38 NERITELLA. 
Family NERITIDZ. 
Genus NERITELLA, Aumphrey. 
Shell globular, or globose-conical, thin, with 
a horny epidermis, and a large semilunar aper- 
ture, the inner lip of which is straight and 
flattened with a smooth or denticulated mar- 
gin, outer lip-margin rounded, simple, acute. 
Operculum sub-spiral, testaceous, smooth on 
the exterior surface, with two apophyses or 
ridges, of which the upper one is short, and 
the lateral one in the form of an arched rib. 
Animal. Head with a short, broad muzzle, 
slender tapering tentacles, with pedunculated 
eyes at their outer bases; foot oblong, triangu- 
lar, the sides simple. 
Distribution.—Tropical and subtropical. 
Most of the species belonging to this family 
and genus are marine, many of them, however, 
inhabiting brackish water. Of the six species 
described and figured in Mr. Binney’s recent 
publication on the “Land and Fresh-Water 
Shells of North America,” three, viz. : cassicu- 
* Smithsonian Miscellaneous Collections. 8vo. Wash- 
