330 Thirty-fifth Report on the State Museum. 



Ptyohopteria expaksa. 



Ptychopteria expansa, Hall. Pal. N./ST. , 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 about 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 un- 

 known. 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 byssal 

 depression which extends half way to the base of the shell • 

 extremity compressed and acute. Wing very large, triangular, ex- 

 tended, joining the body at the posterior extremity; the furrow ob- 

 scurely marked ; margin gently concave, extending backward ; 

 extremity produced. 



Surface marked by regular strong radii and by concentric lines of 

 growth. The concentic striae 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. 



The specimen described has a length of 27 mm., height 22 mm., 

 and hinge-line 30 mm. 



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. 



