GASTEROPODA OF THE LOWER GREEN MABLS. 165 
Formation and locality: Mr. Gabb says the specimen was from the Green 
Marls in Burlington County, New Jersey. The specimen belongs to the col- 
lection Acad. Nat. Sci., Phila. 
BULLID. 
Genus BULLA Linneus. 
BULLA MORTONI. 
Plate xx, Figs. 7-9. 
Bulla Mortons Lyell and Forbes: Quart. Jour. Geol. Soc., London, vol. 1, 1845, p. 
63, Fig A; Gabb, Synopsis, p. 41; Meek, Check List Cret. and Jur. Foss., 
p. 16; Geol. N. J.. Newark, 1868, p. 728. 
Shell rather above a medium size in the larger individuals, two of the 
casts before me measuring almost 14 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 perforate, indi- 
cating a solid axis or spire of considerable dimensions, 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. 
This shell was described by Lyell and Forbes as long ago as 1843, and 
an excellent figure given of a medium-sized individual. It is readily dis- 
tinguished from B. conica, herein first described, by the point of greatest 
diameter being nearly centrally located, while in that one it is at about the 
