208 
PALAEONTOLOGY OF NEW YORK. 
Left valve moderately convex below, gibbous on the umbo. Right valve 
flat below, depressed-convex in the middle, and more convex above, propor¬ 
tionally wider than the left, and distinguished by its depressed-convex form. 
Hinge-line straight; length greater than the length of the valve. 
Beak of left valve sub-anterior, acute, directed forward, rising slightly 
above the hinge-line. Beak of right valve depressed, not rising above the 
cardinal line. Umbonal region of left valve moderately gibbous, subtending 
a very acute angle. 
Anterior end greatly extended, acute, rostrate, limited by a shallow byssal 
depression. Wing narrow-triangular, joining the body at the posterior 
extremity, defined by the recurving of the striae; margin'abruptly and 
symmetrically concave; extremity produced beyond the posterior limit of 
the shell. 
Test thin, marked by fine, sharp, closely arranged, concentric striae, which 
are sometimes fasciculate upon the body and anterior side, and very distinct 
upon the wing. Partial casts of the interior of the left valve give indications 
of fine radii which appear to belong to the intimate structure of the shell. 
Characters of the interior unknown. 
A left valve has a length of 32 mm., height 16 mm., and hinge-line 
37 mm. A right valve has a length of 34 mm., height 19 mm., and hinge¬ 
line 40 mm. 
This species is distinguished by the great length of the hinge-line, its narrow 
outline, and anterior extension. It approaches Pteronites in character, but 
differs in having a distinct wing, more depressed form, and a recurvation of 
the striae along the post-umbonal slope. 
Formation and localities. In the Chemung group, Philipsburg, Alleghany 
county, N. Y., and Kelly’s creek, Tioga county, Pa. 
