THE INDIAN OCEAN. 865 
Among the sea-shells which attain a large size in 
these seas, the Giant Clamp (Ziidacne 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 astrong 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 ages, 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 
2H2 
