88 



This shell is local, though abundant where it occurs, 

 It is found on the bark of trees ; Dr. Jeffreys says 

 " chiefly the beech, ash, sycamore, and apple." I once 

 found it on a willow near Windsor, in company with 

 C. rugosa, the young of which it much resembles. 

 This resemblance it is necessary to draw attention to, 

 or this local species may be passed over. It differs 

 from the immature C. rugosa in being more slender, 

 lighter in colour, having a deeper suture, and being 

 without any carination along the basal ridge, which is 

 a marked characteristic of the young of that species. 



Var. viridula* Greenish white, transparent. 



Genus IX. CLAUSILIA^ 



This genus derives its name from a peculiar charac- 

 teristic a little door (L/at. elausilium). 



This interesting provision of nature against the 

 attacks of such enemies as beetles, &c., differs from an 

 operculum thus: It is not fastened to the animal, but 

 to the pillar of the shell by an elastic filament. When 

 the animal is within the shell this contractile filament 

 draws the elausilium close over the aperture, about 

 half a turn from the entrance, and when the animal 

 emerges it pushes aside the little " spring-door^" which 

 then lies flat against the columella. 



