428 The Commercial Products of the Sea. 



frequently bring up about 30 Ibs. weight of shells after one 

 dive. The value of the shells in the colony averages from 

 7 t % P er cwt. These shells, the home of the Melea- 

 grina margaritifera, weigh on the average about two 

 pounds per pair, and measure from six to ten inches in 

 diameter. It is to their intrinsic commercial value, rather 

 than to the pearls they contain, that the north-west fisheries 

 owe their importance. 



Another lucrative fishery exists in Shark's Bay, a large 

 inlet, extending in a south-easterly direction from Dirk 

 Hartog's Island, about the twenty-fifth degree of south 

 latitude, to a distance of 150 miles. The shells found in 

 this region are those of the true pearl oyster, the Avicula 

 margaritifera, an oyster only slightly larger than its Euro- 

 pean congener, and valuable for the pearls it bears. The 

 shells themselves have no commercial value. 



A large pearl was found a year or two ago on the north- 

 west coast. It is pear-shaped, weighs 1 59 grains, is of a very 

 fine texture, and has an excellent lustre. Its size is about 

 equal to that of a common acorn, though it is of course 

 different in shape. There are one or two specks on the 

 smaller end, which is also scarcely perfect in its outline, 

 but the thick end is superb, and is not marred by the 

 slightest defect. No fair estimate of its value could be 

 made locally, as there is no Australian market for such 

 gems. The pearl was found by a pearling expedition fitted 

 out from the port of Melbourne. 



The subject of marine pearls can scarcely be dealt with 

 without a brief allusion to the river pearls which are 

 obtained from the Alamodon, Anodonta, Unios, and other 

 shells, in different countries. 



Many of the fresh-water mussels produce pearls in the 

 mountain-streams of Britain, Lapland, and Canada ; but 



