ference : aperture transverse, oval, with the margin 

 spread and united all round : operculum none. 

 Type. Helix Lapicida, Montagu. 



10. AzECA. Shell subcylindrical, rather obtuse : 

 aperture pear-shaped, curved and pointed at top ; 

 the margin thick, obtuse, and united all round : 

 operculum none. 



Tyj^e. Turbo tridens, Montagu. 



11. Clausilia. Shell reversed, turrited, spindle- 

 shaped, obtuse : aperture oval, oblique, toothed : 

 the margin obtuse and united all round : operculum 

 internal, spiral. 



Type. Turbo bidens, Montagu. 



12. BuLiMUS. Shell oval or oblong, pointed : aper- 

 ture longitudinal, oval, entire ; the margin disu- 

 nited at top : pillar smooth, simple, rounded and 

 entire at the base : operculum none. 



Type. Helix obscura, Montagu. 



