GEiVUS XXIX. HELIX, 1^29 



out at pleasure into a heap of little bladders, and w iiich at-sit^ts 



it in swimming. 



Linnaeus describes 59 species, Gmelin has added 169, and 



Dr. Turton 26. Total, 253. 



Lamarck divides this genus into eight, as follow : 



Janthina. Shell nearly globular, transparent ; the aperture 

 triangvdar, with an angular hollow or notch on the margin 

 of the right lip (^see Helix Janthina, pi. 8. /. 107). 



BuLiMUS. Shell oval or oblong, having the last whorl of 

 the spire larger than the former ; the aperture entire; 

 longer than it is broad ; the pillar smooth, the base entire 

 and not spread out (see Helix oblonga, pi. 8. /. 108). 



Lymnjea. Shell oblong, rather tapering ; the aperture entire, 

 longer than wide; the lower part of the right lip re- 

 ascending and turned back into the aperture, and form- 

 ing a very oblique fold on the pillar (see Helix stagnalis, 

 pi 8. /. 109). 



Melania. Shell turrited ; aperture entire, longer than wide, 

 and spreading at the base of the pillar, which is smooth 

 (see Helix Amarula, pi. 8. /. 117). 



AaiPVLLARiA. Shell globular, ventricose, umbilicated at the 

 base ; the aperture entire and longer than wide, without 

 any thickening on the left lip (see Helix ampullacca, 

 pi. 8. /. 1 12). 



Planorbis. Shell wheel-shaped; spire not projecting, flal- 

 lened or sunk in ; the aperture entire, longer than \\ ide, 



s 



