161 
N. ZOOL. GAL.] NATURAL HISTORY. 
the glassy coat on the upper part of the whorls, or the 
deposition of cross septa separating the upper part of the 
cavity from the rest of the shell, which is most perfectly 
developed in the Chambered shell, or Nautili . 
4. Specimen shewing the manner in which the animals 
mend any accident to their shell. 
5. Specimen exhibiting the manner in which Mollusca 
remove by absorption certain parts of the shell which are 
no longer necessary to them, or may be in the way of their 
growth, and of the holes which they make in shells, rocks, 
or wood, to form habitations for themselves and to procure 
their food. 
6. The specimens exhibiting the manner in which the 
tubular shells are rolled up into a spire, beginning with 
the nearly straight Dentalium , gradually passing by the 
irregularly twisted Vermetus and the separate whorled 
Scalaria , to the common spiral shell; others shewing the 
gradations of form in the involute and spiral shell; and 
lastly, some deformed specimens exhibiting the same varia¬ 
tions in different individuals of the same species of Mol¬ 
lusca, and the monstrosities which occur in the form of shells. 
7. Specimens shewing the manner in which Mollusca 
cover with a shelly coat any extraneous body which may 
become attached to its shell. 
In Cases 5 and 6 are a series of plaster casts of the in¬ 
terior of the different shells of living Mollusca to facilitate 
the determination of the cast of the fossil species, which 
are so commonly found in the Portland stone and other 
geological formations; at the same time these moulds are 
useful as shewing the form of the mantle of the dif¬ 
ferent species of Mollusca, which is so liable to be distorted 
or contracted in the preserved specimens, and exhibiting 
how completely the shell is moulded on the body. 
In Cases 7 and 8 are placed a series of models on an 
enlarged scale, and some specimens of minute bodies. 
The nature of the animals which form them is not known; 
and they may belong to several different orders. Some 
have supposed them to be internal shells ; but this cannot 
be the case with all, as many are attached by their outer 
surface to sea-weeds and shells. From their being formed 
of numerous chambers, they have been generally asso¬ 
ciated with the Nautili , but they differ essentially from the 
