in-2 PALjEONTOLOnr OF NEW YORK. 



lines, whicli aiv irrciiularh' n'<)\v(l('(| into siil)-iinbricatiug lamella?. On tin- 

 anterior end of the valve the railii are cancellated by the concentric stritv. 



Interior charaeters unknown, except a narrow groove along the ligamental 

 area. 



A left valve has a length ol' 41 mm., height "ii mm., hinge-line 32 mm. 

 A similar right valve has a length of 40 iiini., height 24 mm., liiiige-line 

 34 mm. 



This species varies in different conditions of preservation. The obtusely 

 sub-angular appearance of the posterior slope is often exaggerated by lateral 

 pressure or subdued by vertical pressure. The same is true of the folds of the 

 wing. Tn some ecmditions the radiations are continuous, in others they are 

 cancellated. In weathered specimens the stride are sometimes nearly obsolete, 

 and the concentric lamella? more prominent. 



Formation and locality. In the Chemung group, in a sandstone above the 

 conglomerate at Hock City, near Salamanca, N. Y. 



Ptychopteria Sao. 



PLATE XXin, KIGS. 10, Si; AM) PLATE I.XXXV, FICS. 14-1?. 



riiirhi.plinii .SVr-i. Uw.i.. I'al. N. v., vol. V, pt. I. I'hitus and K.\i>laiiatioiis : PI. 23, tigs. IG, 23. 



Jan.. 1883. 



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

 angle of about 4")' with the hinge-line; length one-third greater than the 

 height ; ante-byssal margin obrn|uely sub-truncate, gently eur\ing into the 

 sinus; base broadly rounded; posterior margin extendt'd, abru[>tly recurved 

 to the wing. 



\'alves convex; left valve larger and UKU'e convex than the right. 



liinge-line straight, longer than the heiglit of the valve. 



IJeak in front of the anterior third of the cardinal line obtuse, jiroiuineut in 

 the left valve and arching over tlie hinge; less prominent in the right valve, 

 and rising just ahove the hinge. Tmbo gibbous in the leit valve, less gibbous 

 in the rijiht, subtendini: an acute anule. 



