LAMELLIBRANCHIATA. 151 



PtYCIIOPTEIUA VaNUXEMI, 11. (Sp. 

 PLATE I.XXXV, FIG. 36. 



Shell large, sub-triaiiguhir ; 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, laniel- 

 lose concentric striai. The concentric strisB 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. 



