in zoology; a genus belonging to the order of vermes testacea. The shell consists of one spiral valve, divided into several apartments by partitions. There are 17 species, chiefly distinguished by particularities in their shells.

Bonatius observes, that this genus of shell-fish is very well named from the Greek nautilos, which signifies both "a ship" and "a sailor;" for that the shells of all the nautili carry the appearance of a ship with a very high poop. Different authors, both ancient and modern, have called the nautilus by the names of pompilus, nauplius, nauticus, ovum polypi, polypus testaceus; and the French call it le voilier. It is by some imagined, that men first learned the art of navigation from this animal.

The most remarkable division of the nautili is into the thin and thick-shelled kinds. The first is called nautilus papyraceus; and its shell is indeed no thicker than a piece of paper when out of the water. This species is not at all fastened to its shell; but there is an opinion, as old as the days of Pliny, that this creature creeps out of its shell, and goes on shore to feed. When this species is to fail, it expands 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 its 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 frequent to see numbers of these creatures diverting themselves in this manner: but as soon as a storm rises, or any thing gives them disturbance, they draw in their legs, and take in as much water as makes them specifically heavier than that in which they float; and then they sink to the bottom. When they rise again, they void this water by a number of holes, of which their legs are full. The other nautilus, whose shell is thick, never quits that habitation. This shell is divided into 4 or more partitions, which grow smaller and smaller as they approach the extremity or centre of the shell: between every one of these cells and the adjoining ones there is a communication by means of a hole in the centre of every one of the partitions. Through this hole there runs a pipe of the whole length of the shell. It is supposed by many, that by means of this pipe the fish occasionally passes from one cell to another; but this seems by no means probable, as the fish must undoubtedly be crushed to death by passing through it. It is much more likely that the fish always occupies the largest chamber in its shell; that is, that it lives in the cavity between the mouth and the first partition, Navy

Some authors call this shell the *concha margaritifera*; but this can be only on account of the fine colour on its inside, which is more beautiful than any other mother-of-pearl; for it has not been observed that this species of fish ever produced pearls. It must be observed, that the polypus is by no means to be confounded with the paper-fuelled nautilus, notwithstanding the great resemblance in the arms and body of the inclosed fish; nor is the cornu ammonis, so frequently found fossil, to be confounded with the thick-shelled nautilus, though the concatenations and general structure of the shell are alike in both; for there are great and essential differences between all these genera. There is a pretty copious and minute account of this curious animal in the Gentleman's Magazine, vol. xxii. p. 6, 7, 8, and 301, and vol. xxv. p. 128.