13(3 PALMONTOLOGY OF N FAV YORK. 



PtVCHOPTERIA FALCATA, 11. sp. 



I'L.VTE LXXXV, KIGS. 6, 7. 



SuELi, ol' inediuiu size, rhoiiiboidal, suh-ialcate ; hoch" narrow-ovate, ()lili(|iio at 

 an angle ofal)ont 45° with tlic eanlinal line ; leiiiitli one-tburth greater than 

 the licigiit : antcriiii- and l)asal margins liroadJN rounded: posterior margin 

 ahruptiv recurved. 



Lett valve convex, gihhous above, aicuatc. liiLdit valve convex on the 

 uinho, depressed-convex helow. 



Hinge-line straight, greater than the height of the shell. 



Beak situated at about the anterior fourth of tlie canlinal line, prominent 

 and arching over the liingc in tlic left valve; lu^t elevated in the right valve. 

 Umlto jibruptly gibbous in the left valve, snl)tending an acute angle. 



Anterior end liniiteil liv a sliallow. ncarlv \ertical byssal de])ression, which 

 iiudincs l)ackwaid in some specimens; margin convex; extremitv acuminate. 

 Wing triangular, joining the body near tiic ])osteii()r end ; margin straight, 

 slightly concave just hrlow the hingi'-linc ; extremity acute. 



Surface of both valves marked by fnie radiating stria', which are less 

 con.spicuous on the wing and obsolete on the anterior end ; and with 

 concentric striae, which are sometimes strongly lanudlose. jiroducing inidu- 

 lations of the surface. 



Interior unknown. 



A left valve has a length of 28 mm., heigiit 'I'l mm., hinge line 1^4 mm. 

 A similar right valve has a length of 28 mm., height 15 mm., and hinge-line 

 24 mm. 



The shell of this species is comparatively longer, the l)odv more oblique, and 

 the wing smaller than in P. Thclis. 



Formation and localitij. In a sandstoije and conglomerate of the Upper 

 Chemung group at Alleghany Springs, Warren county, Pa. 



