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 Ai-gonautee is mostly blueish, or yellow- 

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

 hue. 



As to size, the Argonautae 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— Pa/)cr 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. 

 Cymbuim — Minute. Cornu — Horn-skap'd. 



Division III. — Umbilicus perforated. 

 Arctica — Arctic. 



