an operculum, spiral, often ornamented externally 

 with striae or slight ribs ; the outer margin of the 

 aperture sometimes expanded or reflected. 



* with four distinct tentacula. 7 — 15. 



** with two of the tentacula very short or obsolete. 

 16, 17. 



t Bulimus lineatus. 



7. ViTRiNA. Shell extremely thin and transparent, 

 glass-green : spire very short and flat : aperture 

 ample, elliptic ; the margin disunited at top : um- 

 bilicus none : operculum none. 



Type. Vitrina pellucida, Draparnaud, p. 119. 



8. Helix. Shell orbicular, conoid or a little flat- 

 tened, obtuse : aperture transverse, oblique, semi- 

 oval or lunate ; the margin disunited. 



Type. Helix aspersa, Montagu. 



9. Carocolla. Shell orbicular, depressed, gradually 

 sloping to an edge on both sides in its outer circum- 



