75 
UNIVALVES. 
ARGONAUT A. 
(Plate XII. Fig. 1.) 
Shell univalve, spiral, involute, membranaceous, 
unilocular or without chambers. Aperture cor- 
date. 
This delicate and brittle shell, composed as it 
were of two parts, of the two sides connected by 
the keel, approximates more nearly to the bivalves 
than any other univalve, and is therefore placed 
foremost in the last division of Testacea. 
The Nautilus of Pliny has been separated from 
the chambered genus, bearing that name in the 
Linnsean System, and has been denominated Ar~ 
gonauta, from ’A^yomurT^g, a companion of Jason 
in the celebrated voyage of the ship Argo. The 
art of navigation is supposed to have owed its origin 
to the expert management of this instinctive sailor. 
He was observed by the ancients, and subsequent 
experience has confirmed the observation, to raise 
