310 PKOCEEDINGS OF THE MAIACOLOGICAL SOCIETY. 



distances from the edge of the aperture. As appears to be invariably 

 the case in the genus, it is pure white and porcellanous, and the 

 inner surface is coated with a mucous film which has quite a white 

 pearly lustre. The slit is situated at the upper, or posterior, end, and 

 looks exactly as if a knife had been thrust through from the outside 

 so as to force the substance out into a ridge, which is slit down the 

 middle, on the under surface. This slit is all but closed ^ in both of 

 the specimens examined. Such a solid structure as this would largely 

 help to prevent evaporation during periods of great heat and dryness, 

 thus retaining within the shell the moisture so necessary for the life 

 of the inhabitant. It would equally serve as a defensive barrier 

 against insects and other enemies during these seasons of torpidity. 



The use of the slit during aestivation, when life is almost suspended, 

 is doubtless for the purpose of conveying air for respiration, although 

 the breathing orifice is probably all but closed at such times. An 

 examination of a retracted animal reveals a slit-like opening in the, 

 mantle leading to the respiratory orifice which would receive the 

 perforated ridge on the epiphragm. 



The epiphragm of Helix pomatia and of S. aperta does not appear to be 

 perforated. 



