MOLLUSCA. 813 



1861. Bulla Mortoni Gabb, Synop. Moll. Cret. Form., p. 97 



1864. Build Mortoni Meek, Check List Inv. Foss. N. A., Cret. 



and Jur., p. 16. 



1864. Solidula Mortoni Con., Cook's Geol. N. J., p. 728. 

 1864. Bulla Mortoni Con., Cook's Geol. N. J., p. 728. 

 1892. Bulla Mortoni Whitf., Pal. N. J., vol. 2 (Monog. U. 



S. G. S., vol. 18), p. 165, pi. 20, figs. 7-9. 

 1892. Bulla conica Whitf., Pal. N. J., vol. 2 (Monog. U. S. 



G. S., vol. 18), p. 189, pi. 23, figs. 12-13. 

 1905. Btdla<mortoni]ohns., Proc. Acad. Nat. Sci. Phil. (1905), 



p. 19. 



Description. "Shell rather above a medium size in the larger 

 individuals, two of the casts before me measuring almost i l /4 

 inches in length, with a transverse diameter of three-fourths of 

 an inch. Form, elongate oval, almost equal in size above and 

 below the middle, the upper end perceptibly the smallest, and the 

 point of greatest diameter rather below the middle of the length. 

 Upper end slightly truncate, and in the cast rather strongly per- 

 forate, indicating a solid -axis or spire of considerable dimen- 

 sions, the outer lip of the aperture rising somewhat above the 

 truncation; aperture very elongate, narrow and rounded above, 

 scarcely widening for the upper third of its length, then rather 

 rapidly expanding below, but principally on the inner side, to 

 twice the width at the lower third of that of the upper third of 

 the length; base pointedly rounded and projecting considerably 

 below the opposite part of the body whorl. Columella thickened 

 and showing slight indications of an angularity on its inner edge, 

 not visible except with a glass, looking within the cavity, then 

 only on the larger well preserved specimens. Surface marked 

 throughout with fine, nearly equidistant, spiral, depressed lines 

 and obscure transverse undulations of irregularity of growth." 

 (Whitfield.) 



Remarks. So far as known, this species occurs only in the 

 Navesink marl, and being the only similar shell in the fauna of 

 that formation, it can always be easily recognized. The example 

 which Whitfield used as the type of his species B. conica is pre- 



