374 
Dyes. 
MOLLUSCA. 
Mollusca. ropean seas, that the pearls of commerce are procured. The 
—Y— Pinna, so famous for furnishing a byssus or kind of thread, 
with which garments can be manufactured, likewise pro- 
duces pearls of considerable size. They have seldom the 
silvery whiteness of the pearls from the Avicula, being usually 
tinged with brown. But the shell which in Britain produces 
the finest pearls, is the Alasmodon margaritiferum, which was 
placed by Linneeus in the genus Mya. It is found in all 
our alpine rivers. The Conway and the Irt in England, the 
rivers of Tyrone and Donegal in Ireland, and the Tay and 
the Yythan in Scotland, have long been famous for the pro- 
duction of pearls. These concretions are found between 
the membranes of the cloak of the animal, as in the Avi- 
cula, or adhering to the inside of the shell, as in the Unio. 
In the former case, they seem to be a morbid secretion of 
testaceous matter; in the latter, the matter seems to be ac- 
cumulated against the internal opening of some hole with 
which the shell has been pierced by some of its foes. Lin- 
nus, from the consideration of this circumstance, endea- 
voured, by piercing the shell, to excite the animal to se- 
crete pearl; but his attempts, though they procured him a 
place among the Swedish nobility and a pecuniary reward, 
were finally abandoned; the process being found too tedi- 
ous and uncertain to be of any public utility. The largest 
pearl of which we have any notice, is one which came from 
Panama, and was presented to Philip I. king of Spain, in 
1579. It was of the size of a pigeon’s egg. Sir Robert 
Sibbald mentions his having seen pearls from the rivers of 
Scotland as large as a bean. 
Besides yielding us a variety of wholesome food, and valu- 
able ornaments, testaceous animals supply us with a beauti- 
ful dye. The Purpura of the ancients, according to the 
opinion of Rondeletius, confirmed by the observations of 
Cuvier, was chiefly extracted from the shell termed Murex 
brandaris. Since the introduction of the cochineal insect, 
the use of this dye has been superseded, so that we are now 
in a great measure ignorant of the process which the an- 
cients employed to extract it. In Britain there are several 
kinds of shell-fish, which furnish a dye of this sort, but these 
are seldom sought after. Cole, in 1685, published a method 
of obtaining it from the Purpura lapillus, to which Mon- 
tagu, in the supplement to Zestacea Brittanica, has added 
several important directions. When the shell is broken in 
a vice, there is seen on the back of the animal, under the 
skin, a slender longitudinal whitish vein, containing a yel- 
lowish liquor. When this juice is applied to linen, by means 
of a small brush, and exposed to the sun, it becomes green, 
blue, and purple, and at last settles in a fine unchangeable 
crimson. Neither acids nor alkalies affect its colour, and it 
may be conveniently employed in marking linen, where an 
indelible ink is desirable. The Scalaria clathrus (Turbo 
clathrus of Linnzeus) also furnishes a purple liquor of con- 
siderable beauty, but it is destructible by acids, and gradu- 
ally vanishes by the action of light. The Planorbis cor- 
neus likewise yields a scarlet dye, but of still less perman- 
ency than the scalaria, as all attempts to fix it have hitherto 
proved ineffectual. 
We cannot conclude this chapter without remarking, that 
the study of molluscous animals rises in importance as we 
perceive its utility. When we are told, that searching for 
shell-fish, and conveying them to the market, give employ- 
ment to a British population of upwards of 10,000; that 
these animals furnish nourishing food to innumerable fami- 
lies, and in years of scarcity prevent the horrors of famine ; 
we will be disposed to regard with a favourable eye the la- 
bours of that naturalist who examines the structure and 
economy of those animals, that, from a knowledge of their 
nature, he may render them still more subservient to our 
Shells as purposes. 
objects of 
amusement cous animals are not devoid of interest. 
