NO. 51. — 1900.] PEARL FISHERIES. 



169 



consequently, their correct identification is a matter of con- 

 siderable difficulty. We find, for instance, quite a number of 

 shells — bearing both pearls and mother-of-pearl — designated 

 by the common name of M. margaritifera ; whereas, in all 

 probability, they belong to very distinct species. True, M. 

 margaritifera (the mother-of-pearl oyster) does frequently 

 produce pearls, but it differs in many important particulars 

 from the other pearl-bearing species of Meleagrina— the shells 

 of which are not, as a rule, of any value as mother-of-pearl. 



The geographical distribution of the pearl-bearing species 

 of Aviculidcs appears to be as follows : — 



1. Avicula {Meleagrina) margaritifera, Lin.— The large 

 tropical pearl oyster of Northern Australia, the Pacific, and 

 the South Seas generally. It is the mother-of-pearl shell of 

 commerce, and although it often contains pearls it is chiefly 

 fished for the sake of its shell alone. 



2. A. (M.) imbricata, Rve. — The pearl shell of the northern 

 coast of Western Australia. It is said to be closely allied 

 to the Panama species. It produces pearls, but its shell is 

 of little value. 



3. A. (M.) fimbriate/,, Dkr. — The pearl oyster of the Gulf 

 of California and the Bay of Panama. 



4. A. (M.) Martensii, Dkr. — The pearl oyster of the 

 Japanese Seas. 



5. A. (M.) fucata, Gould. — The pearl oyster of the Gulf 

 of Mannar. It also occurs in the Torres Straits and (proba- 

 bly) in the Arabian Seas.* 



* Mr. Holdsworth, the Naturalist engaged by the Ceylon Government 

 in 1867 to investigate the pearl oyster question (but who unfortunately 

 never had an opportunity of seeing a fishery, and, according to Sir William 

 Twynam, never saw a pearl bank with oysters on it), was the first to point 

 out the distinction between the Gulf of Mannar oyster and that of the 

 Persian and Arabian Seas (JPlacuna placenta'). Some shells from the 

 Persian G-ulf shown to Captain Donnan appeared to him to exhibit no 

 differences from the Mannar species [ " Gold, Gems, and Pearls," p. 374] — 

 from which I conclude, having regard to his (Captain Donnan's) great 

 experience, that the Mannar oyster also occurs, though perhaps sparingly ? 

 in the Arabian Seas ; and this may account for the occasional discovery of 

 fine " Oriental " pearls in that region. 



