CLASS CEPHALOPODA. 13. 
NAUTILUS, properly so called, 
Has a shell which differs from the spirula in the sudden 
crossing of the lamin, and in the last turns of the spire, which 
not only touch the preceding ones but envelope them. The 
siphon occupies the centre of each septum. 
N. pompilius, L.; List. 551, the most common species ; it 
is very large, formed internally of a beautiful mother-of-pearl, 
and covered externally with a white crust, varied with fawn- 
coloured streaks or bands. 
The animal, according to Rumph, is partly contained within 
the last cell, has the sac, eyes, parrot beak, and funnel of the 
other cephalopoda; but its mouth, instead of having their 
large feet and arms, is surrounded by several circles of nume- 
rous small tentacula without cups. A ligament arising from 
the back traverses the whole siphon and fastens it there. It 
is probable that the epidermis is extended over the outside of 
the shell, though we may presume it is very thin over the parts 
that are coloured. 
Individuals are sometimes found, Naut. pompilius, 3, 
Gmel.; List. 552; AMMONIE, Montf. 74.; in which the last 
whorl does not envelope and conceal the others, but where all 
of them, though in contact, are exposed, a circumstance which 
approximates them to the ammonites; they so closely resem- 
ble the common species, however, in all the rest of the shell, 
that it is scarcely possible to believe them to be any thing 
more than a variety of it. 
Fossil nautili are found of a large or moderate size, and 
much more various, as to form, than those now taken in the 
ocean. 
Chambered shells are also found among fossils, furnished 
with simple septa and a siphon, the body of which, at first 
arched, or even spirally convoluted, remains straight in the 
more recent parts; they are the Liruus of Breyn, in which 
