LAMELLIBRANCHIATA. 97 



This species somewhat resembles P.flabella; ;ind (lifters in its less convexity, 

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

 concentric strioe. 



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

 Narrows, Chemung county, N. Y. 



Pterinea dispanda. 



I'l.ATE XV, FIG. 7. 

 Ptennea d'l.ipanda. Hall. Pal. N. Y., vol. v, pt. 1. Plates ami E.Nplaiiations : PI. ]"), tii,'-. 7. Jan., 1SS3. 



Shell large ; body very In-oadly ovate, nearly erect ; length greater than the 

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

 posteriorly. 



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

 Right valve unknown. 



Hinge-line straight, greater than the length of the Ixxly, extended i)os- 

 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 ))y 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 by the retral 

 curving of the concentric strias ; concave on the margin ; extremity 

 extremely produced and acute. 



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

 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 are 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 7(t nun., length about 80 mm., and 

 the length of the hinge-line about 90 mm. 

 13 



