BIVALVE MOLLUSC A. 



363 



of the shell, its mantle fringed by very small tentacular appendages. 

 Only six actually living species of the genera are known, which are 

 inhabitants of the Indian Ocean, of the Australian seas, and the 

 Pacific Ocean. 



The beautiful diaphanous nacre which embellishes the interior of 

 so many ornamental cabinets is principally produced by the animal 

 inhabiting the Meleagrina ftiargaritifera, a bivalve, sometimes 



Fig. 162.— Malleus alba (Laaoaxok). 



designated the Phitadine, or mother-of-pearl shell. This bivalve 

 moors itself to the bottom of the sea by a strong byssus of a 

 brownish colour. The valves of the shells are irregularly rounded 

 in their young days ; they are externally lightly foliated, and orna- 

 mented with bands of green and white, which spring from the summit 

 in rays, and afterwards break off into two or three slightly scattered 

 branches. In old age they become rugged and blackish. The shell 

 is in its perfection when about eight or ten years old, their size being 

 then about six inches in diameter, with a thickness of about an inch 

 and a quarter. 



