87 



UNIVALVES, 



ARGONAUTA. 

 (Plate XII. % 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 connect- 

 ed 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 Lin- 

 naean System, and has been denominated Argo- 

 nauta, from '^gyovauT*;;, 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 



