140 The Under-Water World 



in a vitiated atmosphere and complete 

 darkness. 



The largest bivalve known is the Giant 

 Clam (Tridcena gigas) of the Barrier Reef, 

 which may measure over two feet in 

 length and weigh 500 Ib. This mollusc 

 is a veritable man-trap and the diver 

 putting his foot in the gap between each 

 valve is usually doomed. Not long ago 

 a native was caught by a baby giant 

 clam at low tide. Attempts to hack the 

 shell to pieces would have resulted in the 

 mollusc bringing the valves together 

 with such force as to crush the man's 

 limb to a pulp. Therefore to save his 

 foot a block of the coral, about three feet 

 square, to which the clam was attached, 

 was cut away and the native with the 

 block complete was placed on a stretcher. 

 The coral mass was then placed beside 

 a fire. Gradually the heat caused the 

 shell to open of its own accord and the 

 victim was liberated. This tendency on 



