CONCHOLOGY. 107 



2. Genus A^erita. PI. X. 

 Animal. See Neritina. 



Shell. Marine, but never spined, solid, semiglobular, flattened 

 beneath, not inibilicated ; aperture large, entire, semilunar, the 

 external margin much hollowed, ; the columella sharp and often 

 dentated, operculum horny, subspiral, with a projecting tooth. 

 Inhabits the seas of S. x\merica and W. Indies. Twenty species. 



Nerita exuvia. Nerita lineata. 



N. textilis. N. scabricosta. 



N. undata. N. plicata. 



N. peloronta. N. tassellata. 



N. chlorostoma. N. signata. 



N. artata. N. ornata. 



N. polita. N. Australis. 



N. albicella. N. rudis. 



N. chamaeleon. N. Ascensionis. 



N. versicolor. N. Malaccensis. 



3. Genus J\''aviceUa. PI. X. 



Animal. Oval, not spiral, foot elliptical, very large, with a 

 thin subpapillary edge, advanced rather anteriorly, without mar- 

 ginal furrow, but attached on each side to the visceral mass in 

 all its posterior portion so as to form a sort of cavity open trans- 

 versely behind ; head very broad and semilunate ; tentacula 

 conical, contractile and distant; eyes subpedunculated at the 

 external root of the tentacula ; mouth large and longitudinal. 



Shell. Fluviatile, elliptical, or oblong, convex above, summit 

 straight, depressed to the margin, concave beneath, no columella, 

 the columellar edge replaced by a sharp partition, covering part 

 of the aperture ; a sinus of its left extremity ; muscular impres- 

 sion horse-shoe shaped, open in front and interrupted behind ; 

 thin calcareous operculum, with a sublate, lateral tooth adhering 

 to the posterior margin. Inhabits rivers in the Isle of France. 

 Four species. 



Navicella elliptica. Navicella lineata. 



N. tesselatus. N. porcelaniea. 



