MOLLUSCA, THE SHELL-FISH 103 



lations file away much harder things. A Sting- 

 winkle, or a Dog-whelk, can sit down over a help- 

 less bivalve shell-fish, and patiently file away, until 

 it has worked a neat round hole in the protecting 

 shell of the latter. You may find, among the dead 

 shells on any sandy part of the English coast, any 

 number of bivalve half-shells with a neat little 

 round hole in them, indicating unmistakeably how 

 the tenant came to its death. There is some con- 

 troversy as to the spot chosen by the assailant for 

 its attack. Some authorities have stated that the 

 predatory mollusc is so wise that it knows where 

 to find a weak spot, and makes a hole just over 

 some vital organ of the bivalve, or else above its 

 adductor muscles, so that, when these are cut, 

 the half-shells cannot be drawn tightly together 

 and kept shut. Recently this has been denied, 

 and statistics of the attacks of Purpura, the com- 

 mon small whelk, a relation of the Murex, on 

 Myttlus edulis, the Common Mussel, have shown 

 that the perforation occurs in every part of the 

 shell. It is possible, however, that the Mussel, 

 from the peculiar shape of its shell, offers an ex- 

 ceptional case; and I am inclined to think that 

 in the case of bivalves of a more flattened shape, 

 the earlier statement holds true. At South Shields, 

 England, perforated half-shells of the Common 

 Venus (Fig. 34) are so abundant that the children 

 string them for necklaces ; yet I have never been 

 able, by the most industrious search, to find more 

 than one or two specimens in which the hole is 

 at all near the lip of the shell. It is possible 

 that these exceptional instances were the work of 

 a young and inexperienced univalve mollusc, or a 

 stupid one. It is possible, also, that the mode of 

 attack differs somewhat according to the species 



