6 NERITID.E. 



and a claviform apophysis, both arising from the summit, and some- 

 times a medio-marginal apophysis in addition, arising from the 

 colnmellar or inner margin (PI. 1, figs. 9, 10). 



No important differences in the soft parts have been detected be- 

 tween Nerita and Xeritina. Dentition, PL 1, fig. 3. 



About 200 generally recognized species have been described. 

 They are mostly fluviatile, but a few inhabit marine or brackish 

 water, and a very few are of terrestrial habitat. They are mostly 

 tropical and subtropical in distribution. Fossil, they occur from 

 the liassic downwards, the pattern of coloring being well preserved; 

 the genus becomes numerous in species in the miocene and pliocene. 



The Neritinse are small, smooth, globular shells, ornamented with 

 a great variety of black or purple lines, bands or spots, covered by 

 a smooth, polished, horny epidermis. Some species are amphibious, 

 clinging to the roots of Nipah palms and other trees on the mar- 

 gins of rivers, while a few inhabit the foliage of tall trees that over- 

 hang the water. 



Neritella (Humphrey. 1797), Gray. 1847, Lamprostoma, Swains. 

 1840, and Neritcea, Roth, are synonyms. 



Section NERITINA (sensu stricto), Swainson. 1840. 



Lip sharp, columellar lip rather convex, with crenellated margin, 

 parietal ridge well marked, dentiform, form ovoid with rather high 

 spire, usually strigate. Operculum reddish or blackish, both pro- 

 ss well developed, separate. Fluviatile. N. ZIGZAG, Lam. 



Section PUPERITA, Gray. 1857. 



Shell white, with black zigzag strigations, yellowish within. 

 Similar to the above, but marine. 1ST. PUPA, Linn. 



Section NERITODRYAS, Martens. 1869. 



Columellar margin smooth. Rib of the operculum deeply furrowed, 

 multilobate at the tip, deeply excavated beneath. Terrestrial. 

 N. CORNEA, Linn. 



Inhabit damp foliage, Philippines, etc. 



Section THEODOXUS, Montf. 1810. 



Transversely globose, smooth or nearly smooth, columellar mar- 

 gin smooth. The claviform apophysis of the operculum distinct, 

 the apical apophysis rudimentary. Fluviatile. Inhabits mostly 

 rivers of Europe and Western Asia. 



