the name of a genus of shell fish belonging to the order of vermes testacea. The shell consists of one spiral involuted valve. There are two species of Argonauta, viz. The argo, with a subfunded carina, which is found in the Mediterranean and Indian oceans. This is the famous nautilus of authors. The shell seems no thicker nor stronger than a piece of paper; and the fish that inhabits it is a sepia. It has been imagined that men first learned the method of failing in vessels from what they saw practised by this creature. When it is to fail it extends two of its arms on high; and between these supports a membrane, which it throws out on this occasion: this serves for its sail; and the two other arms it hangs out of the shell, to serve occasionally either as oars or as a steerage; but this last office is generally served by the tail. When the sea is calm, it is common to see numbers of these creatures diverting themselves with failing about in this manner; but as soon as a storm rises, or anything gives them disturbance, they draw in their legs, and take in as much water as makes them somewhat heavier than the sea-water in which they swim, and they then sink to the bottom. The manner of their voiding this abundant water, when they would rise again, is by a number of holes, of which their legs are full. 2. The cymbium, with a blunt plaited carina. This species is very small, and is found in the Mediterranean.