NERITOPSIS. 339 



1851. Pileoltjs ljevis, Sow. Morris and Lycett, Great Ool. Moll., pt. i, p. 60, 



pi. ix, figs. 37, 37 a, 37 b. 



1852. — — — d'Orbigny, Terr. Jur., ii, p. 240, pi. ccciv, figs. 1 — 4. 

 1854. — — G. Sow. Morris, Cat., p. 268. 



? Syn. Patella mammillaris, Milnst. Goldf., Petref. Germ., pi. clxvii, fig. 10. 



Description .- 



Height ..... 1*35 mm. 

 Basal length . . . .7 mm. 



Shell elliptical, extremely depressed, apex subcentral ; surface smooth, or only 

 marked with indistinct furrows ; the cushion is central ; there are no indications 

 of any crenulation on the inner lip. 



Relations and Distribution. — It is not possible fully to verify Sowerby's 

 diagnosis either for this or the preceding species. Morris and Lycett recognise 

 the form in the Great Oolite of Minchinhampton. D'Orbigny 's figure may 

 represent this species, though it is too orbicular. 



A single specimen from the "Base bed," Lincoln. Quoted from the Inferior 

 Oolite of the Cotteswolds by Morris and by Witchell. 



Family— NERITOPSIMJ. 



"Shell neritiform or naticiform, imperforate, solid ; aperture entire, semilunar 

 or oval; lip arched; columella slightly excavated, internal septa, not entirely 

 absorbed. Operculum calcareous, thick, non-spiral." — Fischer. 



This family is limited to the genera Neritopsis and Naticopsis, whose opercula 

 have in former days puzzled alike the Mesozoic and Palaeozoic palaeontologist. 



Genus — Neritopsis, Grateloup, 1832. 



Shell imperforate, sub globular, neritiform, solid, fetv-whorled ; spire short ; 

 surface ornamented ivith spiral bands and axial ribs or strice. Aperture semicircular, 

 entire, columellar side not denticulated, excavated toivards the middle ; lip simple, 

 thick. Operculum scutiform, not spiral ; upper surf ace provided with a wide truncated 

 appendix which fits into the columellar notch. — Modified after Fischer. 



It must be admitted that none of the specimens figured in illustration of this 

 Monograph, though as good as any which can be procured on this side of the 

 Channel, exhibit the columellar notch so characteristic of Neritopsis. Moreover 



