128 GENUS XXIX. HELIX. 



Trochi, as Labio, Lis, &c. : and Turbo, as littoreus, PuUus, 

 &c. 



The general form of these shells is very various ; many ap- 

 proach the shape of a globe, as nemoralis ; some are fiat and 

 wheel-shaped, as Vortex ; others are cylindrical, as octona ; 

 others depressed, much like to Trochus Solaris, as Carocolla ; 

 some tapering, as stagnalis ; and others somewhat ear-shaped, 

 as Auricularia ; or even flat, as haliotoidea (/. Ill): in most 

 species the mouth is without teeth ; but there are many that 

 have teeth, as H. sinuata (f. 1 13), &c. H. Scarabceus has teeth 

 also, but is set down as doubtful by Linnaeus, and seems not 

 to have any relation to the rest of the genus. 



Linnaeus makes six divisions of this genus : first, Ancipites ; 

 second, Carinatee ; third, Rotundatee umbilicatcB ; fourth, Ro- 

 tundatce imperforatce ; fifth, Turritee ; and sixth, Ovatee imper- 

 forate. 



The animals of the land species are supposed nearly to re- 

 semble the common Garden Snails, or Helix nemoralis and 

 hortensis ; some of them are described by different authors, 

 but many are not known. It is probable there are many va- 

 rieties among the water species ; H. vivipara and tentacidata 

 have horny opercula, which is supposed not to be the case 

 with any others of this genus. 



The animal inhabiting H. janthina is different from all 

 that are known of the others ; it swims at liberty in the sea, 

 and has four horns or awl-shaped tentacula ; it has instead 

 of a foot a membranous transparent lump, which it swells 



