96 
NATURAL HISTORY. 
[long 
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, 
for no very honest purpose, 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 (see Case 83). In other countries, spurious Pearls 
have been produced, for an equally laudable object, by 
placing pointed pieces of wire in a similar situation. 
Case 88 contains the shells of Branchiopodous Mollusca, 
which are inclosed by two regular shelly valves. They 
have no distinct head, but the mouth is placed on the 
hinder part of the cavity, and is furnished with two long 
spirally twisted arms, by which they reach their food; 
the organs of respiration are placed on the edge of the 
mantle. All these shells are attached to marine bodies: 
some of them are regular, and somewhat like a Grecian 
lamp in form, and have therefore been called Lamp-shells. 
They are attached by means of a tendinous band, which 
passes out of the hole in the apex of the upper valve, as in 
the Terebratulce and Spiriferi: others, as in the Lingula , 
are attached by a tendinous tube, resembling the stem of 
the Barnacles, which passes out between the apex of the 
valves, which gape in front. The Discince , on the other 
hand, have the tendon passing out of a linear slit near the 
middle of the under valve; and the Cra?iice are imme¬ 
diately attached by the outer surface of their shells. 
LONG GALLERY. 
The Long Gallery above the Kings Library is appro¬ 
priated to the collections of Mineralogy and Secondary Fos¬ 
sils, the arrangement of the latter of which is not yet com¬ 
pleted. The system adopted for the arrangement of the 
minerals, with occasional slight deviation, is that of Pro¬ 
fessor Berzelius, founded upon the electro-chemical theory 
and the doctrine of definite proportions, as developed by 
him in a memoir read before the Royal Academy of Sciences 
