NATURAL HISTORY, 
74 
[east. zool. 
come, are often to be seen remaining on the outside of the umbones of 
the adult shells. 
The animals of most of the larger species of these shells are used 
for food in various parts of the world. Many of them are liable to a 
disease which causes them to form calcareous pearly secretions, either in 
the substance of their bodies or on the surface of their shells ; these se¬ 
cretions always agree in colour with that of the inner surface of the shell 
to which the animal belongs. Thus those of the Pinnce are pale brown 
and transparent; those of the Oyster are white and opaque ; and those 
of the Muscles are either white or purple; while those of the shells 
which have a pearly lustre, as the Aviculce , Uniones , and Anodons , par¬ 
take of the same mild brilliancy. As the peculiar lustre of Pearls 
greatly depends on their more or less globular form, the Chinese have 
attempted, not very honestly, to make the pearly inside coat of some of 
the pond-muscles assume that shape, by placing hemispherical pieces of 
mother-of-pearl between the animal and the shell, which it eventually 
covers with a pearly coat. In other countries, spurious Pearls have 
been produced, for an equally laudable object, by placing pointed 
pieces of wire in a similar situation. 
These animals are divided into orders, according to their habits, 
which are indicated by some having long syphons, to facilitate the ad¬ 
mission of the aerated water and food, and others only a posterior slit 
between the lobes of the mantle, some having a foot for walking from 
place to place, for attaching themselves to other bodies, and some being 
quite destitute of this organ. 
I. In the more typical orders, the hinder edge of the mantle is fur¬ 
nished within with two (separate or united) syphons, which are provided 
with a large fan-shaped muscle on each side, for the purpose of re¬ 
tracting them into the shell w 7 hen the animal fears external danger. 
The edges of these muscles form, according to their extent, a more or 
less deep sinuosity in the hinder part of the muscular impression, which 
passes round the inner margin of the shell. They are also furnished 
with two distinct adductor muscles, for the purpose of closing the shell 
to protect the animal from injury ; these leave an interior and posterior 
scar on the oblong elongate valves, w r hich are generally provided with 
distinct cardinal teeth under the umbones. 
In the Phyllopoda, so called because the foot is generally lamellar 
or elongate, the gills are not produced into the canal of the syphon ; 
the mantle-lobes are generally separate below, and the syphons are 
elongated, and generally separate from each other at the topi 
The family of Venerid^ have short syphons, which are united for 
the greater part of their length, and they have an external cartilage, 
and three diverging teeth in their hinge, and none, or only rudimentary 
lateral teeth. They live on the sea shore. Some few, as Venerupis , 
form holes in rocks. The Artemis have an orbicular shell, with an angular 
syphonal inflection, and a large lunate inferior foot; the other genera 
have a lanceolate anterior foot; some of these have a small conical an¬ 
terior tooth near the cardinal teeth, as Cyiherea and Meroe , which have 
the hinder lateral tooth striated, and Grateloupea and Trigona have it 
torn and divided ; the Chione and Circe have this tooth smooth; the 
former have a distinct and the latter no syphonal inflection. The Dosime 
