60 HELICID-. 
largest of our land snails. The above term was applied 
to it under the misapprehension that pomatia was derived 
from the Latin Aomum, an apple, whereas it is from the 
‘Greek oma, an operculum. It has no true operculum, 
but, when retiring into winter quarters, forms a very thick 
epiphragm from a secretion of the mantle, which hardens 
on exposure to the air like plaster-of-Paris. _ When this 
thick plate closes the entrance, the animal retires deeper 
into the shell and fortifies itself still further against the 
cold by a succession of thin films. 
Whether this snail was introduced by the Romans as 
an article of food is doubtful; at any rate the 
coincidence of its local and restricted range in the 
vicinity of Roman military stations and villas is very 
striking, and Mr. B. B. Woodward (Proc. Geol. Mag., 
August, 1890, ‘ Mollusca of the London district,” says, 
“ FT, pomatia and HH. aspersa are not found anywhere in 
pre-Roman deposits, though frequently found with 
Roman remains.” 
Jeffreys argues against the theory of its Roman intro- 
duction on the ground there are several such localities 
where it does not exist, which negative evidence is hardly 
‘convincing, especially as regards the northern places he 
instances (York, and Wroxeter near Shrewsbury), where 
ithe colder climate might be expected to disagree with its 
southern constitution, and the soil is notcalcareous. Jeffreys 
also points out that the shell has not been found in any 
