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.