186 BIVALVES. 



side where it is straight and transverse ; surface 

 imbricated with transverse membranaceous 

 scales, having the laminae toothed in rays ; colour 

 commonly greenish or pale chestnut, inside 

 pearly and iridescent ; the full grown shells are 

 sometimes ten or twelve inches long and rather 

 less in breadth : they are thick and ponde- 

 rous, but young specimens are thin, brittle, and 

 slightly eared. 



This species is much celebrated for producing 

 pearls, a calcareous substance similar to that of 

 the shell itself, and arranged in concentric layers. 

 Acids have the same effect upon pearls as upon 

 other carbonates of lime, and Cleopatra is said to 

 have dissolved in vinegar one of great value in 

 order to display her magnificence by this costly 

 draught. The pearl fishery is a very dangerous 

 employment ; it is principally carried on in the 

 Persian Gulf and the neighbourhood of Cey- 

 lon ; the season for the fishery lasts about a fort- 

 night. Numerous boats are despatched to the 

 station where it is carried on, each containing 

 twenty men, ten of whom are employed in row- 

 ing and assisting the divers. They descend 

 alternately in parties of five, and thus time is af- 

 forded for all to recover themselves after their 

 violent exertion. The diver has a rope attached 

 under his arms, the end of which is given to the 

 men in the boat ; round his neck is slung a net, 

 distended at the opening by a hoop. Closing 

 his nostrils, he commits himself to the sea, with 

 a perforated stone often or twenty pounds weight 

 affixed to his foot, to accelerate his descent. He 



