152 PALEONTOLOGY OF NEW YORK. 



Ptychoptekia kxpansa. 



PLATE XXIII, FIGS. 10, II. 



PlyrliiiplerUi tj-iHiusH, Halt.. Pal. N. V.. vol. v. pt. 1. Plates and Kxjilanatioiis : PI. 23, tigs. 10, 11. 



Jan., 1883. 



Shell of medium size, .sub-rhomlioiil.il : body ovate, oblique at an angle of 

 aliout (10° with tlii' hintic-linc : Ininth one-fifth greater than the height; 

 ante-byssal luargin oblique, gently eurving intu the shallow sinus; basal 

 margin broadly rounded to the l)ase of the wing. 



Left valve convex lu'low, gilibous above. Right valve uidsiiowu. 



Hiuge-line straight, central, length greater than the length of the valve. 



Beak at al»)uT the anterior Hftli of the hinge, inclined acutely forward, 

 moderately prominent, rmlional angle acute. 



Anterior I'lid sinall, surface convex to the nearly vertical byssal depression 

 whicli exti'iids lialf way to the base of the shell; extremity compressed and 

 acute. Wing very large, triangular, extended, joining the body at the 

 posterior extremity ; the furrow obscurely marked ; margin gently concave, 

 extending backward ; extremity produced. 



Surface marked by regular strong radii and by concentric lines of growth. 

 The concentric stria; are sometimes crowded into irregular fascicles, giving 

 an umhilated ain)earance to the surface; the radii are strong on thi' umbonal 

 slope, less conspicuous on the wing, and on the antero-basal portion tlu-y are 

 interruptetl, and obrupie to those on tlie umbo. 



Interior unknown. 



The si)ecimen described has a length of 27 iniu., lu'ight 22 mm., ami hinge- 

 line oO mm. 



This species is distinguished by its erect form, large and extended wing, and 

 peculiar character of surface markings. 'I'lie I'urrow of the wing is indicated 

 only by a wider depression between the radii, and a strongei- ray marks the 

 fold. 



Formation and localitij. Tn a coarse sandstone of tlie Chemung gionp near 

 Smethport, Pa. 



