164 
LECTURE XI. 
tilus, and which is the Argonauta vitreus of Lin^ 
naeus, (so very rare that hardly more than four or 
five specimens are to be found in the European 
cabinets) is suspected by an ingenious French Na- 
turalist to be rather the internal shelly support or 
bone of some kind of unknown Molluscous animal, 
than a real and proper shell. Yet, on the other 
hand, we are assured that Monsieur Bonnet has 
actually seen the shell sailing like other species 
of this genus, to which its inhabiting animal is 
greatly allied. 
I shall now proceed to the next Linmean set 
or genus of shells, which is almost equally extra- 
ordinary with that of Argonauta^ and has been 
often confounded with it by careless readers of 
works on Natural Historj''. This is owing to an 
unfortunate similarity of names ; for both have 
been called by the general title of Nautilus. Lin- 
naeus, in order to prevent confusion, named the 
former genus Argonauta^ and restricted the gene- 
ric name Nautilus to that which we are now go- 
ing to consider, and which is in common language 
called the Pearly Nautilus, in order to distinguish 
it from the Paper Nautilus or Argonauta. The 
principal species of the Linnaean genus Nautilus 
is the N. Pompilius, a large and strong shell. 
