ARGONAUTA. id 



ARCTICA. Schum. Cyprina Icelandica, Auct. 



ARCUATED. (Arcus, an arch.) Bent in the form of an arch, as 

 Dentalium, fig. 2. 



AREA. A flat apace or disc, on any part of a shell. As for instance, 

 the triangular space on the hinge of Area, fig. 132, and 

 Spondylus. 



ARENACEOUS. (Arena, sand.) Of a sandy texture, as the sand 

 tubes surrounding the bodies of some of the Annellides, named 

 Arenaria on this account. But the word is more commonly 

 used to intimate the habits of the animal, burrowing with its 

 shell in the sand. 



ARETHUSA. Montf. A genus of microscopic Foraminifera. 



ARGONAUTA. Auct. Commonly called the "Paper Sailor." 

 Fain. Pteropoda, Bl. Order Cepholopoda 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 ; peritreme acute, interrupted by the 

 body whorl. — Obs. The exquisitely beautiful, light and delicate 

 fabrics included under the above name are inhabited by a mollus- 

 cous animal named the Ocythoe, which is provided with tubercu- 

 lated 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 Mediter- 

 ranean 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 dis- 

 cussion, 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 Agonaut is the 



