630 CRETACEOUS PALEONTOLOGY. 



Description. The dimensions of the type specimen are : 

 length, 26 mm. ; height, 15.5 mm. Shell subquadrangular in out- 

 line, a little broader behind than in front; beaks broad, rather 

 strongly elevated above the hinge-line, nearly central in position 

 and directed anteriorly. Hinge-line nearly straight, the anterior 

 and posterior portions sloping very gently on each side of the 

 beak; antero-cardinal margin concave; anterior margin rounding 

 from the cardinal into the basal margin; basal margin nearly 

 straight or slightly convex in the middle, curving upward a little 

 more abruptly in front than behind; postero-basal extremity 

 rounded ; posterior margin nearly vertically truncate ; post-cardi- 

 nal extremity obtusely subangular ; post-cardinal margin straight. 

 Valves moderately convex, with an obscure, rounded, umbonal 

 ridge along both the anterior and posterior umbonal slopes ; the 

 cardinal margins inflected both in front and behind the beaks. 

 Surface of both valves in the casts marked by rather fine, more 

 or less irregular, concentric lines of growth. 



Remarks. This shell, in its general outline, somewhat 

 resembles Pcriplomya elliptica, but with the extremities of the 

 shell reversed, the anterior extremity of that species being the 

 broader and the beak being directed backward. In Solynna lin- 

 eolata, however, the posterior margin is truncate while the ante- 

 rior margin of P. elliptica is rounded, and the anterior extremity 

 is much broader than the posterior extremity of that shell. The 

 two more or less obscure umbonal ridges are also a distinguish- 

 ing mark of this species, but these ridges have been made too 

 conspicuous in Whitfield's illustration of the species. Upon one 

 of the internal casts of this species which has come under obser- 

 vation, there seems to be an impression of a very deep pallial 

 sinus extending forward to the center of the shell. 



Formation and locality. Cliffwood clay, near Matawan 

 (186); Merchantville clay-marl, near Miatawan (101), near 

 Jamesburg (139), Linola (163); Woodbury clay, Lorillard 

 (102), near Matawan (103), near Haddonfield (183); Weno- 

 nah sand, near Marlboro (130); Red Bank sand, Red Bank 

 (116). 



Geographic distribution. New Jersey, Georgia. 



