314 EXTENT OF THE GENUS NAUTILUS. 
I must enter at some length into the natural 
history of these shells, because the conclusions 
to which I have been led, by a long and careful 
investigation of fossil species, are at variance 
M ith those of Cuvier and Lamarck, as to the fact 
of Ammonites being external shells, and also 
with the prevailing opinions as to the action of 
the siphon and air chambers, both in Ammo- 
nites and Nautili. 
3IecJia7iical Contrivances in the Nautilus. 
The Nautilus not only exists at present in our 
tropical seas, but is one of those genera which 
occur in a fossil state in formations of every 
age ; and the molluscous inhabitants of these 
shells, having been among the earliest occu- 
pants of the ancient deep, have maintained 
their place through all the changes that the 
tenants of the ocean have undergone. 
The recent publication of Mr. R. Owen's ex- 
cellent Memoir on the Pearly Nautilus, (Nautilus 
Pompilius Lin.) 1832, affords the first scientific 
description ever given of the animal by which 
this long-known shell is constructed.* This 
* 
It is a curious fact, that although the shells of the Nautilus 
have been familiar to naturalists, from the days of Aristotle, and 
abound in every collection, the only authentic account of the 
animals inhabiting them, is that by Rumphius, in his history of 
Amboyna, accompanied by an engraving, which, though tole- 
