130 PALjEONrOLOGY OF NEW YORK. 



two species are distinguished from tlic tonus wliicli follow by the large anterior 

 end \\ liirh is separated from the body liy a l)road byssal depression. 



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

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

 prol)ablv of the I'pper Chemung group; Smethport, McKean county, Pa. 



Ptv<"H(>i'ti:i!1a sinuos.v. 



PLATE XXIII, FIG. 13; PLATE LXXXV, FIG 8. 

 Plychoplerla xinuosa. Hai.l. Pal. N. Y., vol. \-. pt. 2. PlatHs smd Explanations: PI. 23, fig. l."?. .laii., 1S83. 



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

 about 40'^ witli tlic hinge; length more than one-third greater than the 

 height: ant('-l)yssal margin nearly vertical, curving into the broad sinus; 

 base broadly rounded ; posterior margin recurving into the wing. 



Left valve convex Ixdow, gibbous in the middle ami al)ove. l\ight valve 

 unknown. 



Ilinge-line straight, length four-fifths the length of the shell. 



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

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

 body on tiie posterior side, and by the byssal depression on the anterior side. 

 Umbonal angle about 30". 



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

 vertical byssal depression; extremity angular, ^^'ing narrow-triangular, 

 extending nearly to the posterior extremity of the liody : margin nearly 

 vertical, slightly concave ; extremity somewhat produced, angular. 



Surfiice marked by fine imdulating radii, whicli aiv less conspicuous on the 

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

 imbricating lainella\ On the anterior side of the body the rays are cancel- 

 lated by tiie elevated concentric striae. 



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

 of its length posterior to tiie beak, and a narrow cai'dinal tooth anterior to the 

 l>i'ak and parallel in tbc binge. 



