270 



CONCHIFEKA. 



for themselves tlie dens in which they reside, in stone, 

 clay, wood, or other substances, and in these exca- 

 vations they live a sedentary life. Their shell is 

 generally thin and brittle, but it is extremely hard, 

 and covered externally with file-like teeth, that 

 seem to constitute the tools employed in their boring- 

 operations. 



The Ship-worm {Teredo)* well characterized by 

 Linnaeus as the "' calamitas navium," seems to have 

 been specially appointed by Providence for the re- 

 moval of floating timber, which otherwise, by its 

 accumulation, might impede the navigation of the 

 sea. The mantle is excessively lengthened into a 

 sort of tube, while the valves are minute, so that 

 the appearance of these bivalves is rather that of 

 a Worm than of a MoUusk. It bores holes in all 

 directions through wood lying in the sea, lining 



Fig. 207. — ship-worm and its shell. 



the interior of its excavations with a shelly crust. 

 The piles of piers and wharves, the o-ates of docks, 

 and the bottoms of ships are soon riddled and pierced 

 by these animals, insomuch that serious fears have 

 been more than once entertained for the safety of 

 * Tepeo), tereo, to bore. 



