138 



NERITIDJE. 



Shell semiglobiilar or semioval, flat underneath, with- 

 out umbilicus : aperture half divided transversely, 

 and furnished with an operculum. 



XXVI. NERITINA. 



Shell solid, semiglobular or semioval, flat underneath, 

 with a very short lateral spire : aperture entire, 

 semicircular or semielliptic, with an operculum ; 

 pillar sharp-edged, placed transversely in a straight 

 line, without teeth : umbilicus none. 



This Genus has been separated from the Nerita, the 

 species of which are all marine, with the pillar 

 placed more obliquely ; and from the Natica, also 

 a marine tribe, furnished with an umbilicus. 



124. Neritina JluviatUis. Shell convex, dilated, 

 tessellate with variously coloured spots. 



Neritina fluviatilis. Lamarck, vi. ii. j^, 188. 



