LAMELLIBRANCHIATA. 97 



This species somewhat resembles P.jlabella; and differs in its less convexity, 

 more numerous strong rays with finer intermediate lines, and loss conspicuous 

 concentric striae. 



Formation and locality. In sandstone of the Chemung group at Chemung 

 Narrows, Chemung county, N. Y. 



Pterinea dispanda. 



PLATE XV, PIG. 7. 

 Pterinea dispanda, Hall. Pul. N. V.. vol. v. pt. 1. Plates anil Explanations: PI. 15, fig. 7. .Ian.. 1883. 



Shell large; body very broadly ovate, nearly erect: length greater than the 

 height; anterior margin very convex ; basal margin flattened, not produced 



posterior^. 



Left valve regularly convex, and only moderately gibbous on the umbo. 

 Right valve unknown. 



Hinge-line straight, greater than the length of the body, extended pos- 

 teriorly beyond the margin of the valve. 



Beak anterior, nearly rectangular, prominent, directed forward. Umbonal 

 region ample. 



Ear small, separated from the body of the shell by a broad undefined sul- 

 cus, which is marked by several oblique folds. Byssal sinus deep and abrupt. 

 Wing very large, depressed-convex, broad-triangular; defined l>y the retral 

 curving of the concentric stria?; concave on the margin: extremity 

 extremely produced and acute. 



Test ornamented with strong, unequal, rounded radii, which are sonic- 

 times bifurcating on the anterior portion. The wing is marked with similar 

 smaller rays which are sometimes fasciculate. Entire surface also marked 

 by concentric lamellose striae, which at irregular intervals arc crowded into 

 fascicles, giving an undulating aspect to the surface, and a low nodose 

 appearance to the stronger rays. 



Interior unknown. 



The specimen described has a height of 70 nun., length about 80 nun., and 

 the length of the hinge-line about 90 mm. 

 13 



