CARNIVOROUS MOLLUSCS 



97 



of the aggressors actually at work. The rasping noise made by the 

 radula as it bores through the barnacle's shell is readily audible. 



Fig. 378. — The Purple-Shell {Purpura la^ilhis). The small figure shows an individual crawling. 



Another common carnivorous sea-snail, much larger than the 

 Purple-Shell, and rapacious in proportion to its size, is the 

 Common Whelk {Buccinum undatum) (see vol. i, p. 321), 

 abundant in shallow water. The rasping apparatus is 

 lodged in the tip of a very long narrow proboscis, which 

 can either be protruded or drawn completely back into 

 the body. Whelks chiefly prey upon bivalve molluscs, 

 even some of the burrowing species not being exempt 

 from its attacks, and it is one of the many enemies of 

 the oyster. 



The Cone -Shells, most of which are tropical, are 

 interesting in the present connection because the bite is 

 poisonous in some, perhaps all, of the species (fig. 379). 

 That any sort of sea-snail should bite a human being 

 seems at first sight somewhat singular, but Cone -Shells, 

 when incautiously handled, have done so, and this led 

 to the discovery that some of these forms are poisonous. 



Method of Shell-boring. — Such molluscs as the Purple- 

 Shell, Whelk, &c., are commonly supposed to depend 

 entirely on the radula as a means of penetrating the shells of their 

 victims. It certainly does assist in the process (see above — Purple- 



F!g. 379 

 Barbed 

 Poison-tooth 

 from radula 

 of a Cone. At 

 the base is 

 seen the poi- 

 son-gland, 

 the duct of 

 which runs 

 within the 

 tooth and 

 opens near 

 its tip. 



39 



