Part 16

ATRACTODON. Charlesworth. (Mag. Nat. Hist. 2nd series, Vol. 1. p. 218. ) A genus proposed for the admission of a singular fossil shell, found on the beach at Felix-stone, of which the following are the characters;--fusiform, aperture equalling the spire in length, terminating anteriorly in a slightly recurved canal; columellar lip smooth, curved, thickened posteriorly into a blunt tooth; spire obtuse.--Obs. This shell would be a Fusus were it not for the tooth on the posterior extremity of the columellar lip. The only species known is regularly striated in a spiral direction, and named A. Elegans.

ATRYPA, Dalman. A genus of brachiopodous bivalves, distinguished by the valves being nearly equal, and the umbones not separated by an intermediate area. A. reticulata, fig 302.

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.

AURICULATED. Some bivalve shells, such as Pecten, fig. 171, 172, have a flat, broad, somewhat triangular appendage on one or both sides of the umbones, called an auricle, or little ear. If on one side only, they are said to be uni-auriculated; if on both, they are said to be bi-auriculated.

AURICULACEA. Bl. The second family of the order Pulmobranchiata, thus described; "shell thick, solid; aperture more or less oval, always large, rounded anteriorly, and contracted by teeth or folds on the columella." This family is included in the genus Voluta of Linnæus, on account of the plaited columellar lip, a character by which that heterogeneous assemblage of shells is distinguished. It forms part of the family of Colimacea, Lam. from which they differ not only in general form, but also in the fact of the animals being partly amphibious, always living (according to De Blainville) on the sea shore, and being occasionally covered with water for a short time. It contains the genera Pedipes, Auricula, Pyramidella.

AURIFERA. Bl. OTION, Auct.

AURIFORM. (From Auris, an ear; forma, shape.) Ex. Haliotis, fig. 338.

AURISCALPIUM. Megerle. ANATINA, Lam.

AVICULA. Lam. (From Avis, a bird). Fam. Malleacea, Lam. Margaritacea, Bl.--Descr. Inequivalve, inequilateral, foliaceous, subquadrate, oblique, pearly; hinge rectilinear, lengthened into auricular appendages, with a small indistinct tooth in each valve, an elongated, marginal, ligamentiferous area, and an hiatus in the left valve, for the passage of a byssus; one circular muscular impression, near the centre of each valve, with a series of smaller ones arranged in a line towards the umbones.--Obs. The Meleagrinæ of Lamarck, Margaritiferæ, Schum. included in this description, consist of the more rounded species, and do not present the elegant obliquity of form, nor the wing-like auricles from which the genus Avicula receives its name. The Aviculæ are pearly within. From A. margaritifera, a young specimen of which is figured in the plates, fig. 164, is obtained oriental pearls. This is an example of Meleagrina. A. Hirundo, fig. 163, belongs to the genus Avicula of Lamarck. It is, however, needless to continue the separation. Aviculæ are from E. and W. Indies, Mexico, Coasts of the Pacific, Mediterranean, British Islands, &c. Fossil species occur in the London clay, &c.

AXINUS. J. Sowerby.--Descr. Equivalve, transverse; posterior side very short, rounded, with a long ligament, placed in a furrow, extending along the whole edge; anterior side produced, angulated, truncated, with a flattish lunule near the beaks. The late Mr. James Sowerby, who described this shell in the Mineral Conchology, did not consider his genus as established, not having seen the hinge.

AXIS. The imaginary line, round which the whorls of a spiral shell revolve. The extremities of the axis are pointed out in fig. 379, by the letters, a. a. See "COLUMELLA."

AZECA. Leach. Fam. Colimacea, Lam.--Descr. "Animal like Bulinus, with subcylindrical, rather obtuse shell, covered with a polished periostraca (epidermis); aperture pear-shaped, curved and pointed at the top; the margin thick, obtuse, united all round and toothed; the axis imperforated." Gray's edition of Turton's British Shells, page 189.--Obs. The Turbo Tridens of Montagu, upon which this genus is founded, resembles Bulinus lubricus in general form and character. Both these shells differ from the true Bulini in having the peritreme entire, and in being pellucid and glossy. Azeca differs from Bulinus lubricus in having three teeth in the aperture, two on the inner lip and one on the outer. Not seeing the necessity for creating a genus on grounds so slight, I have simply transcribed the description given above, leaving others to form their own conclusions as to the propriety of separating this shell from the genus Bulinus. Britain, Central and Southern Europe. Azeca Tridens, fig. 290.

