GASTEROPODA. 261 
Shell thick, smooth or spirally grooved; epidermis horny; 
outer lip thickened and sometimes denticulated St 
within; columella broad and flat, with its inner 
edge straight and toothed; operculum shelly, 
Fig. 112. 
Distribution, 178 species. Nearly all warm seas. 
West Indies, Red Sea, Zanzibar, Philippines, Fig. 112.* 
Australia, Pacific, West America. (Cuming.) Many of the 
American species dwell in the streams; one species at the 
Philippines sometimes climbs up trees. 
Fossil, 60 species. Lias—. Britain, &c. The paleeozoic nerites 
are referred by D’Orbigny to turbo, natica, &c. N. haliotis isa 
pileopsis. 
Sub-genera. Neritoma, Morris, 1849. N. sinuosa, Sby. 
Portland stone, Swindon. (Mus., Lowe.) Shell ventricose, 
thick; apex eroded; aperture with a notch in the middle of the 
outer lip. Casts of this shell are common, and exhibit the 
condition of the interior characteristic of all the nerites ; 1t was 
probably fresh water. 
Neritopsis, Grateloup. N. radula (Pl. VIII, Fig. 9). Shell 
like nerita ; inner lip with a single notch in the centre, 
Distribution, 1 species. Pacific. 
Fossil, 20 species. Trias? Britain, France, &c. 
Velates, Montf. WN. perversa, Gm. (Pl. [X., Fig. 36). Inner 
lip very thick and callous; outer lip prolonged behind, and par- 
tially enyeloping the spire. 
PILEOLUS (Cookson), J. Sowerby. 
Etymology, pileolus, a little cap. 
Pype, P. plicatus (Pl. IX., Figs. 37, 38). 
Shell limpet-like above, with a sub-central apex; concave 
beneath, with a small semi-lunar aperture, and a columellar 
disc, surrounded by a broad, continuous peristome. 
Distribution, marine; only known as fossils of the Bath oolite, 
Ancliffe, and Minchinhampton, 8 species, P. neritoides is a 
nerivind. 
NERITINA, Lam. Fresh-water nerite. 
_ wamples, N. zebra (Pl. IX., Fig. 39), N. crepicularia 
(Pl. [X., Fig. 40). 
Shell rather thick at the aperture, but extensively absorbed 
inside; outer lip acute ; inner straight, denticulated ; operculum 
* Fig. 112. Operculum of VY. peloronta, West Indies, 
