BIVALVE MOLLUSCA, 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 J<éleagrina margaritifera, a bivalve, sometimes 
Fig. 162,—Malleus alba (Lamarck). 
designated the intadine, 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. 
