307] G. E. Dorsey 109 



Scissure long, occupant la moitie de la cavite". Cavite" 

 ronde, tres-longue, conique, occupant les deux cinquiemes de la lon- 

 guer, pourvues en dessus d'un sillon creux longitudinal; alveole avec 

 des cloisons separges, dont les traces se montrent encore dans la 

 cavite. Jeune, sa form est plus conique et le"gerement comprime'e." 



Despite the fact that B. americana and B. mucronata are 

 regarded as type fossils, and that the two forms are regarded 

 as closely related, they do not represent exactly the sam^ 

 horizons on both sides of the Atlantic, the American form 

 being somewhat older than its European analogue. 



One of the typical American occurrences is in the Mon- 

 mouth formation of the Upper Cretaceous of New Jersey. 

 J. A. Gardner (4, p. 396) says, 



"It (B. americana) is perhaps the most valuable horizon marker 

 of the Cretaceous, since it has never been reported from either above 

 or below the Monmouth, and is determinable from the merest frag- 

 ment." 



The Monmouth formation, whose type locality is in Mon- 

 mouth County, New Jersey, has been divided by W. B. Clark, 

 in ascending order, into the Mt. Laurel sands, the Navesink 

 marls, and the Redbank sands. The Belemnitella zone in 

 New Jersey occurs at the Navesink marl level and thus is 

 about midway in the Monmouth. To the south, B. americana 

 is found in the Peedee formation of North and South Caro- 

 lina, and farther to the south in the Exogyra costata zone 

 of the Selma Chalk. 



It apparently dies out before the deposition of the upper 

 Monmouth. In Europe, B. mucronata is first found in the 

 late Campanian. It continues throughout the Maestrichtian, 

 that is throughout the Aturian or uppermost Senonian. The 

 overlying Danian from which it is absent is correlated with the 

 New Jersey Rancocas and Manasquan formations. Thus, if, 

 as Clark says (4, p. 74), "The (Monmouth) forms point 

 to the lower Senonian age of the beds," then the presence of 

 B. mucronata in the Maestrichtian is decidedly younger, 

 particularly so since Belemnitella is not present in America 

 even in late Monmouth time. 



