30 



HELICID^E. 



Body a spirally twisted slug. Shell spiral, with or 

 without an operculum, generally thin, and armed 

 externally only with striae or slight ribs : aperture 

 never emarginate at the base nor reflected back, 

 with the outer margin sometimes expanded, or re- 

 flected. 



7. Vitrina. 



8. Helix. 



9. Carocolla. 



10. Azeca. 



11. Clausilia. 



12. Bulimus. 



13. Balsea. 



14. Achatina. 



15. Succinea. 



16. Cyclostoma. 



17. Carychium. 



VII. VITRINA. 



Shell oblong, extremely thin, brittle and transparent, 

 with a slightly raised obtuse spire, consisting of 

 two or three volutions, the outer one extremely 

 large. Aperture ample, elliptic, wider than it is 

 high, interrupted by the second volution, without 

 operculum ; umbilicus none. 



A Genus very nearly allied to the Helix, but distin- 

 guished by its oblong or semi-elliptic figure and 

 its large produced aperture. 



