VOLVARIA. Lam. (_Volva_, a shuttle.) _Fam._ Columellaria, Lam.--_Descr._ Cylindrical, convolute, spirally striated; spire very short, nearly hidden; aperture narrow, as long as the whole shell; columella with three oblique plaits; outer lip dentated.--_Obs._ The Volvaria are only known in a fossil state, and resemble some species of Bulla in general form, but are distinguished by the plaits on the columella. Fig. 439, V. concinna. VOLUTELLA. Sw. (_A little volute._) A genus composed of those species of MARGINELLA, Auct. which have the spire concealed, and the aperture smooth within. Fig. 438, PERSICULA of Schumacher. VOLUTILITHES. Sw. (_Voluta_, and [Greek: lithos], _lithos_, a stone.) A genus composed of some fossil species of Voluta, which have the plaits on the pillar generally numerous, indistinct, and sometimes wanting altogether, with a pointed spire. Fig. 436, V. spinosa. VOLUTION. See WHORL. VORTICIALIS. Lam. A genus of microscopic Foraminifera. VULSELLA. Lam. (_A little tongue._) _Fam._ Ostracea, Lau. Margaritacea, Bl.--_Descr._ Equivalve, irregular, longitudinal, compressed, oblong; umbones separated by a slight area in both valves; hinge with a large pit in the centre, containing the cartilage, the ligament being spread over the areas; muscular impressions, one on each valve, sub-central, oblong.--_Obs._ This genus differs from Ostræa in the equality of the valves, and in having a hollow pit in the hinge for the cartilage. Vulsella lingulata, fig. 185. WATERING-POT. Aspergillum, fig. 44, commonly so called on account of the resemblance of its perforated termination to that of the spout of a watering-pot. WENTLE TRAP. Scalaria pretiosa, commonly so called. WHORL. A complete turn or revolution round the imaginary axis of a spiral shell. The last whorl is called the _body-whorl_. The whorls are described as _non-contiguous_, when they do not touch each other; _continuous_, in the opposite case. _Depressed_ when they are flat. They are _angulated_, _heeled_, or coronated; _distinct_, or indistinct. They are sometimes, as in Cypræa, hidden by the last whorl. XYLOPHAGA. Sow. ([Greek: xulon], _zylon_, wood; [Greek: phagô], _phago_, to eat.) _Fam._ Tubiscolæ, Lam.--_Descr._ Equivalve, globose, closed at the back; with a large, angular hiatus in front; hinge with a small curved tooth advancing from beneath the umbones in each valve.--_Obs._ This shell, which is found in a cylindrical cavity, eaten in wood by the animal, resembles Teredo, but has not the shelly tube, nor the posterior hiatus. X. dorsalis, fig. 50, 51. XYLOTRYA. Leach. XYLOPHAGA, Sow. ZONITES. Montf. A genus formed of Helix Algira, and other similar species with depressed spires and large umbilici; included in the sub-genus Helicella. Fig. 279.