LAMELLIBRANCHIA TA. L05 



Pterixea (Vertumxia) avis. 



PLATE XXIV. FIGS. 9, 11, IS. 



Ptermea reoersa, var. avis, Hall. Pal. N. V.. vol. v. pt. 1. Plates an. I Explanations: PI. '-'4. figs. 9, II. 



13. Jan.. 1883. 



Shell of medium to large size, rhomboidal, oblique ; body ovate; Length greater 

 than the height; margin moderately rounded in front, becoming full on the 

 posterior side. 



Left valve depressed-convex above, flat or concave below. Right valve 

 convex; the greatest convexity about the middle of the valve. 



Hinge-line straight, length greater than the length of the shell, extended 

 anteriorly beyond the margin of the valve. 



Beak low. obtuse, inclined forward, situated on the anterior third of the 

 hinge-line. 



Cardinal expansions unequal, triangular, flat; margins concave; extremities 

 mucronate. Ear limited by a broad, shallow sulcus extending from the beak 

 to the rounded byssal sinus. Wing large, undefined. 



Surface of both valves marked by about twenty-five strong, rounded, equal 

 rays, reaching from the umbo to the base, with broad, Hat interspaces which 

 occasionally show a single fine intermediate ray. The same surface 

 characters extend over both cardinal expansions. The entire surface is 

 marked by fine, regular, sharp, continuous, concentric striae. 



Internal characters unknown. 



A left valve, illustrated on plate xxiv, fig. 13, has a length of 44 nun., 

 height 31 mm., hinge-line 49 mm. A large right valve has a height of 

 45 mm., length 65 mm., and hinge-line about 65 mm. 



This species resembles P. reverse/., but differs in its comparatively greater 

 obliquity, more extended hinge, and proportionally greater length. It differs 

 from P. prora in the flatness of the left valve, the strong rays, the sharp 

 elevated stria', and the convexity of the right valve. 



Formation and locality. In the Chemung group at Buck's quarry, near Elmira, 

 Chemung county, N. Y. 

 14 



