1-^ PALEONTOLOGY OF NEW YORK. 



PtYCHOPTERLA BXPANSA. 

 PLATE XXIII. PIGS. 1», II. 



Plychopteria expansa, Ball. Pal. \. V.. vol. v, pt. 1. Plates and Explanations: PI. 23, figs. 10, 11. 



Jan., 1883. 



Shell of medium size, sub-rhomboidal ; body ovate, oblique at an angle of 

 aboul 60° with the hinge-line; length one-fifth greater than the height; 

 ante-byssal margin oblique, gently curving into the shallow sinus; basal 

 margin broadly rounded to the base of the wing. 



Left valve convex below, gibbous above. Right valve unknown. 



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



Beak at about the anterior fifth of the hinge, inclined acutely forward, 

 moderately prominent. Umbonal angle acute. 



Anterior end small, surface convex to the nearly vertical bvssal depression 

 which extends halt' 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 undulated appearance to the surface; the radii are strong on the umbonal 

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

 interrupted, and oblique to those on the umbo. 



Interior unknown. 



The specimen described has a length of 21 nun., height '22 mm., and binge- 

 line 30 nun. 



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

 peculiar character of surface markings. The furrow of the wing is indicated 

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

 fold. 



Formation and locality. In a coarse sandstone of the Chemung group near 

 Smethport, Pa. 



