LAMELLIBRANCHIATA. | | 



• i 



Hinge-line straight, length about one-seventh less than the greatesl length 



of the valve. 



Beaks at about the anterior fourth, prominent ami incurved over the hinge- 

 line in the left valve; depressed in the right valve and not rising above the 

 cardinal line. Umbonal angle nearly rectangular. 



Anterior end large, limited by a broad, slightly oblique, undefined byssal 

 depression; extremity acute and nasute. Wing elongate triangular, joining 

 the body at the posterior end ; the dividing furrow distinct in the left valve, 

 inore conspicuous in the right ; the fold is not defined in the left valve, and is 

 strongly marked in the right; margin nearly vertically truncate; extremity 

 not perceptibly produced. 



Test thin, marked by fine radii, which are conspicuous upon the body and 

 wing, and obsolete on the anterior end and byssal depression. The surface 

 is also marked by tine concentric stria3, which are crowded into fascicles, 

 giving an apparent undulation to the surface from the umbo to the lower 

 extremity, especially in the right valve. At the post-basal margin the 

 stria? are recurved at a little less than a right angle in the left valve, and 

 more acutely in the right valve, and they are strongly lamellose on the 

 anterior end. 



Interior unknown. 



The specimen described has a length of 56 mm., height •'!<> mm., and 

 hinge-line about 48 mm. 



This species resembles P. lata, anil also some forms of P. Sao, but it is much 

 more elongate, the valves more depressed, the wing narrower and longer. 

 Formation and locality. In the Upper Chemung group at Warren, Pa. 



Ptychopteria lata, n. sp. 



PLATE I.NXXV. FIGS. -r.\ -i>. 



Shell large, rhomboidal; body sub-elliptical, very oblique, making an angle 

 with the hinge of nearly 40°; height equal to about two-thirds of the length : 

 ante-byssal margin oblique, curving into the shallow sinus, from whence the 



in 



