ISOCARDIA. Lam. ([Greek: Isos], _isos_, similar; [Greek: Kardia], _cardia_, heart.) _Fam._ Cardiacea, Lam. Chamacea, Bl.--_Descr._ Cordiform, regular, equivalve, ventricose, with distant, diverging, involute, free umbones; hinge with two compressed cardinal, and one distant, compressed lateral teeth in each valve; ligament external, bifid, diverging in the direction of the umbones.--_Obs._ The shells composing this genus are remarkable for the beautiful curvature of the diverging umbones. European and Chinese Seas. Fig. 126, I. Moltkiana. KEEL. A flattened ridge, resembling the keel of a ship. As that on the back of Carinaria vitrea, fig. 488, and those on the whorls of some spiral shells. A shell characterized by a keel or keels is said to be carinated. KELLIA. Turton, MYA Suborbicularis, Montague. LABIS. Oken. MONODONTA, Lam. LABIUM, or inner lip,--is used to express that side of the aperture which is nearest to the axis and generally contiguous to the body whorl. The lower part of this, when sufficiently distinct from that part which overwraps the body whorl, is called the Columella. LABRUM, or outer lip,--is the edge of the aperture at the greatest distance from the axis. LACINEA. Humph. CHAMA, Lam. LACUNA. Turt. _Fam._ Turbinacea, Lam.--_Descr._ Globose, thin, covered with a smooth epidermis; spire short, consisting of few rapidly increasing whorls; aperture semilunar, rounded at the extremities; columella oblique, reflected over part of the umbilicus; umbilicus forming a lengthened area behind the columella. Northern shores. Fig 364, L. Pallidula. LAGENULA. Montf. A genus of microscopic Foraminifera. LAMELLATED. (_Lamella_, a thin plate.) When the layers of which a shell is composed, instead of being compacted into a solid mass, are separated, overlying each other in the manner of tiles, with the edges prominent, the structure is said to be lamellated or foliaceous. LAMELLIBRANCHIATA. Bl. The third order of the class Acephalophora, Bl. consisting of bivalve shells, divided into the families Ostracea, Subostracea, Margaritacea, Mytilacea, Polydontes, Submytilacea, Chamacea, Conchacea, Pylorides, Adesmacea. LAMELLIPEDES. Lam. (_Lamella_, a thin plate, _pes_, a foot.) The third section of the order Conchifera Dimyaria, containing bivalves, with the foot of the animal broad and thin; divided into the families Conchacea, Cardiacea, Arcacea, Trigonacea, Nayades. Fig. 111. to 152. LAMPAS. Montf. LENTICULINA, Bl. A genus of microscopic Foraminifera.