Part 12

AGATHIRSES. Montf. SILIQUARIA, Auct.

AGINA ----? Belongs to SAXICAVA, Auct.

AKERA. Bl. The fourth family of the order Monopleurobranchiata, Bl. containing the genera Bulla, Bullæa and Bellerophon, which, excepting the last, constitutes the family Bullæana, Lam.

AKERA. A genus of extremely light, horny shells, resembling BULLA, from which it differs, in the outer lip being separated from the body whorl, which is elastic. Ex. Bulla fragilis, fig. 247.

ALÆA. Jeffrey's. A genus of minute land shells, resembling Vertigo, but separated because they are dextral, while Vertigo is sinistral. Ex. fig. 292. A. marginata, Pupa marginata, Drap. found in marshy ground, roots of trees, moss, &c. Britain and Southern and Central Europe.

ALASMODON. Say. A division of the genus UNIO, Auct. consisting of those species which have cardinal, but no lateral teeth. Ex. A. complanatus, fig. 141. North America and Europe.

ALATÆ. Lam. A family of the order Trachelipoda, Lam. containing the following genera which may be thus distinguished.

1. ROSTELLARIA. Sinus close to the canal; including Hippochrenes, and Aporrhais, Fig. 402 to 404.

2. STROMBUS. Sinus not close to the canal. Fig. 406.

3. PTEROCERAS. Same, digitated. Fig. 405.

ALATED. (From Ala, a wing.) Winged, a term applied to shells, when any portion of them is spread out in any direction, as in fig. 403. Hippochrenes, Montf. and fig. 147, Unio Alatus.

ALCADIA. Gray? (B. M. Syn. p. 134) Helicinæ which have a notch in the aperture. A distinction which it is impossible to maintain. See HELICINA.

ALATUS. Humphrey. STROMBUS, Auct.

ALECTRION. Montf. BUCCINUM Papillosum, Auct. fig. 422.

ALEPAS. Rang. A genus of Pedunculated Cirripedes without a shell.

ALVEOLINA. D'Orbigny. A genus of microscopic Foraminifera.

AMALTHUS. Montf. A. margaritaceus, Montf. is a species of AMMONITES described as very flat, keeled, with an angular aperture. It belongs to the family Ammonacea, Lam.

AMARULA ----? A genus composed of MELANIA Amarula, Auct. and similar species.

AMBIGUÆ. Lam. The fourth section of the order Conchifera Dimyaria, containing the family Chamacea, fig. 153 to 155.

AMICULA. A genus formed for the reception of CHITON amiculatus, Auct. the valves of which are covered by an integument; so as to be completely hidden externally.

AMIMONUS. Montf. CONILITES ungulatus, Knorr. A species distinguished only by being slightly curved; Fam. Orthocerata, Lam.

AMMONACEA. Bl. The fourth family of the order Polythalamia, Bl. or chambered shells, described as thin, chambered, discoidal, convolute, symmetrical, generally compressed, with visible whorls. This last character is used in De Blainville's System to distinguish the Ammonacea from the Nautilacea. This family contains the genera Discorbites, Scaphites, Ammonites, and Simplegas.

AMMONACEA. Lam. The seventh family of Polythalamous Cephalopoda, Lam. containing the genera Ammonites, Orbulites, Ammonoceras, Turrilites and Baculites, to which may be added Amalthus, Simplegas, Ellipsolites, Nautellipsites, Hamites, Icthyosarcolites, and other genera mentioned in the list of figures 477 to 484.

AMMONITES. Auct. (from Jupiter Ammon.) Fam. Ammonacea, Lam. and Bl.--Descr. Symmetrical, convolute, discoidal, orbicular; chambers numerous, divided by lobated, branched or sinuous septa, perforated by a Siphon; aperture generally more or less modified by the last whorl. The fossils of the secondary strata which compose this genus are numerous and well known; they are vulgarly termed "snake-stones," and some of them are extremely beautiful, particularly when the internal structure is exhibited by a section. There is some difficulty in distinguishing them from the Fossil Nautili, for although the whorls, being visible and the Septa sinuous, may be taken as the characteristics of the Ammonites, yet there are several species which partake the characters of both. The Orbulites of Lamarck (fig. 479) for instance, have sinuous septa like Ammonites, but the last whorl covers those which precede it as in Nautilus. Simplegas Montf. and Bl. (fig. 475) has the whorls visible externally and the septa simple. Ammonites is figured in the plates (478).

AMMONOCERAS, or AMMONOCERATITES. Lam. (from Ammon & [Greek: Keras], ceras, horn.) The shells described under this Lamarckian genus present an anomaly which is considered by Mr. G. B. Sowerby, sen., as merely accidental. They resemble the Ammonites in internal structure, but instead of being spirally convolute they are merely curved like a horn. Ex. fig. 477, copied from De Blainville.

AMNICOLA. The name of a genus mentioned in the family of Melaniana in the conchological part of the Synopsis of the British Museum, but unexplained.

AMPHIBOLA ----? The same as AMPULLARIA, Auct.

AMPHIBULIMA. Lam. SUCCINEA Patula, Auct. (fig. 266.) was first published in the Ann. du. Mus. D'Hist. Nat. under the name Amphibulima cucullata. The generic name was afterwards abandoned by its author, and the species stands in his system as Succinea cucullata. West Indies.