Even when considered as objects of amusement, mollus- 
In the preceding 
division of our subject, we have considered them as appli- Mollusca. 
cable to various useful purposes, and expressed our regret, ——\—= 
at the same time, that no one qualified for the task had ever 
bestowed on economical conchology an attentive examin- 
ation. We cannot therefore consider the present condition 
of the science as the result of the labours of its practical 
admirers. The lovers of this study, as an agreeable amuse- 
ment, have at all times been numerous, from the days of 
Lzlius and Scipio to the present time; and it is to their 
exertions as collectors, that the science is principally in- 
debted for its present state of improvement. The colours 
of shells are often so intensely vivid, so finely disposed, and 
so fancifully variegated, that, as objects of beauty they rival 
many of the esteemed productions of the vegetable king- 
dom. In their forms they likewise exhibit an infinite va- 
riety. While some consist merely of a hollow cup or a sim- 
ple tube, others exhibit the most graceful convolutions, and 
appear in the form of cones, and spires, and turbans; and 
in another division, shaped like a box, all the varieties of 
hinge are exhibited, from that of simple connexion by a 
ligament to the most complicated articulation. The forms 
of shells are indeed so various, and many of them so ele- 
gant, that a celebrated French conchologist warmly recom- 
mends them to the attentive study of the architect. ‘ Or,” 
says Lamark, “comme l’extréme diversité des parties pro- 
tubérantes de la surface de ces coquilles, ainsi que la régu- 
larité et l’élégance de leur distribution, ne laisse presque 
aucune forme possible dont la nature n’offre ici des exam- 
ples; on peut dire que architecture trouvéroit dans les 
espéces de ce genre (Cerithium) de méme que dans celles 
des pleurotomes et des fuseaux, un choix de modéles pour 
Yornement des colonnes, et que ces modéles seroient trés 
dignes d’étre employés.” (Annales du Mus. vol. iii. p. 269.) 
In this country, however, no such recommendation is ne- 
cessary, as many of our beautiful ornaments of stucco, par- 
ticularly for chimney-pieces, are copied from the univalve 
testacea, and are greatly admired. 
But shells, even with all their beauty and elegance, would 
never have acquired so much importance in the eyes of 
amateurs, had their forms been as difficult to preserve as 
the external coverings of the higher classes of animals. It 
is both a tedious and a difficult operation to preserve a quad- 
ruped, a bird, or a fish, as a specimen for the cabinet, and 
even when the task is completed, it is but of temporary dur- 
ation. A slow but certain process of dissolution is going on, 
which, though invisible for a time to the owner, gradually 
destroys the finest collection of these objects. The very 
changes of the atmosphere, combined with the attacks of 
insects, accelerate the destructive process. But with shells 
the case is very different. Composed of particles already 
in natural combination, they do not contain within them- 
selves the seeds of dissolution, so that for ages they remain 
the same. Besides, all that is in general necessary to pre- 
pare a shell for the cabinet, is merely to remove the ani- 
mal. When the sheli is covered with foreign matter, we 
must wash it away with a brush in soap in water ; and it is 
frequently necessary to steep the shell for some time in fresh 
water, to extract all the salt water which may adhere to it. 
After being properly dried it is fit for the shelf of the cabi- 
net, and stands in no need of anxious superintendence. 
Amateurs are seldom contented with the simplicity of na- Polishing 
Vitiated in their taste by a fashion which abides by of Shells. 
ture. 
no rules, they-attempt to improve even her most elegant 
productions, and delight to exhibit in their cabinets some 
of the efforts of their art. As such are in search of inno- 
cent amusement, we mean not to dispute about the propriety 
of their conduct, but rather shortly to mention, for their edi- 
fication, the method generally in use to improve the beauty 
of testaceous objects. Many shells, it is true, naturally pos- 
sess so fine a polish, that no preparation is considered as ne- 
cessary before placing them in the cabinet. Such are the 
