202 NICANIA. 



3. Neritina. Shell thin ; columellar lip septiform, edge 



denticulated ; generally a thick, dark coloured epidermis. 

 Fig. 324 to 326. 



4. Natica. Having an umbilicus behind the columellar lip, 



with a spiral callosity. Fig. 327, 328. 



5. Neritopsis. Edge of the columellar lip with a deep notch. 



Fig. 331. 



6. Pileolus. Patelliform ; apex central 5 columellar lip sep- 



tiform, leaving the aperture small. Fig. 332. 

 7. Janthina. Columellar lip linear; aperture angulated. 

 Fig. 333. 



NERITINA. Lam. Fam. Neritacea, Lam.— Bescr. Thin, semi- 

 globose, obliquely oval, smooth, flattish in front ; spire short, 

 sometimes depressed, consisting of few rapidly increasing whorls; 

 aperture semicircular; outer lip thin, sharp ; columellar lip broad, 

 flat, its inner edge straight, denticulated ; operculum testaceous, 

 semicircular, sub-spiral, with an articulating process on the 

 inner edge. — Obs. This genus of fresh-water shells differs from 

 Nerita in the minuteness of the denticulation of the columella, as 

 well as in the characters mentioned in our observations upon the 

 latter genus. N. spinosa, (Clithon, Montf.) fig. 325. N. virginea, 

 fig. 324. N. perversa, Lam. (Velates, Montf.) fig. 326. All the 

 species known up to the present time, with the exception of 

 three, are represented in the author's Conchological Illustrations, 

 parts 86, 87, 90, 91, 94 to 100. The catalogue accompanying 

 these representations enumerates 59 species. 



NERITOPSIS. Gray. Fam. Neritacea, Lam.— Bescr. Sub-globose, 

 thick, cancellated ; spire short, composed of few rapidly increasing 

 whorls; aperture transverse, sub-orbicular; outer lip thickened 

 within ; columellar lip thick, rather flat, with a large rounded 

 notch in the centre of its inner edge. — Obs. This genus most 

 nearly resembles Nerita, from which it differs in the peculiar 

 notch of the columella. N. granosa, fig. 331. 



NICANIA. Leach. Astarte, Sowerby. The same as Crassina of 

 Lamarck. 



