LAMELLIBRANCHIA TA. 
141 
This species has some resemblance to P. alata in the left valve, but its height 
is comparatively greater, the wing more truncate, and not produced at the 
extremity. 
Formation and locality. In a shaly sandstone above a conglomerate in the 
upper part of the Chemung group at Panama, Chautauqua county, N. Y. 
Ptychopteria elongata, n. sp. 
PLATE LXXXV, FIGS. 10-13. 
Shell of medium size, sub-rhomboidal, elongate; body sub-cylindrical, 
oblique at an angle of 30° with the hinge-line; length more than one-third 
greater than the height; anterior margin oblique, curving into the basal 
margin, with a slight concavity for the byssal sinus; posterior margin 
abruptly rounded. 
Left valve regularly convex below, gibbous above. Right valve somewhat 
depressed-convex. 
Hinge-line straight, about one-fifth less than the length of the valve. 
Beaks near the anterior fourth of the hinge, directed forward; left beak 
prominent, sub-acute, arching over the cardinal line; beak of right valve 
depressed, obtuse, scarcely rising above the hinge-line. Umbo gibbous in 
the left valve; the greatest convexity of the valve is about one-third the 
length from the beak. Umbonal angle acute. 
Anterior end short, produced and acute at the extremity, limited by a 
distinct oblique byssal depression. Wing narrow-triangular, joining the body 
of the shell near the posterior extremity, limited by a furrow which is not 
conspicuous in the lower part, but in the right valve is more marked; margin 
obliquely truncate. 
Surface marked by fine radii, which are distinctly cancellated by the con¬ 
centric striae, when the specimen is tolerably well-preserved; also by concen¬ 
tric lines of growth which, at somewhat regular intervals, are sharply elevated. 
The radii are obsolete on the anterior of the valve, and the concentric striae 
are lamellose. 
