LAMELLIBRANCHIATA. 141 



This species lias some resemblance to P. alata in the left valve, Init its height 

 is comparatively greater, the wing more truncate, and not produced at the 

 extremity. 



Formation and locality. In a slialy sandstone above a conglomerate in the 

 upper part of the Chemung group at Panama, Chautauqua county, N. Y. 



Ptychopteria elongata, n. sp. 



PLATE I.XXXV, FIGS. 10-13. 



Shell of medium size, sub-rhomboidal, elongate ; body sub-cylindrical, 

 oblique at an angle of 30° with the hinge-line ; length more than one-third 

 greater than the height ; anterior margin oblique, curving into the basal 

 margin, with a slight concavity for the byssal sinus ; posterior margin 

 abruptly rounded. 



Left valve regularly convex below, gibbous above. Right valve somewhat 

 depressed-convex. 



Hinge-line straight, about one-fifth less than the length of the valve. 



Beaks near the anterior fourth of the hinge, directed forward ; left beak 

 prominent, sub-acute, arching over the cardinal line ; beak of right valve 

 depressed, obtuse, scarcely rising above the hinge-line. Umbo gibbous in 

 the left valve ; the greatest convexity of the valve is about one-third the 

 length from the beak. Umljonal angle acute. 



Anterior end short, produced and acute at the extremity, limited by a 

 distinct oblique byssal depressit)u. ^Ying narrow-triangular, joining the bod_v 

 of the shell near the posterior extremity, limited by a furrow which is not 

 conspicuous in the lower part, but in the right valve is more marked; margin 

 ol)liquely truncate. 



Surface marked by fine radii, Avhich are distinctly cancellated hy the con- 

 centric strise, when the specimen is tolerably well-preserved ; also by concen- 

 tric lines of growth which, at somewhat regular intervals, are sharply elevated. 

 The radii are obsolete on tlie anterior of the valve, and the concentric strise 

 are lamellose. 



