140 EOCENE MOLLUSCA. 



shorter spire and a narrower aperture than M. columbellina, 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 M. bifido-plicata are thin and simple, and that the bifid 

 character is assumed only at maturity. 



The other species from the calcaire grassier {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, l-10thof an 

 inch. 



No. 82. Marginella gracilis. F. E. Edwards. Tab. XVIII, figs. 4 a—c. 



M. testa minima, tenui,subfusiformi, ad basin vice emarginatd; spird elevatd, conicd, apice 

 obtuso: anfractibus quinque, convexis: aperturd elongato-ovali, in longitudine spiram super anti, 

 postice obscure canaliculatd ; labro incrassato, extus marginato ; columella quadriplicatd, 

 plicis 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 M. bifido-plicata, and, as I 

 have only two specimens before me, I have separated it with much hesitation. The 



