624 
MOLLUSCA. 
THE COMMON MUSSEL. 
having heard of Howell's good and bad fortune, became a pearl-hunter, and, after wading about 
in the mud of Notch Brook for many days, found a mussel from which he extracted a splendid 
pearl, five-eighths of an inch in diameter. It was of perfect form and pure colors, and was sold 
to Messrs, Tiffany & Co., of New York, for a thousand dollars. This was sent to Paris, and re- 
sold for twenty-tw^o hundred dollars. These incidents produced a general pearl-hunt all over the 
country, and a number of small pearls were found ; but the search was, on the whole, unsuccess- 
ful, and it is now abandoned. 
THE MYTILACEA. 
This includes several genera of what are properly called Mussels ; these live mostly, if not 
entirely, in salt water; the fish has a byssus by 
which the animal usually attaches itself to some rock 
on the shore. The valves are generally equal, of an 
elongated form, and pearly inside. Many of the 
species conceal themselves by burrowing into various 
substances; some can penetrate rocks, corals, and 
shells for this purpose. Some species make use of 
the byssus to spin themselves a sort of net. Though 
inferior to the oyster, immense quantities of the 
Common Mussel, Mytilus edulis, are eaten in Eu- 
rope : four hundred thousand arc said to be annually 
consumed in Edinburgh and Leith, and thirty or 
forty millions to be used for bait in the Frith of 
Forth. Several species of this genus occur on our 
American coasts. 
THE ARCACEA. 
In these the shells are nearly equal, usually thick and furnished with a long row of teeth at the 
hinge. Among them is the Area tortuosa, 
the shell somewhat twisted and striated ; 
found in the Indian Ocean. The A. jiexata^ 
common on our coasts, is called the Bloody 
Clam, because, on being opened, there issues 
from it a flow of reddish liquid. There are 
other American species. The A. transversa 
is common from Cape Cod to the coasts of 
THE AECA TORTuosA. ^cw Jcrsey. 
THE AVICULACEA. 
In this tribe, which is rendered important by its including the Pearl-Oyster, the foot is 
small, and produces a byssus by which the animal attaches itself firmly to submarine objects. 
The mantle lobes are free ; the shell usually oblique and somewhat triangular, with the valves 
unequal, and the hinges without teeth. 
Most of the shells are pearly in the interior ; and as the true pearls are merely morbid growths, 
they may all produce pearls of various qualities. The formation of pearls is caused by the intro- 
duction of irritating substances, such as grains of sand, between the mantle and the shell. The 
irritation causes the animal to cover the obnoxious object with layers of pearl, which generally 
attach the foreign body to the interior of the shell. The Chinese produce pearls artificially by 
placing substances in the position thus described. 
The Pearl-Oyster, Meleagrina margaritifera, furnishes the finest pearls; the shells are also 
imported in vast quantities, the inner layer, known as " mother of pearl," being used for a great 
number of ornamental purposes. This species is found in various parts of the Indian and Pacific 
Oceans, at a depth of about twelve fathoms, where they are taken by divers. A considerable 
number of pearls are procured on the coasts of Panama, but many of them are of irregular form. 
