LAMELLIBRANCHIA TA. 
105 
Ptekinea (Vertumnia) avis. 
PLATE XXIV, FIGS. 9, 11, 13. 
Ptei'inea reversa, var. avis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PL 24, figs. 9, 11, 
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, flat 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 mm., 
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. reversa , 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 striae, 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 
