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.