Lamellibeanchiata. 313 



This species resembles P. sinuosa, but the anterior end is wider ; 

 the wing is smaller and not produced at the extremity, and the radii 

 are coarser. These two species are distinguished from the forms 

 which follow by the large anterior end which is separated from the 

 body by a broad byssal depression. 



Formation and localities. In a coarse sandstone, from a bowlder con- 

 taining the same associated fossils as a sandstone at Portville, Catta- 

 raugus county, N. Y. ; probably of the Upper Chemung group, 

 Smethport, McKean county, Pa. 



Pttchopteeia sistuosa. 



Ptychopteria sinuosa, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : 

 PI. 23, fig. 13. Jan., 1883. 



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

 angle of about 40° with the hinge-line ; length more than one-third 

 greater than the height; ante-byssal margin nearly vertical, curving 

 into the broad sinus; base broadly rounded; posterior margin 

 recurving into the wing. Left valve convex below, gibbous in the 

 middle and above. Righi valve unknown. Hinge-line straight, 

 length four-fifths the length of the shell. Beak at about the 

 anterior third of the hinge, acute, directed forward. Umbonal 

 region strongly gibbous, limited by the abrupt depression of the 

 body on the posterior side, and by the byssal depression on the 

 anterior side. Umbonal angle about 30°. Anterior end large, 

 narrow, rounded, defined by a broad, shallow, nearly vertical byssal 

 depression ; extremity angular. Wing narrow-triangular, extending 

 nearly to the posterior extremity of the body ; margin nearly vertical, 

 slightly concave ; extremity somewhat produced, angular. 



Surface marked by fine undulating radii, which are less conspicu- 

 ous on the wing, and by fine concentric lines of growth, which are 

 crowded into sub-imbricating lamellae. On the anterior side of the 

 body the rays are cancellated by the elevated concentric striae. The 

 ligamental area shows a sharp linear groove extending three-fourths 

 of its length posterior to the beak, and a narrow cardinal tooth 

 anterior to the beak and parallel to the hinge. 



A large specimen of the left valve has a length of 31 mm., height 

 19 mm., and hinge-line 25 mm. A smaller one has a length of 24 

 mm., height 13 mm., hinge-line 20 mm. 



This species has a narrower anterior end than the preceding, a larger 

 and more extended wing, finer and undulating striae. 

 [Sen. Doc. No. 38.] 40 



