64 THE HALL OF SHELLS. 



" The pearl oyster whicli produces the finest 

 pearls of all the pearl-growing bivalves is 

 found at considerable depth in large shoals 

 in the Indian Ocean, Gulf of Persia, some parts 

 of the Pacific Ocean, etc. About thirty thou- 

 sand people find employment in the pearl fish- 

 eries of the Persian Grulf alone. 



" As many as one hundred and fifty pearls 

 have been gathered from a single shell. 



"Among the other bivalves producing 

 pearls is the Pinna or wing-shell, the valves 

 of vphich are often two feet long; the best 

 known variety is the P. nohilis, which inhabits 

 the Mediterranean, and is especially curious on 

 account of its byssus. 



"Another singular variety is the ham- 

 mer oyster — Malleus vulgaris — whose ham- 

 mer-shaped shell is beautifully laminated with 

 mother-of-pearl. 



" But Tom must hear about his beautiful 

 abalones," said the doctor, seeing he held sev- 

 eral in his hands. 



" This rainbow shell belongs to the family 

 HaliotidcjB, of which there are many species, 

 named according to their slight variations and 

 the localities which they inhabit. 



"Abalone — the name which we upon this 

 California coast familiarly use — is a name the 



