and on the removal of portions of their Shells. 247 



of the mollusks. In all the boring species I have endeavoured 

 to show that the foot and mantle are the organs employed ; and 

 that in Patella, with which the analogy may be considered 

 closest, the mantle is highly instrumental. In this species we 

 have seen that it has the power of rubbing down shale, limestone 

 and shell; and these substances are removed as the shell in- 

 creases, apparently for the purpose of levelling the surface, and 

 preparing it for the accommodation of the animal. The mantle 

 oiBuccinum undatum and of many other Gasteropods does — what ? 

 It clears away obstructions from the columella and reduces its 

 thickness, that as the animal grows it may have sufficient room. 

 They all, Acephala as well as Gasteropoda, rub down those hard 

 substances only during growth, and all do so that they may find 

 increased protection and accommodation : it is the same act in 

 all, the same organ is employed in all; and we can scarcely 

 doubt that in all it is furnished with the same means. 



We might have gone more fully into this branch of the sub- 

 ject, but it appears unnecessary to do so ; for if I have succeeded 

 in substantiating my views in the former part of this communi- 

 cation, little need be said here ; if not, all that I could now ad- 

 vance would be of little service, feeling strongly inclined to be- 

 lieve that one law regulates the whole of these phenomena. 



The boring of the carnivorous Gasteropods, into bivalve and 

 other shells, remains yet to be examined; but having already 

 extended this paper to too great a length, this interesting portion 

 of the subject cannot now be fully entered upon. In reference 

 to it I shall at present make only one or two remarks before 

 concluding. 



A short time ago Mr. Richard Howse discovered Purpura 

 boring on the Durham coast, and in company with that gentle- 

 man I have had several opportunities of taking this animal in 

 the act of piercing the common Mytilus, which appears to be a 

 favourite food. The holes are generally one-sixteenth of an inch 

 in diameter, being just sufficient to admit the proboscis, which 

 in one or two instances I have seen inserted in the bore. The 

 tongue, which is covered with transverse rows of siliceous spines, 

 is strap-formed and very long; it is much narrower than the 

 bore ; and the anterior spines are generally worn down, or have 

 never been developed. The bores are for the most part circular, 

 sometimes they are slightly oval, and frequently pass through the 

 epidermis, which in Mytilus is strong and horny. When they 

 do so the epidermis is never torn, but the edges are smooth and 

 circular like the rest of the bore. 



Putting these facts together, it is, perhaps, fair to conclude 

 that the boring in this case is also mechanical, and that the 

 tongue is the instrument, though it is difficult to understand 



