458 CRETACEOUS PALEONTOLOGY. 



many instances both valves conform in producing' a deep sinu- 

 osity on the anterior side below the beaks. Surface of the flat 

 valve very strongly lamellose on the posterior half, while show- 

 ing incipient costss on the anterior side below the apex." (Whit- 

 field.) 



Remarks. — All specimens of Exogyra from the New Jersey 

 Cretaceous faunas have usually been placed together in a single 

 species, B. costata, but twO' entirely distinct forms, can be recog- 

 nized, which are characteristic of distinct horizons, and no con- 

 necting varieties between the two forms have been detected in 

 New Jersey. Say does not mention the locality of the type 

 specimen of his species, except that it came from' New Jersey, 

 but it was probably collected at Mullica Hill, since all the 

 other New Jersey Cretaceous species described in his paper, of 

 which the locality is mentioned, are from that place, and fur- 

 thermore, the species has been found to occur abundantly at that 

 locality in the recent collections of the Survey. B. costata is 

 characteristic of the Navesink fauna, and differs from B. pon- 

 derosa oi the Marshalltown fauna, in its strongly costate shell, 

 which, even in the largest individuals, does not develop the 

 strong, concentric, lamellose extensions which are so character- 

 istic of B. pondero'sa. 



Bormation and locality. — Navesink marl, Atlantic Highlands 

 (io8), Middletown (113^, 113^), near Red Bknk (120), near 

 Crawfords Corner (126''), near Holmdel (128^, 127, 194), near 

 Freehold (133), near Walnford (148^), Crosswicks Creek (149, 

 147^ 147^, 147*, 195), near Jacobstown (150), near Mount 

 Laurel (166), Mullica Hill (169^); Red Bank sand. Red Bank 

 (119); Tinton beds. Beers Hill Cut, south of Keyport (129^, 

 1298). 



Geographic distribution. — New Jersey, Delaware, Alabama, 

 Mississippi, Texas, Arkansas.. 



Exogyra ponderosa Roemer. 



Plate XI. VII., Fig. 2. 



1849. Bxogyra ponderosa Roem., Texas, p. 395. 

 1852. Bxogyra ponderosa Roem., Kreide von Texas, p. 71, 

 Taf. 9, figs. 2 a-b. 



