﻿UNIVALVES. 



The almost imperceptible gradation in this beautiful class of animals ren- 

 ders the present mode of classification peculiarly interesting, as we are not 

 under the necessity of separating nearly allied families, as in the classing of 

 most other natural productions. Most of the shells of this division possess a 

 regular spiral curve very conspicuous in many of the genera, but gradually be- 

 coming obsolete. 



Learn of the little Nautilus to sail; 



Spread the light oar, and catch the passing gale. 



No. 18. ARGONAUTA. 



Proper Nautilus. Inhabitant a Sepia or Clio. 



All the Argonauta are marine shells of exceeding brittle texture, and possess 

 great elegance of form. The ancients are said to have derived their art of nav- 

 igation from the animals inhabiting these shells, which raise themselves 

 to the surface by ejecting the sea-water from their shells, and, on the ap- 

 proach of danger, draw in their arms, and with them a quantity of water, 

 which occasions them to sink immediately. By possessing this power, they 

 are but rarely taken perfect, as the instant they are disturbed they disappear, 

 and are only accidentally brought up, in the nets of fishermen, or found 

 left dry on rocks. 



