486 THE AQUARIAN NATURALIST. 



its vast ruins, apparently still imperishable, but which 

 melt away in time, as though they were but frag- 

 ments of an iceberg. 



Rare, and sometimes welcome to the sight of the 

 poor sailor, weary and tempest-tost, is the casual 

 appearance of a drifting tree, which tells him generally 

 that land is somewhere near ; and yet, when we reflect 

 what endless stores of floating timber every year roll 

 down from the wild forest regions of both hemi- 

 spheres, it becomes an interesting question how the 

 wide ocean is kept clear from the accumulation of 

 such obstructions. 



Various are the agents silently at work, whose 

 energies are specially devoted to this important 

 service. The Pholades and Saxicavae mine the solid 

 rock as efficiently as the sappers employed at Se- 

 bastopol; while floating timber, vanishing more 

 speedily, proclaims how easily, and yet how well, the 

 " gimlet-mouth' d Teredo" does its duty. The truth 

 is, that a whole army of miners is organized for the 

 above purpose, which, under the general name of 

 Pholas, have, from a very remote period, excited the 

 attention of the natural historian, and even at the 

 present day are very puzzling subjects for contem- 

 plation. 



The word Pholas is derived from the Greek <a>Xe&>, 

 and signifies simply anything that is hidden ; the 

 name having been given to this genus of shell-fish 

 from their custom of making for themselves holes in 

 mud, clay, or other substances, and living in them 

 hidden from observation ; habits which, as may 

 readily be supposed, necessitate important modifica- 



