840 CRETACEOUS PALEONTOLOGY. 



1892. BelemniteUa Americanm Whitf., Pal. N. J., vol. 2 

 (Monog-. U. S. G. S., vol. 18), p. 280, pi. 47, figs, 

 i-ii. 



1905. BelemniteUa americana Johns., Proc. Acad. Nat. Sci. 

 Phil., 1905, p. 28. 



Description. — Guard elongate, tapering, sometimes attaining a 

 rather large size, the length of a large individual being 135 mm., 

 with a maximum thickness of 20 mm. Cross-section subtri- 

 angular in the larger portion, the ventral side flattened; toward 

 the smaller extremity the cross-section becomes more nearly 

 circular or elliptical, the flattening being in a dorso-ventral 

 direction. The alveolar cavity excavating the guard for about 

 one-third, or somewhat more than one-third, its length, the edge 

 of the guard at the aperture of the alveolus becoming very 

 thin and rarely or never being perfectly preserved; the ventral 

 slit extending nearly to the bottom of the alveolar cavity, not 

 produced beyond that point as a ventral groove. The small end 

 of the guard, when perfectly preserved, is produced in a small 

 mucronate extremity. When not worn the surface is rough- 

 ened, most conspicuously upon the broad ventral and the nar- 

 row dorsal sides towards the larger extremity, there being a 

 comparatively smooth, rather narrow, longitudinal band upon 

 each of the sloping dorso-lateral sides. The phragmocone has 

 not been observed, although casts of the alveolar cavity are com- 

 mon, and occasionally one of them retains the impressions of 

 the septal lines. 



Remarks. — This species is, perhaps, the most characteristic 

 member of the Navesink fauna, and has not been observed in any 

 other horizon in New Jersey. It occurs in practically every 

 locality of this formation which is at all fossiliferous, and some- 

 times occurs in so great abundance that hundreds of individuals 

 can be collected in a small area. Most of the specimens, how- 

 ever, have been more or less worn before they have been buried 

 in the sediments, sO' that it is rare tO' find any individual perfectly 

 preserved, most of the very best examples having the thin edge 

 of the alveolar cavity and the mucronate extremity of the shell 