AZEMUS. Ranzani. CONIA, Leach.

BACULITES. Lam. Fam. Orthocerata, Bl. Ammonacea, Lam.--Descr. Straight, conical, tubular, laterally compressed; chambers divided by very sinuous lobed septa, the last elongated; aperture elliptical; siphon dorsal.--Obs. This genus differs from Orthoceras in the same manner in which Ammonites differs from Nautilus, having its septa sinuated and branched. A Baculite might be described as a straight Ammonite. This genus is known only in a fossil state. It is found in the Cretaceous Limestone of Maëstricht and Valognes. Fig. 484. B. Faujasii.

BALANUS. Brug. (an Acorn; "gland de Mer." Fr.) Order Sessile Cirripedes, Lam. Fam. Balanidea, Bl.--Descr. Shell composed of six valves articulated to each other side by side in a circle, by the insertion of lamina; closed at the base by a flat, cylindrical or cup-shaped valve, by which it is generally attached; and at the apex by a conical operculum, consisting of four valves in anterior and posterior pairs. Each valve of the shell is divided into a rough triangular portion pointed towards the apex, and a flat area on each side.--Obs. This description includes the Acasta of Leach, which growing in sponges, has the base cup-shaped; Conoplæa of Say, which being attached to the stems of Gorgonia and sea-weeds has the base elongated and lanceolate, and Chirona, Gray. Balanus is the only genus of Sessile Cirripedes the shells of which consist of six parietal valves, except coronula, which has no shelly base, is flatter, and has the valves of the operculum placed horizontally. The Balani are common in all seas, adhering to rocks, corals, floating timber, and to each other. The fossil species are found in the newest strata, at Bordeaux, Paris, &c. Fig. 25. B. Tintinnabulum; 26. Acasta Montagui; 27. Balanus galeatus, Conoplæa, Say.

BALANIDEA. Bl. The second family of the class Nematopoda, Bl. corresponding with Sessile Cirripedes, Lam., and consisting of Coronular Multivalves, which are fixed, and in a manner soldered to submarine substances, by the base of the shell; as distinguished from the Lepadicea, Bl., Pedunculated Cirripedes, Lam., which are attached by a fleshy stalk. The Balanidea are composed of two sets of valves, besides the shelly plate or base on which they rest. The first, called the Parietal valves, are arranged so as to surround the body of the animal; the second, called the Opercular valves, are placed horizontally, so as to cover the aperture.

BALEA. Gray. Fam. Colimacea, Lam.--Descr. Spiral, turrited, concentrically striated, sinistral, and covered with a thin brown epidermis; spire composed of numerous whorls, gradually increasing in size; aperture small, sub-quadrate; peritrême entire, slightly thickened, with a very slight fold on the columella; axis perforated.--Obs. A genus of small land shells, found in moss at the roots of trees in Britain, not very nearly resembling any other land shells, except Clausilia, from which they differ in not having the clausium. They have been placed in Helix by De Ferrusac, and in Pupa by Draparnaud. B. fragilis, fig. 296. Helix perversa, Fer. Pupa perversa, Drap.

BARBATA. Humphrey. UNIO, Lam.

BARNACLES. PENTELASMIS, Auct. (fig. 34.) Called Anatifa, by Linnæus and Lamarck, from the ancient notion that they were the eggs or embryo of the Barnacle Duck. See ANATIFER.

BASE. In all shells which are attached to sub-marine substances, the base is that part of the shell which forms the point of attachment,--as for instance, the attached valve of Spondylus, the basal plate of Balanus, the lower part of the peduncle of Pentelasmis; in Unattached Bivalves, the margin opposite to the umbones, where the foot of the animal, or the part analogous to it, protrudes; in spiral univalves, the aperture, which rests on the back of the animal when walking. Lamarck and some other authors have used the term base as simply opposed to apex, and apply it to the anterior of the aperture.

BATOLITES. Montf. HIPPURITES, Auct.

BEAK. The Apices, or points of the valves of a bivalve shell, generally termed UMBONES, in descriptions. Also any part which is rostrated or drawn out like a beak.

BEAKED. See BEAK and ROSTRATED.

BEAR'S-PAW-CLAM. The common name for Hippopus maculatus, a representation of which is given in the plates, fig. 156.