LAMELLIB RANCHI A TA. 
97 
This species somewhat resembles P. jlabella; and differs in its less convexity, 
more numerous strong rays with finer intermediate lines, and less conspicuous 
concentric striae. 
Formation and locality. In sandstone of the Chemung group at Chemung 
Narrows, Chemung county, N. Y. 
Pterinea dispanda. 
PLATE XV, FIG. 7. 
Pterinea dispanda, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 15, fig. 7. Jan., 18S3. 
Shell large; body very broadly 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 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 by the retral 
curving of the concentric striae; 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 70 mm., length about 80 mm., and 
the length of the hinge-line about 90 mm. 
13 
