LAMELLIB RANCHI A TA. 
151 
Ptychqpteria Vanuxemi, n. sp. 
PLATE LXXXV, FIG. 36. 
Shell large, sub-triangular; body narrow-elongate, sub-cylindrical, oblique at 
an angle of nearly 30° with the hinge-line; ventral margin very long and 
gently curving; posterior margin abruptly and acutely recurved. 
Left valve very convex along the axis of the body. Right 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, lamel- 
lose concentric striae. The concentric striae are crowded and somewhat 
fasciculate on the posterior and the wing, giving an undulated 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. 
Interior unknown. 
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 Chemung group at 
Warren, Pa. 
