98 
PALAEONTOLOGY OF NEW YORK. 
This shell bears some resemblance to the more extravagant forms of Pterinea 
jiabella , but it is larger than any known specimen of that species, with a propor¬ 
tionally longer and less defined body, and distinctly different surface ornamen¬ 
tation. 
Formation and locality. In the upper beds of the Chemung group at Mansfield, 
Tioga county, Penna. 
Pterinea Chemungensis. 
PLATE XVI, FIGS. 3, 7, 10, 12; PLATE LXXXIV, FIG. 21. 
Avicula Chemungensis, Conrad. Jour. Acad. Nat. Sci., Phila., vol. 8, p. 243. 1842. 
Avieula mectenifovmis, Hall. Geolog. Snrv. N. Y.: Rept. Fourth Dist., p. 262. 1843. 
Pterinea Chemungensis, (Conrad) Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 16, figs. 3, 
7, 10, 12. Jan., 1883. 
Shell very large, rhomboidal; body of shell ovate, narrower above, nearly 
erect, or sometimes oblique; length less than the height; greatest length 
below the middle; basal and post-basal margins rounded; the anterior 
margin above the middle is nearly straight, and the corresponding portion of 
the posterior margin is gently concave. 
Left valve moderately convex above, depressed-convex in the lower part. 
Right valve depressed-convex towards the beak, flat or slightly concave below. 
Hinge-line straight, central; length nearly or quite equal to the length of 
the shell. 
Beak anterior, acute, directed forward, arching a little over the hinge-line. 
Umbonal region not strongly defined, most prominent a little below the 
hinge; subtending an acute angle. 
Ear short, nearly equilateral, limited by a rounded sulcus; margin concave, 
with a marked sinuosity and arching of the shell for the byssal sinus. Wing- 
large, triangular, and extending beyond the posterior margin of the valve, not 
distinctly defined by a sulcus or by marked change in the surface characters 
from the body of the shell; margin straight or slightly concave; extremity 
obtuse. In the right valve, the wing is less distinctly defined than in the 
left. 
Test somewhat thin ; left valve marked by slender, filiform rays, variously 
