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 conspicuous 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 obstinately 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 bivalves. 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 introduce 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 Strombus 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 quantity, the brilliant nacreous matter. This, investing
