378 NERITIDiE. 



iial portions of the whorls ; aperture semi-ovate, not 

 pearly within. 



In this tribe of Scutibranchiate Mollusks the sides 

 of the foot are without membranous fringes and tenta- 

 cular filaments, the animal is not voluminous, and the 

 foot is small and never envelopes the shell ; in their 

 dental system they resemble the Trochid(e^ as also in 

 their muzzle-shaped heads and pedunculated eyes. 

 They are littoral animals, inhabiting the stones and 

 rocks along the shore, feeding on the algae that abound 

 in that situation. They appear to be more active during 

 the night, resembling, in this respect, the Palellidre, 

 which are said to enjoy considerable locomotive powers 

 at that time. 



Genus NERITA, Linnaeus. 



Animal with the mantle-margin festooned. 



Operculum horny, solid, with a shelly coat on each 

 side, the outer surface usually granular, when smooth, 

 with circular grooves, the edge channelled. 



Shell generally solid, thick, semi-globose, smooth or 

 spirally grooved, often covered with a horny epidermis; 

 aperture semilunar; inner lip broad, flattened, the front 

 edge straight, with a few very prominent teeth ; outer 

 lip thickened, dentate, crenulate or grooved internally. 



Sy7i. Odontostoma, Klein, not D'Orh. Neritarius, 

 Dum. 



Ex. N. polita, Linnaiis, pi. 42, fig. 1. Operculum, 

 N. polita, fig. 1, «, 1, h. Shell, N. polita, fig. 1, c. 



The Nerites proper may be known at once from the 

 sub-genera by the septiform plane of the inner lip 

 being smooth or nearly smooth. All the species are 



