LAMELLIBRa I N( II I ATA. 1 :; I 



A large specimen of the left valve has a Length of -)\ nun., height in mm., 

 and hinge-line 25 mm. A smaller one has a length of 24 mm., heighl L3 

 mm., hinge-line 20 mm. 



This species has a narrower anterior end than the preceding, a larger and 

 more extended wing, finer and undulating stria'. 



Formation and localities. In sandstones of the Upper Ghemung group, Smeth- 

 port, McKean comity, and at Warren. Warren count)'. Pa., associated with 

 Spirifera Verneuili. 



Ptychopteria Salamanca. 



PLATE XXIII. He.-, it 20. 



Ptychopteria Salamanca, Hall. Pal. N. V., vol. v. pt. 1. Plates and Explanations: PI. 23, figs. 17-20. 



Jan.. Ins.: 



Shell large, rhomboidal; body sub-ovate, oblique at an angle of about 40° with 

 the hinge-line: length more than once anil a half the height: ante-byssal 

 margin oblique, rounded below, slightly concave at the sinns, and sloping to 

 the broadly rounded base, thence abruptly recurved and continued almost 

 vertically into the margin of the wing. 



Valves convex, gibbous above the middle. The left valve is more gibbous 

 than the right ami somewhat larger. 



Hinge-line straight, length more than three-fourths the length of the shell. 



Beaks in front of the anterior third of the cardinal Hue, directed forward : 

 the left beak prominent, acute, arching over the hinge; the right beak obtuse, 

 depressed, scarcely rising above the hinge-line. Umbonal region gibbous, 

 subtending an acute angle. The umbo and beak of the left valve are much 

 more prominent, and the post-cardinal slope is obtusely sub-angular. 



Anterior end comparatively small, triangular, produced into an acute 

 extension. Wing large, triangular : margin gently concave ; extremity pro- 

 duced, acute. The fold and sulcus are more conspicuous in the right valve. 



Surface marked by fine, regular, undulating and interrupted radii, which 

 are more conspicuous on the wing: crossing these are regular concentric 



