GASTEROPODA PECTINIBRANCHIAT A. 249 



It is here that we must place the completely aquatic shells, or those respiring 

 by branchiae, which belong to the old genus, HELIX ; i. e. those in which the 

 penultimate whorl forms, as in the Helices, Lymnaeae, &c., a depression 

 which gives the aperture more or less of the figure of a crescent. 



The three first genera are still closely allied to Turbo. 



PALUDINA, Lamarck. 



This genus has lately been separated from the Cyclostomae, because there 

 is no ridge round the aperture of the shell ; a small angle to that 

 aperture as well as to the operculum ; and finally, the animal, being 

 provided with branchiae, inhabits the water, like all other genera of this 

 family. It has a very short snout, and two pointed tentacula ; eyes at the 

 external base of the latter, but on no particular pedicle, and a small membra- 

 neous wing on each side of the fore part of the body. The anterior edge of the 

 foot is double, and the wing of the right side forms a little canal which intro- 

 duces water into the respiratory cavity, the incipient indication of the siphon 

 in the following family. 



The ocean produces some shells which only differ from the Paludinae in 

 being thick. They form the 



LITTORINA, Ferussac, 



Of which the common species, Le Vigneau Turbo littoreus, Lin., abounds on 

 the coast of France, where it is eaten. The shell is round, brown, and longi- 

 tudinally streaked with blackish. The 



PHASIANELLA, Lamarck. 



An oblong or pointed shell, similar to that of several Bulini and Lymnaeae ; 

 the aperture also higher than it is wide, and furnished with a strong oper- 

 culum ; base of the columella sensibly flattened, but no umbilicus. 



They inhabit the Indian Ocean, and are much sought for by collectors on 

 account of the beauty of their colours. The animal is provided with two long 

 tentacula, with eyes placed on two tubercles at their external base, and 

 with double lips that are emarginated and fringed, as well as the wings, 

 each of which has three filaments. 



AMPULLARIA, Lamarck. 



A round, ventricose shell, with a short spire, as in most of the Helices ; the 

 aperture higher than it is wide, and provided with an operculum ; the colu- 

 mella umbilicated. 



They inhabit the fresh or brackish waters of hot countries. The animal 

 has long tentacula, and eyes placed on pedicles at their base. 



HELICINA, Lamarck. 



Judging by the shell, the Helicinae are Ampullariye in which the margin 

 of the aperture is reflected. 



