VEXILLA. Sw. A genus of "Nassinæ," Sw. thus described: "General shape of _Purpura_, the inner lip flattened and depressed; the outer, when adult, thickened, inflected and toothed; aperture wide; picta _Sw._ Chem. pl. 157, f. 1504-5." Sw. Malac. p. 300. VIRGULINA. D'Orb. A genus of microscopic Foraminifera. VITRELLA. Sw. A sub-genus of "Bullinæ," Sw. Lardn. Cyclop. Malac. p. 360. VITRINA. Drap. (_Vitreus_, glassy.) _Fam._ Limacinea, Lam. and Bl.--_Descr._ Ovate, thin, glassy, fragile; spire short; last whorl large; aperture wide, transverse; peritreme simple; columella spiral, linear.--_Obs._ This genus of land-shells is not known in a fossil state. The recent species are found among moss and grass, in shady situations. De Ferussac has divided this genus into Helicolimax, fig. 263, and Helixarion, fig. 262. VITULARIA. Sw. A genus of "Muricinæ," Sw. thus described: "General habit of _Muricidea_, but the inner lip is depressed and flattened as in the _Purpurinæ_; varices simple, nearly obsolete. Tuberculata, Sw. En. M. 419. fig. 1. (_Murex vitulinus_, Auct.)" Sw. p. 297. VIVIPARA. A generic name given by Montfort, and retained by some authors for PALUDINA, Lam. on account of the animals being _viviparous_, i. e. the young being perfectly formed before they leave the ovaries. VIVIPAROUS. See VIVIPARA. VOLUTA. Auct. (_Volvo_, to revolve.) _Fam._ Columellaria, Lam. Angyostomata, Bl.--_Descr._ Sub-ovate, rather angulated, thick, generally tuberculated, smooth; spire short, conical, with a mammillated apex; aperture generally angulated, large, terminating anteriorly in a deep notch; columella smooth, with several plaits, of which the lowest is the largest; outer lip thickened within.--_Obs._ The genus Voluta, as left by Linnæus, is only characterized by the folds on the columella, and includes many shells which, although they agree in this respect with the genus, are yet quite opposite to each other in all other characters. Thus the Auriculæ, which are land shells, and have the aperture entire, are mixed up with others which are marine, and have a canal, as Turbinellæ, and the Fasciolariæ, and others which have merely a notch, as the true Volutes. This genus, as it is circumscribed at present, includes a great number of beautiful shells, most of which are rich in colouring. CYMBA and MELO have been separated by Mr. Broderip from the genus VOLUTA of Lamarck, for reasons stated in their respective descriptions. Fig. 443.