130 PALEONTOLOGY OF NEW YORK. 



two species axe distinguished from the forms which follow by the large anterior 

 end whirl: is separated from the body by a broad byssal depression. 



Formation and locality. In a coarse sandstone, from a bowlder containing the 

 same associated fossils as a sandstone at Portville, Cattaraugus Co., N. Y. ; 

 probably of the Cpper Chemung group; Smethport. McKean county. Pa. 



PtTCHOPTEEIA SIM iis \. 



PLATE XXIII. FIG. 13; 1M. ATI: I. XXXV. FIG 8. 



Ptyehopleria sinwosa, Hall. Pal. N. Y.. vol. v, [it. 2. Plates and Explanations : PI. 23, fig. 13. Jan.. 1883. 



Shell of medium size, rhomboidal ; body narrow-ovate, oblique at an angle of 

 about 40° with the hinge; length more than one-third greater than the 

 height; ante-byssal margin nearly vertical, curving into the broad sinus; 

 base broadly rounded ; posterior margin recurving into the wiug. 



Left valve convex below, gibbous in the middle and above. Right valve 

 unknown. 



Hinge-line straight, Length four-fifths the length of the shell. 



Beak at about the anterior third of the hinge, acute, directed forward. 

 Umbonal region strongly gibbous, limited by the abrupt depression of the 

 body on the posterior side, and by the bj^ssal depression on the anterior side. 

 Umbonal angle about 30°. 



Anterior end large, narrow, rounded, defined by a broad, shallow, nearly 

 vertical byssal depression; extremity angular. Wing narrow-triangular, 

 extending nearly to the posterior extremity of the body ; margin nearly 

 vertical, slightly concave; extremity somewhat produced, angular. 



Surface marked by fine undulating radii, which are less conspicuous on the 

 wing, and by fine concentric lines of growth, which are crowded into sub- 

 imbricating lamella'. On the anterior side of the body the rays are cancel- 

 lated by the elevated concentric striae. 



The ligamental area shows a sharp linear groove extending three-fourths 

 of its length posterior to the beak, and a narrow cardinal tooth anterior to the 

 beak and parallel to the hinge. 



