MOLLUSCA. 75 



sized sieves made of brass. The largest and handsomest, 

 called round pearls, are the most valuable, and sold ac- 

 cording to their weight, a single one, weighing but a 

 grain, is sold for a rix dollar (four shillings and sixpence 

 sterling).* The price varies according to their size ; ten 

 thousand rix dollars are sometimes demanded for the 

 largest. 



There is some labor expended on them before they are 

 ready for sale ; many washings are necessary to purify 

 them, and after being thoroughly cleansed they are pol- 

 ished with salt and tripoli, or sulphate of potash. The 

 divers are subject not only to the dangers of the deep, to 

 tempests, to suffocation at the bottom, to being devoured 

 by sharks, but also to severe disease arising from their 

 unhealthy employment of assorting the pearls from the 

 putrid oyster, and few survive more than five or six 

 years. 



This class of mollusca furnishes not only pearls as 

 worn for ornaments, but also mother-of-pearl formed 

 from the beautiful nacreous lining of the shell, and the 

 iridescent substance found at the clasp which is known 

 by the name of the Peacock Stone. 



The PinncB (pinna nobilis) are a span long; have 

 valves in the form of a half-open fan ; about a hand- 

 breadth across ; brown outside, but pearl-like within. 

 They have a foot with which they are supposed to spin the 

 filaments by which they anchor; these threads, termed 

 byssus, or by some beards, are often a foot in length ; 

 are strong and brilliant, partly of a gold color, and partly 

 brown. The animal thrusts the sharp end of its shell into 



* The revenue of the pearl-fishery of Ceylon amounts annually to 

 $80,000. RUSCHEN YOT. Tr. 



