinge-line straight; length about two-thirds the length of the valve. 



Beak near the anterior fourth of the Length of the hinge, directed forward ; 

 beak of left valve prominent, acute, incurved over the hinge-line; beak of 

 right valve obtuse, and not elevated. Umbonal region of the left valve 

 gibbous and angular, of the right valve convex, subtending a very acute 

 angle. 



Anterior end small: margin rounded; extremity acute. Byssal depression 

 oblique, directed backward. Wing narrow, triangular, joining the body at the 

 posterior end: margin obliquely truncate, scarcely concave; extremity 

 apparently not produced. 



Surface marked by fine radiating stria 1 , which are more conspicuous on the 

 holy of the valve and upon the wing, and are very obscure on the anterior 

 end: these are crossed by fine concentric stria' of growth which, at irregular 

 intervals, are raised into fascicles, usually more conspicuous on the umbo 

 and post-cardinal slope. On the right valve the radii are usually obsolete. 



Interior unknown, except the usual linear groove along the binge-line. 



A large left valve has a length of 40 mm., height 20 mm., and hinge-line 

 2S mm. Another is 08 mm. in length, height 20 mm., and hinge-line 27 mm. 



In this species the body is more oblique than in P. Salamanca ; the angularity 

 of the left valve is in a direct line down the middle of the body: the shell 

 is comparatively narrower ; the extremity of the wing is not produced: the 

 byssal depression is more oblique. The want of striae on the anterior end and 

 their obsolescence on thi' right valve are marked characters. It is proportionally 

 much longer than P. Sao, with which it is associated. 



Formation and locality. In the lower part of a conglomerate of the Chemung 

 group at Panama, Chautauqua count}-, N. Y. 



