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 Linnaean 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 History. 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, 



