Part 77

UNIVALVE. (Unus, one; valva, valve.) A shell consisting of a single piece, as distinguished from Bivalves and Multivalves, which are composed of two or more principal pieces. Spiral shells having an operculum, are called sub-bivalves by some authors.

UPPER-VALVE. The free valve in attached bivalves.

UVIGERINA. D'Orb. A genus of microscopic Foraminifera.

VAGINA. Megerle. SOLEN vagina, Auct.

VAGINULA. (A little sheath, the husk of corn.) Class, Pteropoda, Lam.--Descr. Pyramidal, slightly inflated in the centre, thin, fragile; aperture oblong, with the edges turned slightly outwards.--Obs. The little shells of this genus, which are only known in a fossil state, differ from Cuvieria in being pointed at the extremity. Found in the tertiary beds of Bordeaux. V. Daudinii, fig. 225.

VAGINULINA. D'Orb. A genus of microscopic Foraminifera.

VALVATA. Müll. Fam. Peristomata, Lam. Cricostomata, Bl.--Descr. Thin, turbinated; spire short, composed of from three to six rounded whorls; aperture circular; peritreme acute, entire; operculum horny, spiral.--Obs. This genus of small shells resembles Cyclostoma, from which the recent species may be known by the horny texture of the external surface, being fresh-water shells. The fossils of course belong to the fresh-water formations. V. piscinalis, fig. 322. Europe and North America.

VALVES. (Valva, a door, a folding piece.) The two pieces composing a bivalve shell, which close upon each other, turning upon a hinge consisting of a ligament, cartilage, and teeth. See BIVALVE, MULTIVALVE, and UNIVALVE.

VALVULINA. D'Orb. A genus of microscopic Foraminifera.

VARIX. (A swelling vein.) A varix is formed on the outer surface of a spiral shell, by the thickened, reflected edge of a former aperture, after fresh deposits of testaceous matter have increased the size by adding to the growth of the shell beyond it. In this manner there are frequently many varices, or edges of former apertures, in various parts of the spire and the body whorl. They are sometimes placed at regular distances from each other, as in Harpa, fig. 419; sometimes continuous, as in Ranella, fig. 394; sometimes discontinuous, as in Triton, fig. 398; sometimes ramose, as in Murex, fig. 395; sometimes simple, as in Scalaria, fig. 351; sometimes spinose, as in Murex spinosus. The term varix has also been applied to any swelling ridge, such as that on the lower part of the columella of Ancillaria, fig. 456.

VELATES. Montf. NERITINA perversa, Auct. Fig. 326.

VELLETIA. Gray? A genus described as differing from ANCYLUS in being dextral. VELLETIA lacustris, ANCYLUS lacustris, Auct. fig. Sowerby Gen. fig. 2.

VELUTINA. Auct. Fam. Macrostomata, Lam.--Descr. Sub-globose, covered with a velvety epidermis; spire short, composed of two rapidly enlarged ventricose whorls; aperture large, sub-ovate; peritreme thin, entire, separated from the last whorl; columella tortuous, thin.--Obs. This shell does not resemble any other genus in the family. Fig. 337. Northern Seas.

VENERICARDIA. Lam. A genus composed of the shorter species of Cardita.

VENERIRUPIS. Lam. (From Venus and rupis, a rock.) The oblong species of Venus Auct. which live in cavities of rocks and stones. This genus is united by Sowerby with some other species of Venus under the name Pullastra. V. Vulgaris, fig. 97.

VENTRAL. (Venter, the belly.) The margin of a bivalve shell opposite the hinge. The under valve in Brachiopodous bivalves is the ventral valve. The ventral surface of an univalve spiral shell is that which faces the observer when the aperture is placed towards him. The ventral part of the whorls of symmetrical convolute shells, is the inner part, that which is nearest to the spire.

VENTRAL SIPHON. In symmetrical convolute univalves, is one placed near the inner edge of the whorls.

VENTRICOSE. (Ventricosus.) Swelled, rounded out, (bombé Fr.) as Harpa ventricosa, fig. 419.

VENUS. Auct. (Goddess of Beauty.) Fam. Marine Conchacea, Lam. Conchacea, Bl.--Descr. Equivalve, inequilateral, sub-globose, sub-ovate, transverse, externally rugose, striated, ribbed, cancellated or smooth; margins entire, simple, close; hinge with three more or less distinct cardinal teeth, diverging from the umbones in each valve; muscular impressions two, lateral, distant; palleal impressions sinuated posteriorly; ligament external.--Obs. This extensive genus, including some bivalves of splendour and beauty, justifying the name given to it, may be known from Cytherea by the absence of a lateral tooth, which is found near the cardinal teeth in the latter. Artemis is distinguished not only by its beautiful form, but by the deep angular sinus in the palleal impression. Fig. 119, 119 a. Found mostly in temperate and tropical climates.

VERMETUS. Adanson. Fam. Scalariana, Lam. Cricostomata, Bl.--Descr. Spiral at the apex, irregularly twisted towards the aperture; aperture round, small.--Obs. This shell resembles the Serpulæ in general appearance, although it is regularly spiral near the apex. The animal is known to be a true mollusc, rather nearly allied to that of the genus Dentalium, which is also placed wrongly in the Lamarckian system. Vermetus Lumbricalis, fig. 345. Coast of Africa.

VERMICULAR. (Vermicularis.) Worm-shaped, tubular, serpentine. Ex. Vermilia triquetra, fig. 7.

VERMICULARIA. Lam. VERMETUS, Adanson; afterwards VERMETUS, Lam.

VERMILIA. Lam. A genus composed of species of Serpula, which are attached by the whole length of the shell, no part being free. Vermilia triquetra, fig. 7.

VERTEBRALINA. D'Orb. A genus of microscopic Foraminifera.

VERTEX. Apex.

VERTIGO. Müll. Fam. Colimacea, Lam.--Descr. Cylindrically fusiform, sinistral, hyaline; aperture marginated, sinuated, denticulated on the inner edge; peristome sub-reflected.--Obs. This genus of minute land shells, resembles Pupa, but is a reversed, hyaline shell. Vertigo pusilla, fig. 293. Europe.

VERRUCA. Schum. CLITIA, Leach.

VESICA. Sw. A sub-genus of Bulinus, Sw. p. 360.