140 EOCENE MOLLUSCA. 
shorter spire and a narrower aperture than J/. colwmbellina, and the columellar plaits 
are more strongly bifid than in that species. The outer lip in the adult shell also is 
flattened in front, and its inner margin presents a sharp edge; whereas in the French 
species the outer lip is rounded and rather involute. I must state that in the young 
shell, the columellar plaits in 17. difido-plicata are thin and simple, and that the bifid 
character is assumed only at maturity. 
The other species from the calcaire grossier (M. contabulata), to which I have 
before referred, appears to be a longer and narrower shell than the present one; the 
whorls are distinct, notwithstanding the enamel, and present an obscure channel 
running round the suture; the mouth is more effuse in front, the outer lip not so much 
thickened, the posterior sinus obscure, and the columellar plaits more oblique. 
The present species is found in profusion in the Highcliff sands ; and sparingly in 
the Barton Beds. Specimens are also found, rather plentifully, in the corresponding 
stratum (No. 29, of Mr. Prestwich), in Alum Bay, larger and more regular in form and 
with a somewhat longer spire than the type, but agreeing with it in all essential 
characters (figs. 2 e—g), and I consider the last, therefore, to be merely a local variety. 
It also occurs in the stratum No. 4, Prestwich, in Alum Bay, and at Bracklesham Bay. 
The specific name is taken from the bifid condition of the columellar plaits, a character 
found, however, in several other species belonging to this group, although not so 
strongly marked as in the present one; it was proposed by Mr. Charlesworth, in a 
lithographic print of the species forming part of a series of figures of shells from 
Highcliff and Barton, beautifully executed, under the direction of that gentleman, for 
distribution among the members of the “ Natural History Society.” 
Size.—Type, Axis, somewhat less than 2-10ths of an inch; diameter, 1-10th of an 
inch. 
No. 82. MARGINELLA GRACILIS. Ff. #. Edwards. Tab. XVIII, figs. 4 a—e. 
M. testé minimd, tenut, subfusiformi, ad basin vie emarginata ; spird elevatd, conicd, apice 
obtuso: anfractibus quinque, convexis: apertura elongato-ovali, in tongitudine spiram superantz, 
postice obscure canaliculatd ; labro incrassato, eatus marginato ; columella quadriplicata, 
plies tribus posticis obliquis, bifidis. 
Shell very small, slender, tapering nearly equally towards each extremity; spire 
elevated, conical, with an obtuse apex; whorls five, convex, the last whorl scarcely 
notched at the base: aperture of a lengthened oval shape, moderately wide, and rather 
longer than the spire; outer lip thickened within, and presenting a narrow, slightly 
raised border along the outer margin, and a small obscure channel at the suture ; 
columella with four folds, of which the posterior three are bifid, and rather oblique. 
This may be merely a variety or an immature state of JZ. difido-plicata, and, as I 
have only two specimens before me, I have separated it with much hesitation. The 
