434 - CRETACEOUS PALEONTOLOGY. 



right just to its margin. Right valve with a deep notch-like slit 

 on the anterior side just below the hinge, with a narrow, deep 

 groove running from it to the apex of the valve on the exterior 

 surface. Left valve provided with an internal fold, quite indis- 

 tinct except under a glass, on the anterior side of the beak, which 

 corresponds to the byssal notch of the right valve. Anterior 

 margin of the valve somewhat regularly rounded ; basal margin 

 broadly rounded, and the posterior obliquely truncate, passing 

 backward slightly from the hinge extremity to the postero-basal 

 line. Surface of the valves smooth or very finely lamellose, and 

 marked with concentric undulse. When not at all worn or mace- 

 rated the surface of the left valve shows indistinct thread-like, 

 interrupted, radiating lines which remind one very strongly of 

 those seen on species of Placunomya." (Whitfield). 



The dimensions of the right valve illustrated by Whitfield are : 

 length, 14.5 mm.; height, 12 mm. 



Remarks. This species has been met with but rarely in the 

 recent collections of the Survey. 



Formation and locality. Navesink marl, near Holmdel 

 (i28 3 ), near Freehold (Whitfield). 



Geographic distribution. New Jersey. 



Super-family OSTRACEA. 



Family OSTBEIDAE. 



Genus OSTREA Linneus. 



Ostrea cretacea Morton. 



Plate XLIL, Fig. 11. 



1834. Ostrea cretacea Mort, Synop. Org. Rem. Cret. Gr. U. S., 

 p. 52, pi. 19, fig. 3. 



1860. Ostrea cretacea Owen, 2d Rep. Geol. Recon. Ark., pi. 7, 



fig- 7- 



1861. Ostrea cretacea Gabb, Proc. Acad. Nat. Sci. Phil., 1861, 



p. 328. 

 1861. Ostrea cretacea Gabb, Synop. Moll. Cret. Form., p. 208 



