ARGONAUTA. Auct. Commonly called the "Paper Sailor." _Fam._ Pteropoda, Bl. _Order_ Cephalopoda Monothalamia, Lam.--_Descr._ Light, thin, transparent or nearly so, symmetrically convolute, carinated by a double row of tubercles, terminating smooth or tuberculated ribs radiating towards the centre; aperture large, elongated; peritrême acute, interrupted by the body whorl.--_Obs._ The exquisitely beautiful, light and delicate fabrics included under the above name are inhabited by a molluscous animal named the _Ocythöe_, which is provided with tuberculated arms. These, hanging over the sides of the aperture, give to the whole the appearance of a vessel propelled by oars: a poetical illusion further heightened by the broad, flat membranes of the two arms, which, when vertically expanded, present an idea of sails. Pliny has described the Nautilus (the name has been changed by the moderns) as sailing gracefully on the Mediterranean waters; and Pope has versified the idea in the well known lines "Learn of the little Nautilus to sail, Spread the thin oar and catch the driving gale." Scientific men have long been engaged in the interesting discussion, whether the animal really belongs to the shell in which it is found, or whether, having destroyed the rightful owner, it has possessed itself of the "frail bark." It is now, however, proved beyond the shadow of a doubt that the Argonaut is the testaceous part of the Ocythöe, and that the broad membranes which in some representations have been artificially placed as sails, are naturally bent backwards over the shell like the mantle of some other molluscs. The interesting experiments of Madame Power, in the Mediterranean, have contributed very materially to lead the investigations of Naturalists to a satisfactory conclusion. This lady kept a cage under water, in which Argonautæ were bred in great numbers, giving her an opportunity of tracing the gradual development of the shell in all its stages, from the elastic and transparent nucleus to the full grown "Paper Sailor." Fig. 485. ARIANTA. Leach. A sub-genus of land shells, containing HELIX arbustorum, Auct. (Gray, Turton, p. 137.) ARION. A genus of slugs which have no shells. ARROW-HEADS. One of the names by which fossils of the genus Belemnites were formerly known. ARTEMIS. A genus of bivalve shells, distinguished from those of the genus Venus, by having a rounded, denticular form, and a deep, angular sinus in the palleal impression. This does not appear to me to be a sufficient ground of generic distinction, the palleal impressions of the Veneres being subject to great variations. British, also from West Indies, South America, Australia, &c. A. lincta, fig. 118.