LAMELLIBllANCHIATA FROM THE EOCENE MARLS. 237 



tooth on each side and a single strong, hook-4ike tooth in tlie center beneath 

 the beak, with a similarly-shaped cavity in front of it, presenting a true 

 Cardiiim hinge. The plate for the attachment of the ligament, however, 

 cannot be made out. The nmscular scar on the anterior side has been 

 very faint, seldom being seen on the cast, but the posterior scar has been 

 deeper, and sometimes leaves a deep groove bordering it on the cast, repre- 

 senting a ridge on the shell. 



The species presents the external form of a Protocardium, but differs 

 somewhat in the surface markings, as it is striated throughout. Mr. Conrad 

 described the "ventral margin minutely crenulated," but on some of the casts 

 the striae on the body of the shell can be traced to near the middle of the 

 valve, showing that they are the remains of external striae, and not merely 

 the crenulations of the internal margins of the shell. I have not seen the 

 external markings in imprints of the shell, as there appears to have been 

 none of these preserved in collections. The representation of the hinge of 

 a left valve is given on the plate as nearly as it could be obtained from a 

 gutta-percha impression taken in the best cast which I have observed. 



Formation and locality. — In the Eocene layer of the Upper Marls at 

 Farmingdale, Squaukum, and Shark River, New Jersey. Apparently not a 

 rare species. 



VENERIDiE. 



Geuus GARTATIS Roemer. 



Caryatis ovalis, u. sp. 



Plate XXX, Figs. 15 and 16. 



Caryatis Dclaicarensis Conrad. Am. Jour. Coucb., Vol. V, p. 41, PI. I, Fig. 6. 

 Not Dlone Delawarensis Gabb. J. A. N. Sci., new scr., Vol. IV, p. 312, PI. XL VIII, 

 Fig. 18. 



Sliell transversel}' short-oval, very oblique, Avith moderately-sized 

 incurved beaks situated near the anterior end, and not projecting above 

 the cardinal umbonal surface posterior to them. Hinge-line only moder- 

 ately arcuate, and about parallel to the basal line, which is also only mod- 

 erately curved. Anterior and posterior ends broadly rounded, the former 

 somewhat more sharply so than the latter, owing to the excavation in front 



