214 HALF AN HOUR WITH SHELL-FISH (BIVALVES). 



it formerly belonged, and it is not difficult to 

 imagine the fearful storm that broke her to pieces, 

 and perhaps consigned her gallant crew to a watery 

 grave ! That piece of wood has probably been cast 

 to and fro for weeks, before it reached this settle- 

 ment. In the meantime, marine animals, sea-worms, 

 Fi 116 zoophytes, &c., have an- 



chored themselves to it. 

 But what is most striking, 

 perhaps, is the manner with 

 which it is perforated, evi- 

 dently by worm tubes. For 

 a long time, the creatures 

 which bored these tunnels 

 were believed to be worms, 

 and to this day they go by 

 the popular name of " Ship- 

 worms " (Teredo navalis). 

 They are molluscs, however, 

 and bivalves, although the 

 two shells, being small and 

 by no means able to cover 

 the soft body of the animal, 



Pholas dactylus. , , , 



were formerly regarded as 



the jaws of the worm ! Each of the tubes is lined 

 with a thin layer of shelly matter. ~ 



Boring mollusca are tolerably plentiful in our 

 seas. Perhaps the principal kind is the Pholas 

 (Fig. 116), whose brittle, roughened, white shells you 

 may frequently see thrown on the sands. Or, if 



