314 Thikty-fipth Report on the State Museum. 



Formation and localities. In sandstones of the Upper Chemung 

 group, Smethport, McKean county, and at Warren, Warren county, Pa., 

 associated with Spirifera Verneuili. 



Ptychopteria Salamanca. 



PtycTwpteria Salamanca, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 23, figs. 17-20. Jan., 1883. 



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

 40° with the hinge-line; length more than once and a half the height ; 

 ante-byssal margin oblique, rounded below, slightly concave at the 

 sinus, 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 and 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 line, directed 

 forward : the left beak prominent, acute, arching over the hinge ; 

 the right beak obtuse, depressed, scarcely rising above the hinge- 1 

 line. Umbonal region gibbous, subtending an acute angle. The 

 umbo and beak of the left valve are moeh more prominent, and the 

 post-cardinal slope is obtusely sub-angular. Anterior end compara- 

 tively small, triangular, produced into an acute extension. Wing 

 large, triangular; margin gently concave; extremity produced, 

 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 lines, which are irregularly crowded into sub-imbricating 

 lamellae. On the anterior end of the valve the radii are cancellated 

 by the concentric striae. Interior characters unknown, except a 

 narrow groove along the ligamental area. 



A left valve has a length of 41 mm., height 24 mm., hinge-line 

 32 mm. A similar right valve has a length of 40 mm., height 24 

 mm., hinge-line 34 mm. 



This species varies in different conditions of preservation. The 

 obtusely sub-angular appearance of the posterior slope is often exag- 

 gerated by lateral pressure or subdued by vertical pressure. The same 

 is true of the folds of the wing. In some conditions the radiations 

 are continuous, in others they are cancellated. In weathered speci- 

 mens the striae are sometimes nearly obsolete, and the concentric 

 lamellae more prominent. 



Formation and locality. In the Chemung group, in a sandstone 

 above the conglomerate at Rock City, near Salamanca, N. Y. 



