240 MONOMYARIA.—AVICULADZ, 
Pearls are indeed produced by several genera of 
shells both bivalve and univalve, but the most 
precious are obtained from the species named 
Avicula margaritifera, which is a native of the 
Indian Ocean. On the coast of India and Persia 
numerous fisheries are established, which supply 
the markets of the world with precious pearls. 
Some of these have been carried on from very 
AVICULA. 
ancient times; that for example at Catifa in Arabia, 
which produced the celebrated pearl bought by 
Tavernier for 110,000/., is mentioned by Pliny. 
The most productive fisheries are prosecuted in 
the Persian Gulf, and on the coast of Ceylon; that 
of the Bahrein Islands, in the former locality, often 
produces pearls to the value of 90,0002. sterling in 
two months, the time in which it is prosecuted. 
This is free to all adventurers on payment of the 
