4 NERITID.E. 



in either of the iconographies. I have, in the main, followed his 

 arrangement of the species, although a different disposition of some 

 of the groups has appeared to me more desirable, and has accord- 

 ingly been attempted. In the Xeritinse Von Martens has made the 

 opercular processes the basis of his classification, whilst I have con- 

 sidered characters of the shell as of more importance ; the result is 

 a different succession of groups, whilst their contents remain es- 

 sentially alike. 



Synopsis of Genera. 

 Genus NERITA, Adanson. 1757. 



Shell thick, smooth or spirally ridged and grooved, porcellanous, 

 under a corneous adhering epidermis sometimes wanting; outer 

 lip thick, usually denticulated within, columellar lip flattened, its 

 margin dentate, straight. Operculum calcareous, the outer face 

 granulated or with a decurrent groove, paucispiral, with excentric 

 nucleus, inner face callous, the apical and claviform apophyses well- 

 marked, marginal apophysis more or less developed, corresponding 

 with the groove of the outer face. 



Animal usually with festooned mantle margin. Living on rocks 

 and stones, generally inactive by day, but said to be active at night, 

 roaming about and feeding on algse, etc. Gregarious, and littoral, 

 and nearly exclusively marine. 



About 200 living species have heretofore been recognized, in- 

 habiting tropical and semitropical shores throughout the world. 

 Sixty fossil species have been enumerated, but the earlier forms are 

 somewhat doubtful, and may more probably be referred to Nerito- 

 domus. 

 Section NERITA, Lamarck. 1799 (sensu stricto). 



Columellar lip granular or tuberculated. N. ALBICILLA, Linn. 



Theliostyla, Morch. 1852, and Ncrfere, Gray. 1858, are synonyms. 

 Section PELORONTA, Oken. 1815. 



Columellar lip nearly smooth, its margin strongly dentate, outer 

 lip dentate within. N. PELORONTA, Linn. 



Tenare, Gray. 1858, is a synonym. 

 Section PILA, Klein. 1753. 



Columellar lip rugosely grooved and ridged, its edge dentate, 

 outer lip plicate within, with a large tooth at either extremity of the 

 series. N. PLICATA, Linn. 



Eitena, Gray. 1858, is a synonym. 



