UNIVALVES. ARGONAUTA. 77 



its arms erect, and a membrane thrown out between them, 

 by which means it is driven forward, like a vessel under 

 sail. The Mediterranean often has large fleets of these 

 diminutive navigators floating upon its calm surface. 



The colour of the Argonautae is mostly blueish, or yellow- 

 ish-white, having the keel often tinged with a brownish 

 hue. 



As to size, the Argonautse differ greatly; the A. argo, 

 for instance, often attains ten or twelve inches in width ; 

 while the A. cornu and A. arctica seldom exceed three or 

 four lines in diameter. 



The Mediterranean and Indian seas produce some va- 

 rieties ; others are found at the Cape of Good Hope ; and 

 some inhabit the Northern and Greenland seas. 



They are supposed to have derived their name from the 

 Argonauts. 



ARGONAUTA Paper Sailor. 



DIVISION I. KEEL TOOTHED. 

 FAMILY 1. Summit interiorly curved. 

 Argo Oriental. Hians Gaping. 



Tuberculata Tuberculated. Gondola Boat. 

 Haustrum Bucket. 



FAMILY 2. Summit exteriorly curved. 

 Vitrea Brittle. 



DIVISION II. KEEL NOT TOOTHED. 

 Cyinbium Minute. Cornu Horn-shap'd. 



DIVISION III. UMBILICUS PERFORATED. 

 Arctica Arctic. 



