LAMELLIBRANCHIATA. II.; 



Interior unknown. 



A left valve has a length of 26 mm., height IS nun., and binge-lin'e 20 mm. 

 Another specimen has a length of 24 nun., heighl I I mm., and binge-line 

 17 nun. 



Compared with P. Eucrate and P. elongala, the body of the shell is compara- 

 tively shorter, the furrow of the wing more distinct, the byssal depression 

 shallower and more nearly vertical. Tt has the obscure angularity of P. Eucrate, 

 with coarser and more nearly vertical radii. 



Formation and locality. In the lower beds of the Upper Division of the 

 Chemung group, as seen at Warren, Pa. 



Ptychopteria Beecheri, n. sp. 



PLATE I. XXXV. FIGS 21, 11 



Shell large, rhomboidal ; body cylindrical, very arcuate in the hit valve, oblique 

 at an angle of about 40° with the hinge; length nearly twice the height ; 

 ante-byssal margin slightly oblique, curving gently into the sinus: ventral 

 margin broadly rounded, straighter toward the posterior end, which is 

 acutely recurved. 



Left valve ventricose, the greatest convexity a little above the middle; 

 abruptly rounded or sub-angular along the post-cardinal slope, and the eleva- 

 tion is continued into the angular posterior extremity. Right valve much 

 less convex. 



Hinge-line straight, length more than two-thirds the length of the shell. 



Beaks at about the anterior third of the hinge-line, very prominent and 

 incurved over the hinge in the left valve. In the right valve the beak is 

 subdued, not rising above the hinge-line. Umbo vciy gibbous in the left 

 valve, subtending an acute angle. 



Anterior end moderately large, limited by a very broad, shallow, slightly 

 oblique byssal depression : extremity flattened, acute, defined by an oblique 

 constriction in the margin just below the cardinal Line. Wing of medium 

 size, joining the body of the shell a little above the posterior extremit} ; 



