THE PEAKL OYSTER. 353 



very strong ligament which acts upon the valves. The animal is 

 contained in the interior of the shell, its mantle fringed hy 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 are principally produced by the animal 

 inhabiting the Meleagrina, a bivalve, sometimes designated the pinta- 

 dine, or mother-of-pearl shell. This bivalve moors itself to the bottom 

 of the sea by a strong byssus of a brownish colour. The door-posts 

 of the shells are irregularly rounded in their young days ; they are 

 externally lightly foliated, and ornamented 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. 



Nacre is the hard and brilliant substance with which the valves of 

 certain shells are lined in the interior. This substance is white, 

 silky, slightly azure, and more or less iridescent. Most of the bivalves 

 are supplied with nacre ; some of them even yield a blue, or blue 

 and violet pigment. The iridescent Haliotis iris, for instance, is an 

 emerald-greenish blue of changing colour, with reflections of a purple 

 violet. Turbo argyrostomus (Linnaeus) presents a mouth of bright 

 silvery hue, while Turbo chrysostomus appears in all the glory of 

 gold ; but the Pintadine yields the purest white nacre, as well as the 

 most uniform, and especially the thickest. This product owes its 

 brilliant and delicate appearance to the play of light on it in its 

 highly-polished state. For practical purposes the nacre is separated 

 from the shell with an instrument ; sometimes all the exterior part of 

 the shell being dissolved away from the precious substance, leaving 

 only the naked bed of nacre. 



But the most interesting of all the nacre-bearing shells is the pearl 

 oyster (Meleagrina margaritifera], the exterior, as well as the interior, 

 of which is represented in Fig. 164. The interior of the shell affords 

 the most exquisite pearls ; the Esterhazy collection of jewels afforded 

 many such specimens. This shell is nearly round, and greenish in 

 colour on the outside ; it furnishes at once the finest pearls, under 



2 A 



