CONCHOLOGY. 
Shells appear to form a part of the cre- 
ation not immediately subsendent to the 
purposes of human life. This being admitted, 
still tliey are a link in the great chain of 
nature ; they constitute a department of ra- 
tional inquiry worthy the researches of the 
man of science ; and when we consider the 
amazing diversity of singular and beautiful 
objects they embrace, are such, we are 
persuaded, as cannot foil to arrest, in a 
particular degree, the regard of every com- 
mon observer. 
The term conchology comprehends the 
study of all animals which have a testaceous 
covering, whether inhabitants of the ma- 
rine element, fresh water, or the land. Tes- 
taceology is a terra sjnionymous with con- 
chology, but is of later origin and applica- 
tion. 
A precise distinction should be drawn be- 
tween testaceous and cmstaceous animals ; 
they are essentially different ; though both 
are protected by a hard exterior shell or 
crust, in which they are partially or en- 
tirely enveloped ; and have been indiscri- 
minately confounded together, for that rea- 
son, under the vague denomination of shell 
fish. Some of the old writers distinguish 
the testacea as a kind of stone-like calca- 
reous covering or habitation, in which the 
animal, otherwise naked, resides, and from 
which it can protrude its molluscous arms, 
or other naked parts of its body, at plea- 
sure. The ctustaceous animals of those au- 
thors, on the contrary, are not naked, but 
have every particular limb or part sepa- 
rately covered With the crust, w'hich is thus 
divided into many joints, insomndi that the 
whole animal assumes a loricated appear- 
ance, as if inclosed in a coat of mail. 
Among the crustaceous order, the cimeri, or 
crabs and lobsters, were included. A bet- 
ter definition may be obtained by attending 
to the chemical properties of the two sub- 
stances testaceous and crustaceous. Poli, 
in his work on the shells of the two Sicilies, 
demonstrates that testaceous bodies consist 
of calcareous earth united to a small por- 
tion of animal matter or gluten ; and Mr. 
Hatchett, whose experiments on the che- 
mical characters of those bodies are in- 
serted in the Transactions of the Royal So- 
ciety, draws a striking distinction from ana- 
lysis between the testaceous and crusta- 
ceous bodies, ascertaining the first to con- 
sist only of carbonate of lime mixed with 
gelatinous matter, while in the other the 
presence of phosphate of lime was detected. 
The crustaceous body analysed by Mr. 
Hatchett svas the echinus. 
AH testaceous animals are composed ot 
two parts ; one of which, the animal itself, 
is soft and molluscous ; the other, is the 
shell, or habitation, which is hard, of a 
stony or calcareous nature, and either par- 
tially or entirely covers the animal. The 
animal is attached to the shell by means of 
ligaments or muscles. 
It was long considered as a matter of 
dispute among naturalists, whether the ar- 
rangement of sliells should be constituted 
from the animals or their habitation. No 
one can deny, that if we proceed on prin- 
ciples strictly scientific, we must regard 
them as a department of zoology, and 
should, on that account, dispose them ac- 
cording to the nature and structure of the 
animals. But tlie classification formed from 
the characters of the shells is universally 
followed, and we nnist confes'-', too, is for 
many reasons preferable to any other. Nei- 
ther is it, in the hands of the skilful coiu 
chologist, attended with so much indecision 
as might be generally imagined. 
In the first place, among the vast variety 
of shells hitherto discovered, how small, 
comparatively, is the number of those whose 
animal inhabitant is described or known. It 
is not of species only that we speak, but of 
whole natural families or genera, not a sin- 
gle species of which has been yet disco- 
vered with the animal appertaining; so lit- 
tle are we acquainted with the moliiiscous 
orders, or animals inhabiting the shells. Of 
the shells we dally see in collections few are 
fished up alive, the far greater number arc 
found on shores, dead or empty. Neither, 
if it were otherwise, are accurate descrip- 
tions of animals whose parts are not easily 
seen, or anatomical investigations, w'hich 
are in many cases necessary, within the ca- 
pacity of every one. Many of their parts, 
and their respective functions, are not to 
be ascertained, except by comparative 
analogy, and which in itself presents an in- 
surmountable difficulty, or a field of criti- 
cal inquiry so extensive and complicated 
that few, even with the ability to pursue it 
with success, could be prevailed upon to 
devote that attention to the subject which 
it requires. 
Hence it becomes impossible to arrange 
the tar greater miniber of testaceous pro- 
ductions by the animals ; the attempt must 
ever prove unsuccessful. Our arrangements 
would be partial, and three-fourths of the 
