26 THE SHELL-FISH OF THE COAST. 
bushels per week during the months of March to 
August inclusive, and 500 bushels per week for 
the remaining six months. At least 1000 persons, 
mainly women and children, were employed in the 
gathering. 
All the periwinkles are vegetable feeders, and 
are thus sharply defined in habit from the strictly 
carnivorous forms that have been thus far consid- 
ered. It may be said en passant that with compara- 
tively few exceptions all the snails whose shells 
have an even, round mouth are phytophagous in 
habit, living exclusively on vegetable substances, 
while those which have the shell aperture either 
truncated or produced into a canal of greater or 
less length are carnivorous. But both forms have 
the mouth provided with a peculiar chitinous or 
horny ribbon, known as the ‘lingual ribbon’ or 
‘radula,’ which is closely beset with minute teeth, 
and by its backward and forward movement serves 
to rasp down objects that are brought in its way. 
It thus largely assists in the process of mastication ; 
but probably one of its functions is the boring of 
the holes in ‘ foreign’ shells through which an at- 
tack is made upon the enemy. ‘The coiled lingual 
apparatus of the common European -Littorina litorea, 
which has also been introduced on the New Eng- 
land coast, measures two and a half inches in length, 
and contains about 600 rows of teeth. The action 
of this ribbon may be well observed in the case of 
snails that creep up the glass walls of aquaria. 
An exception to the rule which defines round- 
mouthed snails to be vegetable feeders is the 
