Part 11

ABSIA. Leach. LITHOTRYA, Sowerby. Fam. Pedunculated Cirripedes.

ACAMAS. Montfort. BELEMNITES multiforatus, Blainville. A species described as being perforated at the apex, by a stellated perforation. No species of Belemnite at present known agreeing with the description; it is supposed to have been taken from a broken specimen.

ACANTHOCHETES. A name given to a species of Chiton having bunches of bristles at the sides of the valves.

ACARDO. Commerçon. Described from a pair of bony plates, taken from the vertebræ of the Whale, and mistaken for a bivalve shell, destitute of a hinge.

ACARDO. Swainson. A generic term applied by Swainson to the nearly toothless species of Cardium, named C. edentulum by some authors; C. Greenlandicum by others: fig. 123*.

ACASTA. Leach. Order, Sessile Cirripedes, Lamarck. BALANUS Montagui, Sowerby. A small genus separated from Balanus, on account of the cup-shaped base, but re-united by Sowerby, who shews, in his Genera of Shells, that this is a merely accidental circumstance, resulting from the situations in which the shells acquire their growth. If, for instance, the Balanus be attached to a flat surface, in an open situation, the base will be short and flat; if it be placed in a hollow among other growing substances, it will be lengthened out in order that the aperture of the shell may be even with the outer surface of the surrounding mass; and if, as in the Acastæ, it be imbedded in a soft and loose substance, the base, being left to itself, will take a regular form. The Acastæ are found imbedded in sponges. Ex. Balanus Montagui, of Great Britain, fig. 26. Also found in the Pacific ocean and Philippines.

ACAVUS. Montfort. Fam. Limacinea, Blainville; Colimacea, Lamarck. A division of the genus Helix, which may be considered synonymous with De Ferrusac's sub-genus Helicogena. De Montfort has given H. Hæmastoma, as an example. Fig. 267.

ACCESSARY VALVES, are the smaller or less important testaceous plates, found on the hinge or dorsal margins of the true valves of some shells. Example, the small plates on the hinge of Pholas, fig. 55, a. The Pholades were placed by Linnæus and Bruguière among multivalve shells.

ACEPHALOPHORA. Blainville. (a, without; [Greek: kephale], head.) The third class of the type Malacozoaria, Bl. including all bivalve shells, the animals of which have no distinct head. This class corresponds with the Conchifera of Lamarck, and is divided into the orders Palliobranchiata, Rudistes, Lamellibranchiata, and Heterobranchiata, the last of which contains no genera of testaceous Mollusca.

ACHATINA, Auctorum. Fam. Colimacea, Lam. (from Achates, an agate.) Fam. Limacineæ, Bl. Gen. POLYPHEMUS, Montf.--Descr. Shell oval or oblong, sub-turrited, light, thin; aperture oval, or pyriform; outer lip sharp; columella smooth, tortuous, truncated, so as to form a notch at its union with the outer lip.--Obs. It is from this notch that we are enabled to distinguish Achatinæ from Bulini, which, moreover, generally have a reflected outer lip. The Polyphemi of Montfort have an undulation in the centre of the outer lip. Achatina Virginea, fig. 286. Polyphemus Glans, fig. 288. These land shells are found in various parts of the globe, but attain the greatest size and richness of colouring in tropical climates; particularly in the West India Islands.

ACHATINELLA. SOW. A small group of shells, differing from Achatina in having the inner edge of the outer lip thickened, and a slight groove near the suture of the spire. Fig. 287. Sandwich Islands.

ACHELOIS. Montf. CONILITES Achelois. Knorr. Supp. T. 4, fig. 1.

ACICULA. Nilson. ACHATINA Acicula, Auct. CIONELLA, Jeffreys.

ACIONA. Leach. A genus described by De Blainville as consisting of those species of Scalaria, the whorls of which do not touch each other. If this account be correct, the genus proposed by Leach will include the typical species of Scalaria, such as S. pretiosa.

ACME. Hartmann. A genus formed of TURBO fuscus, Walker. AURICULA lineata, Drap. thus described--"Shell sub-cylindrical, with a blunt tip; mouth ovate, simple, thin, slightly reflected over the pillar, forming a slight perforation." The animal is said to resemble a Cyclostoma, but has no operculum. Auricula lineata, Drap. Hist. 57, t. 3, fig. 20, 21. Southern Europe.

ACTEON. Montf. TORNATELLA, Lam.

ACTINOCAMAX. Stokes. A genus of Belemnitiform Fossils.

ACULEATED. Beset with sharp spines, as the margin of Chiton aculeatus, fig. 227.

ACUMINATED. Terminating in a point, as the apex of Melania subulata, fig. 313.

ACUS. Humphrey. TEREBRA of Lamarck.

ACUTE. Sharp, pointed, or sharp-edged.

ADDUCTOR MUSCLE. That which draws the two valves of a shell together, and leaves a mark on the inner surface of each, called the MUSCULAR IMPRESSION.

ADELOSINA. D'Orb. A genus of microscopic Foraminifera.

ADESMACEA. Bl. (a, without; [Greek: Desma], desma, ligament.) The 10th family of the order Lamellibranchiata, Bl. composed of Mollusca which either bore tubular dwellings in rocks, wood, &c. or live in testaceous tubes, their shells being consequently destitute of the hinge ligament. The action of opening and shutting the valves being limited to the narrow space to which they are confined, or else the valves themselves being soldered into the tube, renders it unnecessary for them to have a ligament to keep them in their places. The genera Pholas, Teredina, Fistulana, and Septaria, belong to this family, which corresponds in part with the families Tubicolaria and Pholadaria, of Lamarck.

ADNA. Leach. One of the genera separated by Leach from Pyrgoma, and characterized as consisting of an upper valve, supported on a funnel-shaped base, which is not buried in the coral to which it is attached, like Pyrgoma, but is seen externally. The operculum consists of four valves. Adna, fig. 32. British Channel and Mediterranean.

ADNATE. A term applied by some authors to those shells belonging to the family of Unionidæ, which have the valves joined together at the dorsal margin, not like other bivalves, by a distinct ligament, but by the substance of the shell itself, the valves appearing to grow together in such a manner that they cannot be separated without one of them being broken as will be seen in our figure of Dipsas plicatus, fig. 142. This circumstance has been made the foundation of specific and even generic distinctions, for which however it is insufficient, because many species which when young are "adnate," when fully grown have their valves joined together only by a ligament.

ÆGLIA. Say. A division of "Unionidæ," described as having the "shell cuneate; bosses prominent; cardinal teeth much compressed, placed on one side of the bosses. Æglia ovata, Say. Occidens Lea. Am. Tr. iii. pl. 10." Lardner's Encyclopedia of Malacology.

AGANIDES. Montf. ORBULITES, Lam.