526 AVICULIDiE. 



tada, Bolt. Perlamater, Schum. Meleagrina, Lam. Mar- 

 garita, Leach. 



Ex. M. margaritifera, Linnmis, pi. 122, fig. 6, G, a. 



The principal difference between the " Pearl Oysters " 

 and the Avicuhp, consists in the more orbicular form and 

 the equality of the valves. The inner layer of the shells is 

 employed in the manufacture of various objects and for the 

 purpose of inlaying under the name of " mother-o'-pearl." 

 The pearls of commerce, which are detached portions of 

 the nacre of the interior, are also obtained from various 

 species of this genus. The pearl fisheries of Ceylon and 

 the Persian Gulf ai*e the most famous. The shells are 

 procured from about twelve fathoms water. 



Species of Margariiifera. 



albina, Lam. lurida, Gould. 



aluco, Phil. maculata, Gould. 



Chemnitzii, Phil. margaritifera, Linn. 



fimbriata, Dkr. Mazatlanica, Hani. 



foliacea, Bolt. nigra, Gould. 



fucata, Gould. psittacea, Phil. 



glabra, Gould. radiata, Leach. 



imbricata, Bolt. semiaurata, Linn. 



inflata, Schum. strix, Phil. 



laticauda, Phil. vidua, Gould. 



Genus isognomon, Klein. 



Shell nearly equivalve, compressed; surface of valves 

 lamellar; right valve with a byssal sinus. Hinge linear, the 

 area wide, with numerous transverse, elongated cartilage- 

 pits. Muscular impression large, sub-central, double. 



Syn. Melina, Retzius. Pedalion, Solander. Sutura, 



