THE INDIAN OCEAN. 3^5 



Among the sea-shells wliicli attain a large size in 

 these seas, the Giant Clamp (Tridacne gigas) stands 

 pre-eminent. It is found in abundance on the coasts 

 of Sumatra, as well as of other islands, attached 

 to the rocks by a strong cable. This, which is called 

 byssus, is formed of many tough threads, but slightly 

 elastic, spun by the animal, or rather, cast in a 

 mould thread by thread ; a glutinous fluid being 

 secreted in a long groove or canal formed by the 

 foot, which in the air rapidly acquires solidity. 

 When complete, the united threads form, as ob- 

 served above, a cable, projecting through an open- 

 ing in the back of the shell, and adhering by the 

 other extremity to the rock, so firmly as to resist 

 the agitation of the sea, and so tough as to be severed 

 only by an axe. Marsden mentions one which was 

 more than three feet three inches long and two 

 feet one inch wide : and specimens have been seen 

 which had attained the enormous length of four 

 feet. They are sometimes taken, when not adhering, 

 by thrusting a long bamboo between the open 

 valves, which immediately close firmly, and they are 

 dragged out. The substance of the shell is perfectly 

 white, several inches thick; and is worked by the 

 natives into arm-rings, and by European artists is 

 made to receive a polish equal to the finest statuary 

 marble. 



Pearls, whose exquisite beauty have made them 

 celebrated from the earliest asres, are well known to 

 be marine productions ; and as the shores of the 

 Indian Ocean yield the finest specimens, I may here 

 say a word of the fishery for them. Many bivalve 



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