NAPLES FAUNA IN WESTERN NEW YORK, PART 2 253 



Pterochaenia sinuosa sp. nov. 



Plate 5, fig. 17-22 



Shell comparatively large ; beak attenuate, narrow and erect ; surface 

 strongly convex or rotund medially, with a broad and low radial sinus near 

 the anterior margin. Outline suborbicular, varying to obliquely oval ; 

 regular on the posterior and lower edges but rendered sinuous anteriorly 

 by the emergence of the sinus. Byssal margin short, very oblique, slightly 

 incurved and making a large angle with the vertical axis of the shell. The 

 byssal extensions are very broad, wing-shaped, and convex near the beaks, 

 narrowing rapidly downward ; sical grooves deep and narrow at the bottom, 

 broad at the top. Exterior smooth, showing only concentric growth lines ; 

 radial lines appear on exfoliated surfaces. 



This species is readily distinguished from P. fragilis and its vari- 

 ants by its large size, sinused surface, undulated outline and highly 

 developed sicae. An average specimen has a hight of 10 mm, length of 

 12 mm, and the byssal margin is 6 mm in length. 



Habitat. Genesee province ; Naples subprovince. This shell occurs 

 often in great numbers in the Styliola (Genundewa) limestone on Canan- 

 daigua lake, and at Middlesex, Yates co. It is also occasionally found in 

 the Genesee shales, and Professor Hall has represented such a shell from 

 these shales near Penn Yan N. Y. 1 



Pterochaenia perissa sp. nov. 



Plate 4, fig. 19 



This rare species presents the appearance of a P. fragilis nearly 

 halved by the byssal groove and bearing an extravagant flange. The 

 byssal groove extends over the greatest diameter of the shell, and the 

 flange itself is very wide, its width being one third the greatest length of 

 the shell ; it tapers very slowly from the beak outward. The surface of the 

 valve is concentrically lined ; on the flanges these striae become parallel 

 to its outer edge and are strongly marked. The ridge in the byssal groove 

 is conspicuous. 



Paleontology of New York, v. 5, pt 1, pi. 71, fig. 13. 



