LICIUM. Humph. OVULA, Lam. (Ovulum.) LIGAMENT. (From _Ligo_, to bind.) The true ligament is always external, and serves the purpose of binding the two valves of a shell together externally by the posterior dorsal margins. There is another substance, called by Gray the _Cartilage_, which is elastic and of a condensed fibrous structure, placed within the ligament, either close to it, or at a more interior part of the shell; it is sometimes contained in a pit, formed for its reception, in the centre of the hinge. This substance, being elastic, keeps the valves open, unless drawn together by the counteracting force of the adductor muscles. When conchologists speak of a shell as having the ligament external, the real meaning is that these two substances are so close together as in appearance to constitute one body placed outside the shell so as to be seen when the valves are closed. When two ligaments are spoken of, as in Amphidesma, the meaning is that the cartilage occupies a separate place on the hinge. LIGAMENTIFEROUS. (_Ligamentum_, a ligament, _fero_, to bear.) Having or containing the ligament, as the cardinal pit in Mya, fig. 71. LIGULA. Leach. A genus containing the more rounded and less gaping species of LUTRARIA, Auct. Fig. 77, Lutraria Papyracea. LIGULATE. (_Ligula_, a slip, a shoe-latchet.) Thin, slender, like a slip, or neck of any thing, as the anterior muscular impression of Lucina, fig. 104. LIGUMIA. Sw. A sub-genus of Unio, thus described:--"Very long and pod-shaped; bosses depressed; cardinal teeth moderate. S. recta. Lam. vi. 1. p. 74." Sw. p. 378. LIGUUS. Montf. A genus containing species of ACHATINA, Auct. which have rounded apertures and lengthened spires, differing from his POLYPHEMI, which have lengthened apertures. A. virginea, Auct. fig. 286, is the type of this genus. LIMA. Brug. (_Lima_, a file.) _Fam._ Pectinides, Lam. Subostracea, Bl.--_Descr._ Equivalve, inequilateral, compressed, oblique-auriculated, oval, radiately ribbed or striated, imbricated, covered with a light brown epidermis; hinge with a triangular disc between the umbones, divided in the centre by a triangular ligamentary pit without teeth; muscular impression one, sublateral, sub-orbicular.--_Obs._ The shells thus described are marine, two or three species being found on our coasts, and fossil species occurring in Lias, inferior Oolite, Calcaire-grossiér, &c. They differ from Pecten in having a wide hiatus for the passage of a byssus, by which they are occasionally attached, and also in the triangular disc, which separates the umbones. The animal makes use of the valves of his shell as natatory organs, working them like fins or paddles, and by this means proceeding at a rapid rate through the waters. L. Squamosa, fig. 174.