ATTACHED. Shells are attached to marine substances by various means; in some cases by a _byssus_, or a bunch of tendinous fibres passing through an opening between the valves, which gape at their margins to admit a free passage, as in the genera Byssoarca and Mytilus. In other cases the byssus is of a more compact substance, and passes through a perforation in the shell itself. This is the case with many of the brachiopodous shells, in some species of which the perforation is in the point of the umbones, a specimen of which is represented in the Introduction. This species of attachment does not keep the animal motionless, although it is confined to a particular spot. Other shells are attached by a portion of their own substance, as in Chama, Spondylus, Serpula, &c. in which instances, the attached valve is motionless, and is termed the under valve. The Pedunculated Cirripedes are attached by a tubular tendinous process, called a peduncle. ATTENUATED. Drawn out, long, thin, tapering, as the extremities of Ovulum Volva, fig. 442. ATYS. Montf. A generic name including those species of BULLA, which are described as "convolute, with the last whorl covering the rest and hiding the spire, the apex rounded at both ends." Bulla Naucum, Auct. fig. 250. AURICLE. (A little ear.) See AURICULATED. AURICULA. Lam. (Dim. from _Auris_ an ear.) _Fam._ Auriculacea. Bl. Colimacea, Lam.--_Descr._ Oval or oblong, cylindrical or conical; aperture long, narrow, generally narrowest in the centre; rounded anteriorly, with two or three strong folds on the inner lip, and the outer lip thickened, reflected or denticulated; spire short, obtuse, epidermis horny, brown.--_Obs._ The above description includes the A. coniformis, f. 298. and several other conical species with narrow apertures which formed the genus _Melampus_, Montf. and _Conovulus_, Lam. The latter author suppressed his genus on ascertaining the Conovuli to be land shells. We exclude, however, the A. Dombeyana, Lam. f. 300. and several similar species, which being more rounded, having thin outer lips and but one fold on the columella, are described under the generic name _Chilina_, Gray. It appears rather doubtful whether the Auriculæ are marine or fluviatile, but the animals appear to be amphibious. The Auriculæ are principally found in Salt Marshes of Tropical climates, some small species are found on the Southern European Coasts, as far north as Britain and south as Tierra del Fuego. The Auriculæ formed a part of the genus Voluta of Linnæus, f. 297. A. Judæ, f. 298. A. Coniformis.