26 THE SHELL-FISH OF THE COAST. 



bushels per week duriDg the months of March to 

 August inclusive, and 500 hushels 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 he said eii 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 



