4o8 The Commercial Products of the Sea. 



It was long supposed that pearls were only formed in 

 bivalve shells, and it was therefore difficult to understand 

 what shell it was that yielded the pink pearl, for no known 

 bivalve of any size has such a coloured inner surface. It 

 is now ascertained that the pink pearl is produced, among 

 others, by one of the porcelaneous or chank shells (Tur- 

 binella scolymus). All doubt on this head is set at rest 

 by a specimen of this shell in the British Museum, where 

 a fine large pink pearl has been caught and embedded in 

 the shell, near its aperture, just as it was about to escape. 

 The pearl is exactly like the internal surface of that shell. 

 These pink pearls are also produced- by the common 

 fountain-shell of the West Indies {S trombus gigas), and 

 are known in commerce as conch pearls. Some very fine 

 pink pearls were shown from the Bahamas at the London 

 International Exhibition of 1862. These pearls, however, 

 fade, as do the pink cameo brooches. The giant clam 

 {Tridacna gigas), the common oyster {Ostrea edulis), the 

 horse-mussel {Modiola vulgaris), and many other bivalves, 

 yield pearls, but they are generally opaque and valueless. 



Small seed-pearls are obtained in the Eastern seas from 

 the semi-transparent molluscous shell, Placuna placenta or 

 orbicularis, and are chiefly used for medicinal purposes in 

 China. Some of the finer ones are selected as jewellers' 

 pearls, but these are of a different character and lustre to 

 the pearls produced by the Avicula margaritifera and the 

 Meleagrina margaritifera, which is abundant in the Sulu 

 Archipelago. 



Although pearls are obtained in the seas and rivers of 

 many parts of the world, yet the fisheries have been prose- 

 cuted on a large scale, for the purposes of commerce, in 

 only three or four localities — in the Gulf of Manaar, on 

 the pearl banks of Ceylon, Aripoo, and Tuticorin in 



