103 
another contrivance is adopted, apparently for the production of this 
effect — the rendering the weight of the mass so near to that of water, 
that a very slight change may occasion or destroy its buoyancy. 
Should the opinions here offered be found to be objectionable, it may 
be considered, in excuse, that the economy of the animal has hitherto 
undergone but little investigation. So little, indeed, has the structure 
and the nature of the siphunculus been understood, that even De Bose, 
the latest writer, perhaps, on the subject, points out no other use of 
this tube to the animal, than that of its serving to conduct its tail to the 
beginning of the spire. “ II n’y a pas de doute que ce tuyau ne serve 
a conduire la queue de l’animal a l’origine de la spire oil elle s’attache.” 
Histoire naturelle des coquilles, Tome V. p. 164. 
We at present know, in a recent state, and of a size sufficiently large 
to allow of an examination of the structure, without the aid of a micro- 
scope, but one species of nautilus, N. pompilius. There is, however, 
no doubt of several distinct species existing in a mineralized state. 
In Shepey Island, in the corresponding stratum of Brentford, in 
some parts of Somersetshire, particularly near Bath, and, I doubt not, 
but in several other parts of this island, a fossil nautilus is found, which, 
from the roundness of the back part of the shell, may be concluded to 
approach exceedingly near, at least in its form, to N. pompilius. Some 
of these, which have been found at Shepey, where they are mostly 
imbedded in septaria, as well as those which have been found at 
Brentford, are of very considerable magnitude, and seem to resemble 
N. pompilius in their internal structure. 
The outside of these fossils are frequently resplendent, with a pearly 
coat. This circumstance demands some little consideration ; since, as 
this is not the case with the outside of the shell of N. pompilius, it seems 
to point out the fossil as a different species, as the nacre does not exist 
on the outside of the shell of the recent species. Future observations 
will determine this question more decidedly ; but at present, I am 
disposed to imagine, that, in the fossil specimens, the external part 
