350 THE SEAS 



exchange, the shells varying in value according to their 

 size, and other shells have been similarly used in various 

 regions. 



At the present day certain shells are of considerable 

 commercial value as the source of the mother-of-pearl 

 used for the manufacture of such articles as buttons, studs, 

 knife handles, brooches, fans and all manner of inlaid 

 work. The shells principally employed are those of the 

 large pearl oyster, Margaritifera, and the large Trochus 

 (a tropical variety of the common top shells of our 

 shores). There are important fisheries for the former in 

 the Persian Gulf, the Red Sea — where the shells were 

 artificially cultured on a large scale until the slump after the 

 war rendered this unprofitable — the Great Barrier Reef of 

 Australia and the Torres Straits between Queensland and 

 New Guinea, Thursday Island being the headquarters of 

 this fishery, and also the Pearl Islands in the Bay of Panama 

 and various other regions in the Indian and Pacific oceans. 

 The thick mother-of-pearl which lines the inner surface of 

 the shell (formed as we have just seen, of the same substance 

 as pearls) is cut out (Plate 123) by machinery and then 

 worked up into the desired shapes. 



Among the many shells used for decorative purposes we 

 may perhaps mention one, known in the Channel Islands 

 as the Ormer and on the Pacific coast of North America 

 as the Abalone, the scientific name being Haliotis (Plate 121). 

 This is really a large, very flattened limpet with a shell 

 perforated by a curved row of openings. When cleaned 

 and polished it is a very beautiful object and is frequently 

 used in shops as a shade for electric lights. The flesh, 

 incidentally, is edible and highly prized in many parts, 

 especially in the United States where the canning of the 

 flesh forms a considerable industry. 



