68 UNIVALVES. ARGONAUTA. 



ORDER III. 



^nit^Siit^t^, 



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



ARGONAUTA— Paper Sailor. 



Animal — a Clio: Shell univalve, spiral, involute, ment' 

 branaceous, one celled, 



THE genus Argonauta contains but five 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, 

 proceeding from the summit to the outer margin, which 

 is generally bicarinated ; but in the A. vitrea (the glassy 

 nautilus) the margin is single : this is the most rare and 

 beautiful species of the genus.* 



* There are only three shells of this species known ; one in the 

 possession of the Earl of Mountnorris, another in the Public Col- 

 lection at Paris, and a third in the cabinet of a French gentleman. 



