ORDER III. 



UNIVALVES 



I. SHELLS OF ONE PART ONLY, AND HAVING A REGULAR SPIRE. 



ARGONAUTA.— Paper Sailor. 



Animal — a Clio: Shell univalve, spiral, involute, membra- 

 naceous, one celled. 



THE genus Argonauta contains but nine species : in so 

 small a number, much variety is not to be expected. 



The form resembles a scroll, with a large aperture. The 

 surface is ornamented with canaliculated grooves, proceed- 

 ing from the summit to the outer margin, which is gene- 

 rally bicarinated; but in the A. vitrea (the glassy nautilus) 

 the margin is single : this is the most rare and beautiful 

 species of the genus. 



The Argonautae are remarkable for their excessive thin- 

 ness, brittleness, and lightness. The A. argo, usually 

 known by the name of the Paper Nautilus, is supposed, in 

 the early ages of society, to have first taught men the use 

 of sails. 



A mucilaginous animal, called Poulpe, is often mistaken 

 for the Paper Nautilus; it is seen sailing on the ocean with. 



