8 NERITIDiE. 



ellar lip usually finely denticulated, often with a large sujDerior 

 tooth. Operculum with rib and apophyses well developed, the 

 latter connected for half their length. 



The spines that usually ornament the whorls are tubular, and 

 sometimes very long. They are fluviatile and tropical, crawling 

 slowly, and only showing during locomotion the tentacles and tip of 

 the muzzle ; they seem to prefer a stony bottom, clear and free from 

 weeds, and quiet Avater. N. longispina, Recluz, 



Subgenus Neriptekon, Lesson. 1830. 



Shell flattened, biauriculated posteriorly, spire posterolateral ; 

 inner lip septiform, with non-denticulated margin, outer lij^ very 

 much dilated behind. Operculum typical. Fluviatile. Polynesia. 

 N. Tahitensis, Lesson. 



Section Alixa, Recluz. 1842. 



Shell flattened, transversely dilated, lip irregularly expanded, 

 sinuous, margin of inner lip finely denticulated. Operculum typi- 

 cal. Fluviatile. Central America. JST. latissima, Brod. 



Subgenus Dostia, Gray. 1840. 



Shell sandal-shaped, solid, the apex completely posterior and a 

 little lateral ; peristome continuous and free ; inner lip septiform, 

 arcuated and denticulated in the centre of its margin. Operculum 

 typical. Brackish water. Ea.st Indies. N. crepidularia. Lam. 



Genus VELATES, Montfort. 1810. 



Oval conic, spiral at the apex only ; last whorl greatly enlarged, 

 resembling Trochita externally ; aperture basal, semicircular, its 

 margin forming with that of the wide, flat columellar lip a circular 

 outline, columellar margin dentate. Operculum as in Neritina. 



Tertiary of Europe, India, Madagascar, etc. V. perversa, 

 Linn. (Struct, and Syst. Conch., t. 78, figs. 81, 82). 



Young individuals are Neritiniform, and the apex is completely 

 lateral. 



Section Velatella, Meek. 1878. 



Shell small, oval; apex posterior, spiral, dextral, submedian. 

 V. CARDiToiDES, Meek (Struct, and Syst. Conch., t. 78, figs. 85, 86). 

 Laramie formation, N. America. 



