MELO. Brod. (_Melo_, a melon.) _Fam._ Columellaria, Lam.--_Descr._ Light, ventricose, oval, with a light greenish brown epidermis, spire short, papillary, regular, sometimes hidden by the last whorl; aperture large, nearly as long as the whole shell, emarginated anteriorly; outer lip thin; columella slightly curved, with four or five laminar, oblique, prominent plaits.--_Obs._ The genus Melo has been separated from _Voluta_ principally on account of the largeness of the aperture, the lightness of the shell and the thinness of the outer lip. Melo differs from Cymba in the regularity of the spiral apex, and in the greater rotundity of the shell. The Melons are beautifully coloured large shells, found in the seas of the old world. The Melo Indicus has a certain resemblance to a Melon. Fig. 435. M. Æthiopicus. MELONIA or MELONITES. A genus of microscopic Foraminifera. MERCENARIA. Schum. VENUS Mercenaria, Auct. The Money shell which passes current for cash, under the name "Wampum," among the North American Indians. MERETRIX. Lam. Original name for Cytherea, Lam. MEROE. Schum. CYTHEREA Meroe, sulcata, scripta, hians, Auct. and similar species. Fig. 117, a. MESODESMA. Desh. ERYCINA, Lam. according to G. B. Sowerby. MESOMPHYX. Rafinesque. A genus proposed to be separated from HELIX, Auct. MICROTOMA. Sw. A genus of "Purpurinæ," Sw. thus described, "Pillar very broad and curving inwards; aperture effuse; the notch at the base small and nearly obsolete; spire very short, patula. Mart. 69. f. 758, 759. persica. En. Méth. 397. f. 1. unicolor. _Sw._ Chem. f. 1449. Sw. p. 301." Purpura Persica. Fig. 414. MILIOLA. Lam. A genus of microscopic Foraminifera. MISILUS. Montf. A genus of microscopic Foraminifera. MITRA. Lam. (_Mitre._) _Fam._ Columellaria, Lam. Angyostomata; Bl.--_Descr._ Oblong, thick, covered with a light brown epidermis; spire long, turrited, acute; aperture emarginated anteriorly; outer lip thickened; columella with several oblique, thick plaits.--_Obs._ The pretty small shells composing this genus differ from Marginella, not only in general form, but in the outer lip not being reflected. Some species of Voluta, of a more elongated shape than the rest, present a near approach to the most ventricose of the Mitræ. The apex of Mitra, however, is always acute, while that of Voluta is generally papillary. The aperture of the former is narrow and the inner lip thickened, the contrary being the case with the latter. The shells of this genus are varied in colouring which is generally rich; and also in form, some being angulated, some plicated, some coronated and others smooth. The species are mostly tropical; very few occur so far north as the Mediterranean. Fossil species are numerous in the Eocene beds. Fig. 431. M. Plicaria. Fig. 432. Conohelix marmorata, Sw.