75 



UNIVALVES. 



ARGONAUT A. 

 (Plate XII. Fig. I.) 



Shell univalve, spiral, involute, membranaceous, 

 unilocular or without chambers. Aperture cor- 

 date. 



Tliis 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 

 Ibremost in the last division of Testacea. 



The Nautilus of Pliny has been separated from 

 the chambered genus, bearing that name in the 

 Linnaean System, and has been denominated Ar- 

 gonauta, from 'A^yomurrjg, 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 



