LAMELLIBRANCJIIA TA. 
147 
Ptychopteria perlata, n, sp. 
PLATE LXXXV, FIGS. 38, 39. 
Shell large, rhomboidal; body ovate, oblique; length' one-sixth greater than 
the height; anterior and basal margins broadly curved; posterior end angular. 
Left valve very convex, gibbous above. Right valve somewhat gibbous 
above, having a convexity of about one-half that of the left valve. 
Hinge-line straight, nearly equal to the length of the shell. 
Beak at about the anterior third of the cardinal line, prominent and 
arching over the hinge in the left valve. Umbo gibbous in the left valve 
and convex in the right, subtending an acute angle. 
Anterior end large, obscurely defined by a shallow byssal depression, which 
is obsolete in the right valve; margin convex; extremity acuminate. Wing 
broad triangular, joining the body at the posterior end; the furrow and fold 
are stronger in the left valve; margin slightly convex below, inclining a 
little forward ; extremity produced, acute-angular. 
Surface of the left valve marked by fine, close, rounded radii, which are 
often interrupted by the concentric lamellae. The radii are finer upon the 
wing, obsolete upon the anterior end, and scarcely present on the right valve. 
The concentric lines of growth and lamellae, give an irregularly undulating 
appearance to the surface. 
Interior unknown. 
A left valve has a length of 31 mm., height 26 mm., and hinge-line 30 mm. 
A right valve measures 33 mm. in length, 27 mm. in height, and hinge-line 
32 mm. 
This species is a shorter, more erect form than P. lata, and the left valve is 
more convex and broader below. 
Formation and locality. In the upper beds of the Chemung group at 
Warren, Pa. 
