ON MOLLUSCA. ATi ¢ 
phraseology. ‘Those technical terms we are about briefly to 
explain, and we shall conclude by a sketch of the history of 
this science. 
We have, in reality, no other generic terms to indicate the 
hard, calcareous, fragile bodies which form the object of this 
part of natural history, than that of envelope, or better, per- 
haps, of protecting body or of testa; for by that of shells, or 
conche, we simply understand those of the molluscous ani- 
mals. The Greeks had the word ostraca, whence ostraco- 
dermata and ostracea ; and the Latins that of testa, whence 
the denomination testacea, or animals covered with a testa or 
hard envelope. Nevertheless the vulgar appellation of shells 
(more vague perhaps in English than in some other lan- 
guages) has prevailed, and the term conchology is in general 
use. 
Quitting, however, these verbal criticisms, we understand 
by shells or protecting bodies, bodies of a very variable form, 
cretaceous, more or less thin, breaking off readily and com- 
pletely, easy of preservation, and constantly in relation with 
the skin of an animal. 
In considering at first these bodies in a general manner, 
and under the relation of structure, we find a first division of 
shells, namely, into false and true. 
A false shell is that which does not belong to a molluscous 
animal, or rather that which is composed of a great number 
of small polygons applied side by side, and the ensemble of 
which forms a calcareous, hard, and frangible envelope, which 
is seen in the testa of the echinites. 
A true shell is that which is formed of lamine applied one 
within the other; the most recent and the largest being the 
most internal, and the most ancient and smallest the most ex- 
ternal, whatever its form may be and the number of pieces of 
which it is composed. 
