Part 41

IRREGULAR SHELLS, are those which, being attached to, or imbedded in other marine bodies, have no constant form, but are modified in shape according to the substances to which they are fixed, as the Chamacea, fig. 153 to 155.

IRUS. Oken. Comprehending PANDORA, PETRICOLA, SAXICAVA, &c.

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.

LAMPRODOMA. Sw. A genus of "Olivinæ," Sw. thus described:--"Mitriform; spire produced, conic; resembling MITRELLA in shape, but the suture is channelled; the aperture effuse at the base, contracted above; lower half of the pillar with 6 to 7 plaits. Volutella, Zool. Ill. ii. series, pl. 40. f. 1. (fig. 86. )" Sw. p. 321.

LAMPROSCAPHA. Sw. A sub-genus of "Anodontinæ," Sw. thus described:--"Shell not winged, elongate, pod-shaped; teeth none; bosses near the anterior extremity. Tropical America only? L. ? elongata. Sw. Zool. Ill. i. 176. ensiforme, Spix. Braz. Test. siliquosa. Braz. Test. pygmæa. Ib." Sw. p. 381.

LAMPROSTOMA. Sw. A sub-genus of Canthorbis (Trochus), described at p. 350, Lardn. Cyclop. Malac.

LAMPUS. Humph. TEREBRATULA, Lam.

LANCEOLATE. Lengthened like a lance.

LANISTES. Montf. Reversed species of AMPULLARIA, fig. 319.

LAPLYSIA. See APLYSIA.

LAPLYSIACEA. Lam. (properly Aplysiacea) A family belonging to the first section of the order Gasteropoda, Lam. containing the genera Aplysia and Dolabella. Fig. 254, 255.

LARVA. Humph. FISSURELLA, Lam.

LATERAL. (Latus, a side.) The lateral teeth are those which, taking their rise near the umbones, proceed to some distance towards the sides of the shell; as distinguished from the cardinal teeth, which receive their full developement close to the umbones. Lateral muscular impressions are those which are placed at a distance from each other, on the opposite sides of the shell.

LATIAXIS. Sw. A genus of "Eburninæ," Sw. corresponding with the genus Trichotropis. Sow. (Sw. Malac. p. 306.)

LATIRUS. Montf. A genus composed of species of FUSUS, Auct. which have an umbilicus and are turriculated.

LAURIA. Gray. A sub-genus of PUPA, containing P. umbilicata, &c. (Gray's Turton, p. 193.)