Lamellibranchiata. 329 







Surface marked by fine radiating striae which become finer on the 

 wing and anterior end ; and by striae of growth which are some- 

 what lamellose on the anterior of the shell. 



A left valve of this species has a length of 13 mm., height 10 mm., 

 hinge-line 11 mm. 



This species differs from P. giobosa in its shorter, truncate anterior 

 end, and stronger fold on the wing, which is comparatively stronger 

 than in any species yet observed. 



Formation and locality. In the sandstones of the Upper Chemung 

 group, Warren county, Pa. 



Ptychopteria Vanuxemi. 



PtycJwpteria Vanuxemi, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell large, sub-triangular ; body narrow-elongate, sub-cylindrical, 

 oblique at an angle of nearly 30° with the hinge-line ; ventral mar- 

 gin very long and gently curving ; posterior margin abruptly and 

 acutely recurved. Left valve very convex along the axis of the 

 body. Eight valve unknown. Hinge-line straight, length more 

 than one-fourth greater than the height, or about two-thirds the 

 entire length of the shell. Umbonal angle very acute. Anterior 

 end unknown. Wing very large, triangular, joining the body near 

 the posterior end ; the furrow and fold obscure ; margin obliquely 

 truncate to near the hinge, where it is concave and abruptly recurved 

 into the produced extremity. 



Test thin, marked by strong radii, and by fine, sharp, equidistant, 

 lamellose concentric striae. The concentric striae are crowded and 

 somewhat fasciculate on the posterior and the wing, giving an un- 

 dulated or imbricated appearance. The rays are very strong over 

 the middle of the body, and subdued on the wing and basal side, 

 and are distinctly crenulated by the elevated concentric lines, with 

 the interspaces cancellated. 



The specimen described, has a length of 70 mm., height 34 mm., 

 and hinge-line about 44 mm. 



This species is conspicuously distinct from any other ; in outline 

 it approaches some of the extreme forms of Pteronites. 



Formation and locality. In the highest beds of the Upper Che- 

 mung group at Warren, Pa. 



[Sen. Doc. No. 38.] 42 



