Marine Animals. 271 



fcmct. Being an imported animal, and from a warmer climate, 

 the change of temperature, Mr Osier thinks, has effected this, 

 in conjunction with the very prevalent use of copper for sheath- 

 ing vessels. 



But while Mr Osier proves that the Pholas and Teredo 

 perforate their dwellings by mechanical action alone, he is 

 of a different opinion with regard to other species of Li- 

 thophagi. " If all the boring shell-fish (he says) penetrate 

 mechanically, it would be reasonable to expect, that their 

 powers should evidently be in proportion to the hardness of 

 the bodies which they inhabit : this is found to be the case in 

 the different species of Pholas ; but the Lithophagi, which 

 would have the greatest mechanical resistance to overcome, ap- 

 pear to be destitute even of the smallest mechanical force. 

 They have nothing which in the slightest degree resembles the 

 boring apparatus of the Pholas. On the contrary, their shell, 

 as in the bimusculous conchiferae, is expanded by a powerful 

 elastic ligament, and closed by two large round internal ad- 

 ductors. The valves in most of the species shut close, and 

 the foot is not an instrument adapted for firm adhesion.*" 



Mr Osier goes on to state, that, in the neighbourhood of 

 Swansea, where his observations were made, four species of 

 Lithophagi are found ; and that, from particular attention to 

 the habits of one of these, the Saocicava rugosa (Mytilus ru- 

 gosus of Lin.) he has come to form the opinion, that they 

 must form their burrows in the rocks which they inhabit by 

 means of some solvent secreted by the animal. 



In the first place, he says, it is evident that this animal does 

 not bore like the Pholas, for its hole is not quite round, and 

 the animal of course cannot turn itself in the burrow. 2. That, 

 being attached by a short byssus, its free motions are in part 

 prevented. 3. That the foot of the animal is not an instru- 

 ment sufficiently powerful to effect this purpose. 4. That 

 the texture of the shell is so soft, that it could make no im- 

 pression on the stone without being itself acted on ; and the 

 effect of this would be permanent, because superficial injuries 

 of the shell are never repaired. 5. The absence of any ar- 

 rangement of muscles which might employ the shell with effect, 

 even were it strong enough to act on hard stone. And he 



