Lamavck's Genera of Shells. 247 



2. Neritina *. 



Shell thin, semi-globular or oval, flattened on the lower 

 part; no umbilicus. Aperture semi-circular ; left lip flattened, 

 acute ; no teeth, nor crenations on the internal face of the right 

 margin. Operculum furnished with a projecting apophysis, or 

 lateral tooth, on one side. 



Fresh-water shells, generally thin, and smooth externally. 



Type. Neritina pulligera t- (Nerita pulligera. Linn.) 



Shell ovate, delicately striated, blackish brown, dotted with 

 small round young shells, which adhere to it; lip dilated, thin, 

 white internally; margin acute; lower border yellowish; lip 

 crenate. 



India. PI. VIII. Fig. 151. 21 species. 



3. Nerita |. 



Shell solid, semi-globular, flattened on the lower part ; no 

 umbilicus. Aperture entire, semi-circular ; left lip flattened, 

 septiform, acute, often crenate; internal face of the right lip 

 crenate. Operculum furnished with an apophysis. 



AH sea-shells, solid, rather thick, and agreeably varied in 

 colour. The spire is but little elevated above the last whorl. 

 The operculum is crescent-shaped, horny, or calcareous, and 

 exactly closes the aperture. When the animal comes out of 

 the shell, the operculum falls back on the flat part of the colu- 

 mella, like a shutter. The nerita differs from neritina by the 

 internal face of the right margin being crenate, and from natica 

 by having no umbilicus. 



Type. Nerita exuvia §. (Idem, Linn.) 

 Shell thick, white, spotted with black; ribs transverse, those 

 on the back acute, rough-squamose, decussated by longitudinal 

 striae ; interior of the lip crenate ; upper part of the margin 

 vcrrucose, and toothed, 



Indian Ocean. PI. VIII. Fig. 152. 17 species. 



4, Natica, 



Shell sub-globular, umbilicated ; aperture entire, semi- 



* Dim. o[ Nerila. -t Bearing; its young. 



Fidiii Kifjii;, the (irceli name for a kind of sen shell, — from, vtu, to swim, 

 because it swiins on the sea. § E.Tuvia; spoils. 



