208 PALAEONTOLOGY OF NEW YORK. 



Left valve moderately convex below, gibbous ou the umbo. Right valve 

 Hat below. (lcpres.sed-coii\ox in the middle, and more convex above, propor- 

 tionally wider than the left, and distinguished by its depressed-convex ibrm. 



Hinge-line straiglit ; length greater than the length of the valve. 



Beak of left valve sub-ant€rior, acute, directed forward, rising sliglitlv 

 above the hinge-line. Beak of riglit valve depressed, not rising above the 

 cardinal line. I'liiboiial region of left valve moderately gibbous, snlitending 

 ii very acute angle. 



Antcriiir end greatly extended, a(!ute, rostrate, limited by a shallow b\ ssal 

 depression. Wing narrow-triangular, joining the body at tlic posterior 

 extremity, defined by the recurving of the stria>; margin abrupth- and 

 symmetrically concave; extremity produced beyond the posterioi- limit of 

 the shell. 



Test thill, iiiarkcil by fine, sharp, closely arraiigi'c I, concentric stria-, which 

 are sometimes fasciculate upon the body and anterior side, and very distinct 

 npon the wing. Partial casts of tlic interior of the left valve give indications 

 of fine radii wliich appear to Ijelong to the intimate structure of the shell. 



Characters of tlic interior unknown. 



A left valve has a length of >5'2 mm., height K! mm., and hiii<:c-line 

 il mm. A right valve has a length of .■J4 nun., hciglit I'.i nun., and liinge- 

 line 4(1 mm. 



This species is distinguished by tlie great lengtli of the liingr-line, its naiiow 

 outline, and anterior extension. It approaches Pteronites in character, but 

 differs in having a distinct wing, more depressed form, and a recurvation of 

 the strise along the po.st-uiiibnnal slope. 



Formation and localities. In the Chenumg gron|). I'liilipsburg, Alleghany 

 county, N. Y., and Kelly's creek, Tioga county, Pa. 



