CONCHIFERA. 



305 



There are several beautiful species of the Avicula from 

 the Indian Ocean, coast of Brazil, New Holland, the Red 

 Sea, and from the Mediterranean. The valves are shaped 

 like wings ; the interior is pearly in the centre, but some 

 species have a broad black border surrounding it, and the 

 margin is often terminated in a fringe, occasioned either 

 by the epidermis or the foliaceous texture of the exterior. 

 The hinge and other iridescent parts of A. Macroptera 

 are used for making ornaments (bijoux) called peacock's 

 eyes. 



The genus Meleagrina of Lamarck is now classed with 

 Avicula, as the animals resemble each other. 



The A. (Meleagrina) Margaritifera, or Pearl Oyster, is 

 found chiefly in the Persian Gulf, and at Ceylon ; it is lined 

 with a pearly substance, which is 

 formed by the animal in thin 

 layers, and is imported into Eu- 

 rope in large quantities, for the 

 purpose of making knife handles, 

 buttons, &c, under the name of 

 mother-of-pearl. If by any acci- 

 dent the inner surface of the shell 



Avicula margaritifera. 



is injured, so as to cause a frac- 

 ture in the mother-of-pearl, the layers in that place be- 

 come for the future irregular, and a lump is gradually 

 formed, which from accidental circumstances is sometimes 

 oval, sometimes globular, and sometimes pear-shaped. 

 Pearls, as these lumps are called, are occasionally found 

 loose in the shell, and in this case the pearly substance 

 has been deposited upon a loose grain of sand, or diseased 

 ovum or egg of the animal. 



" Pearls are small nacrous balls, that become formed 

 and hardened within the body of the animal; they are 

 found deposited in the most fleshy parts, particularly 



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