NO. 51.-1900.] PEARL FISHERIES. 167 



scattered statistical reports issued from different pearling 

 stations. As a rule, these reports are drawn up for purely 

 commercial purposes, or with the object of laying down rules 

 and regulations for the conduct of the fisheries. Yet, here 

 and there, valuable zoological observations occur, by means 

 of which it is possible to form some idea of the biological 

 conditions which exist at different pearling centres. And 

 from such sources as these a great part of the material here 

 dealt with has been derived.* 



Varieties of Pearl Oysters. 



Pearls are produced by quite a number of different 

 molluscs, and some of these are very widely distributed. 

 Among the bivalves, the great Tridacna, the common oyster 

 {Ostrea edulis), and many species of Pinna produce pearls. 



They are also found in certain species of Unio and Ano- 

 donta — fresh-water shells — which furnish the river pearls of 

 Europe and North America. Certain univalve shells also 

 produce pearls, for example : — Strombus gigas, the giant 

 " conch-shell," and several species of Turbinella. These 

 produce the pink pearls of the Bahamas and of the West 

 Indies generally. 



The ordinary pearls of commerce may be divided, roughly, 

 into two classes, viz., false or " seed " pearls, and true or 

 " Oriental " pearls. The two kinds differ greatly both in beauty 

 and value, and are produced by two very distinct genera of 

 shells. These are (1) Placuna, with a single pearl-bearing 

 species, which belongs to the family of Anomiidce ; and (2) 

 Meleagrina, which includes several pearl-bearing species, 

 and which belongs to the family of Aviculidoe. 



* I take this opportunity of expressing my thanks to Mr. R. Etheridge, 

 the Director of the Australian Museum, Sydney, N.S.W., and to Mr. 

 Charles Hedley, the Conchologist of that Institution, for valuable reports 

 and statistics. Also to Professor H. A. Pilsbry, of the Academy of Sciences. 

 Philadelphia, U.S.A., and Mr. T. Nishigawa, of the Imperial Fisheries 

 Bureau, Tokyo, Japan, for information kindly supplied. Further, I am 

 under a special obligation to Mr. John Ferguson, of Colombo, who has 

 most kindly placed at my disposal a valuable collection of Papers relating 

 to various pearl fisheries. 



