LAMELLIBRA NCHIA TA . L33 



Anterior end short, small, acute, limited by a shallow byssal depression. 

 Wing large, triangular, extending to near the posterior extremity of the body ; 

 margin slightly oblique, scarcely concave; extremity apparently noi produced. 



Surface marked by fine radii which are more or less interrupted by the 

 varices of the concentric stria 1 , and are frequently undulating. The concentric 

 stria? are often fasciculate, and in their usual condition give an undulated 

 appearance to the cast, but where well-preserved they are angular and some- 

 what lamellose. 



Interior unknown, except a narrow groove along the ligamental area of 

 the hinge. 



A left valve of usual dimensions has a length of 30 mm., height 19 mm., 

 hinge-line 23 mm. A similar right valve has a length of 31 mm., height 18 

 mm., and hinge-line 22 mm. 



This species differs from P. Proto in its less angular posterior slope and 

 posterior end ; the margin of the wing is less oblique to the hinge and the 

 extremity is not produced. 



The specimens occurring in a conglomerate or coarse sandstone have Keen 

 subjected to different degrees of pressure and maceration, and consequently 

 present a great variety of aspect in the surface ornamentation. The furrow 

 and fold limiting the wing are always less conspicuous in the left valve; and 

 in some cases when the shell has suffered pressure these characters are \ en- 

 obscure. 



Formation and locality. Abundant in a conglomerate of the Chemung group 

 at Panama, Chautauqua county, N. Y. 



Ptvchopteria Eucrate. 



PLATE XXIII, FIG. -'4; PLATE I.XXW. HGS. ■-•:. 28. 

 Ptychopteria Kucrate, Hall. Pal. N. Y., vol. v. pt. 1. Plates ami Explanations : PI. •_■:'.. fig. 24. Jan., 1883. 



Shell above the medium size, rhomboidal; body very narrow, elongate-ovate. 

 oblique at an angle of about 30° with the hinge-line ; length nearly twice 

 the height; ante-byssal margin oblique, curving into the sinus; the ventral 



