13. Bal^a. Shell reversed, turrited, pointed : aper- 

 ture oval, entire and rounded at the base ; the mar- 

 gin disunited at top : pillar with mostly a single 

 tooth : operculum none. 



Type. Turbo perversus, Montagu. 



14. AcHATiNA. Shell oval-oblong, obtuse : aperture 

 longitudinal, oval, entire ; the margin disunited at 

 top : pillar smooth, simple, truncate at the base : 

 operculum none. 



Type. Buccinum terrestre, Montagu. 



15. SucciNEA. Shell oval-oblong, thin ; the spire 

 very short and conic, with the lower volution very 

 large : aperture ample, longitudinal, oblique ; the 

 margin disunited at top : umbilicus none : opercu- 

 lum none. 



Type. Helix putris, Montagu. 



16. Cyclostoma. Shell conic-oval : aperture orbi- 

 cular, without teeth ; the margin united all round : 

 operculum with a single depressed spiral line. 

 Type. Turbo elegans, Montagu. 



