MITRA. 189 



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 « Purpurinae," Sw. thus de- 

 scribed, "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. Meth. 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 emargiiaated 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 ven- 

 tricose of the Mitrse. 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. Cono- 

 helix marmorata, Sw. 



