154 MOLLUSCA SUB-KINGDOM VI 
Nerita, Linn. (Fig. 854). Thick, ovoid, or semi-globose, imperforate. Surface 
smooth or with spiral ribs. Inner lip callous, flattened, with a straight, often den- 
ticulate border. Operculum sub-spiral. Trias (?) to Recent. 
Oncochilus, Petho (Fig. 855). Smooth; inner lip arched, callous, bearing two or 
three teeth on the margin or smooth ; outer lip sharp. Trias and Jura. 
Lissochilus, Petho (Fig. 856); Neritodomus, Morr. and Lyc.; Neritoma, Morris, 
Jura. Otostoma, Arch. ; Dejanira, Stol. Cretaceous. 
Velates, Montf. (Fig. 857). Depressed conical, only the curved apex of the spire 

Fic. 854. 
A, Nerita Laffoni, Merian. Citharella Limestone ; Epfen- 
hofen, near Schaffhausen, Switzerland. 6B, N. granulosa, 

Desh. Eocene (Sables Moyens); Auvers, near Paris. Oncochilus chromaticus, Zittel. Upper 
C, Operculum of a recent Nerita. Tithonian ; Stramberg, Moravia. 
visible. Last whorl very large. Inner lip convex or straight, with denticulate margin. 
Abundant in the European Eocene ; sometimes attaining a size of 10 or 12 em. 
Neritina, Lam. (Fig. 858). Small, semi-globose, lustrous, smooth or spiny, mostly 
brilliantly coloured. Inner lip flattened, with sharp or finely toothed margin ; outer 

Fia. 856, 
Lissochilus sigaretinus, Buy. 
Coral-Rag; Hoheneggelsen, 
Hannover. 

Fic. 858. 
Neritina  Gratelowpana, Fer. 
Miocene ; Hiufelburg, near Giinz- 
burg. 

Fic. 859. Fig, 857. 
Pileolus plicatus, Sowb. Bathon- Velates Schmidelianus, Chem. Eocene (Lower 
ian; Langrune, Calvados. 3/. Meeressand) ; Cuise-la-Mothe. 
lip sharp. Inhabits brackish or fresh water. Abundant in Tertiary and Recent. The 
supposed Mesozoic forms belong principally to Nerita. 
Pileolus, Sowb. (Fig. 859). Small, cup-shaped to depressed conical, ovoid or round. 
Apex slightly curved backwards ; only the last whorl visible. Aperture semi-circular ; 
inner lip broad, callous. Jura to Eocene, 
