64 THE HALL OF SHELLS. 
“The pearl oyster which produces the finest 
pearls of all the pearl-growing bivalves is 
found at considerable depth im 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 pear! fish- 
erles of the Persian Gulf 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 which are often two feet long; the best 
known variety is the P. nobilis, 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 
FHlaliotide, 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 
