ARTIFICIAL PEARLS. 91 



large and handsome. The large lappets on each side 

 of the neck, and the wing- like appendages of the 

 mantle, furnished with tentacular filaments, are con- 

 spicuous when it crawls; though these parts are less 

 vividly coloured than in its more common congener. 

 Neither species unfortunately thrives, according to 

 my experience, in an Aquarium ; they sometimes ob- 

 stinately refuse to protrude from the very first, and, 

 after lingering a few days, die where they were put in. 

 The chief glory of this genus is the richly pearled 

 internal surface of their shells, in which they are not 

 excelled by any, even of the true margaritiferous bi- 

 valves. Both of the species I have named are very 

 brilliant, and it might be worth while to experiment 

 on them in the manner in which it is reported that 

 pearls are artificially produced by those ingenious 

 rogues the Chinese. Dr. Gray says that they intro- 

 duce little pieces of silver wire, bent into a peculiar 

 form, between the mantle of the pearl-oyster, while 

 yet alive, and the shell ; not perforating the shell, as 

 has been sometimes stated. This zoologist himself 

 tried the experiment on the Unio, a bivalve of our 

 fresh waters, and was very sanguine as to its success; — 

 but I have never heard of any one having suggested 

 the formation of pearls by the Trochi, though as these 

 beautiful objects are produced spontaneously by some 

 univalves, (as Stromhus for example), I do not see 

 why it may not be possible. The origin of loose 

 pearls is known to be the irritation caused by some 

 extraneous body, to get rid of which the secreting 

 surface of. the animal throws off in unusual quan- 

 tity, the brilliant nacreous matter This, investing 



