(ae) 
C. Shells exterior ; not chambered. 
6. Arconaura. (1) 
Ditto. Two of the tentacula 
with a membranous en- - 
largement. 
(4) The animal uses its shell as a boat, and when the sea is calm it is seen navi- 
gating on the surface, employing six of its tentacula as oars, and raising two, which, 
from the considerable membranous enlargement, serve as sails. Pl. 15, fig. 1. If 
the waves are agitated, or any danger appears, the Argonaut draws its tentacula or 
arms within the shell, concentrates itself, and sinks to the bottom. The ancients 
were acquainted with this singular animal and its manceuvre; it is their Nautilus 
and Pompilus.—Plin. IX, cap. 29. Blainville and Dr. Leach consider the animal 
found in the 4. argo (PI. 15, fig. 2) to be parasitical, and allied to the Octopus, 
under the name of Ocythoé. 
