Part 48

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.

MITRELLA. Sw. A genus consisting of MITRA Fissurella, casta, Olivæformis, and similar species, described as "Rather small; olive-shaped; unequally fusiform; always smooth and polished, and sometimes covered with an epidermis; base obtuse and effuse; spire nearly or quite equal to the aperture; plaits of the pillar few, oblique, and extending beyond the aperture, which is smooth internally." Sw. p. 321. M. Fissurata, E. M. 371. f. 1. Olivarii, f. 2. Dactylus. 372. f. 5. Ex. Mitra bicolor.

MITREOLA. Sw. A genus of "Mitranæ," Sw. thus described: "Small; unequally fusiform; the base obtuse; inner lip, typically thickened, inflected, and either toothed or tuberculated; plaits on the pillar distinct, the inferior largest; tip of the spire sometimes papillary; aperture without either striæ or groove." Sw. p. 320, M. Monodonta, M. Terebellum. Zool. Illustr. II. 128. f. 1. f. 2.

MODIOLA. Lam. (Modiola, a little measure.) Fam. Mytilacea, Lam.--Descr. Equivalve oblique, cuneiform, inequilateral, thin, with the anterior side short and narrow, slightly gaping to admit the passage of a byssus, and the posterior side elongated, broad, sub-quadrate; hinge thin, toothless, rectilinear, with a long, partly external ligament; muscular impressions two in each valve; palleal impression irregular, not sinuated.--Obs. This genus differs from Mytilus, to which the common muscle belongs, in the anterior margin being rounded out beyond the umbo, which in Mytilus is terminal. The Lithodomi may be known from this genus by their cylindrical form. Fig. 160, M. Tulipa.

MOLLUSCA. (From Mollis, soft.) The twelfth class of invertebrated animals with univalve shells or none; divided into the following orders: Pteropoda, Gasteropoda, Trachelipoda, Cephalopoda, Heteropoda, fig. 220 to 488. The term mollusca is also used in a general sense to include the classes Conchifera and Mollusca of Lamarck, corresponding with the type Malacozoa of De Blainville.

MONEY COWRY. Cypræa Moneta, which passes current in some parts of Africa and the East Indies.

MONILEA. Sw. A sub-genus of Monodonta. Sw. p. 352.

MONOCEROS. ([Greek: Monos], monos, single; [Greek: Keras], ceras, horn.) Fam. Purpurifera, Lam.--Descr. Ovate, thick, covered with a brown epidermis; spire short, consisting of few whorls; aperture emarginated anteriorly; columella rather flat; outer lip thick, with a prominent tooth near the extremity.--Obs. This genus resembles Purpura, in every respect, except in having the tooth from which the name is derived. A catalogue of 16 species by Mr. Sowerby, sen. is published with figures of 14, in parts 58 to 67 of the Conchological Illustrations by the author. The species belong to the South American coasts of the Pacific Ocean.

MONOCONDYLÆA. D'Orb. A sub-genus of Uniones, described as equivalve, inequilateral, sub-rotund or angulated; hinge consisting of a large, obtuse, round cardinal tooth in each valve, with no lateral teeth. Monocondylæ (Unio) Paraguayana, D'Orb. fig. 149.

MONODONTA. Lam. ODONTIS, Sow. A genus separated from Trochus, Auct. on account of the tooth or notch with which the columella abruptly terminates. M. labeo, fig. 366.

MONOICA. Bl. The second sub-class of the class Paracephalophora, Bl. divided into the orders Pulmobranchiata, Chismobranchiata, Monopleurobranchiata, in the first section; and Aporobranchiata, Polybranchiata, Cyclobranchiata, Inferobranchiata, and Nucleobranchiata, in the second.

MONOMYARIA. Lam. ([Greek: Monos], monos, single; [Greek: muon], myon, muscle.) The second order of Conchifera, consisting of those bivalve shells which have but one principal muscular impression in each valve. The Monomyaria are thus divided: First section, containing the families Tridacnacea, Mytilacea, Malleacea; second section, containing the families Pectinides, Ostracea; third section, containing the families Rudistes, Brachiopoda.

MONOPLEUROBRANCHIATA. Bl. The second order of the first section of Paracephalophora Monoica. Bl. The animals are described as having the lungs branched, situated at the right side of the body and covered more or less completely by the operculiform mantle, in which there is sometimes enveloped either a flat or a more or less involute shell, with a large entire aperture. They have either rudimentary or auricular tentacula, or none. This order, which includes mollusca with haliotoid or patelliform shells, is divided into the following families: Fam. 1. Subaplysiacea; 2. Aplysiacea; 3. Patelloidea; 4. Acera.

MONOPTYGMA. Lea. A genus of small shells resembling Tornatella, but having a strong, oblique fold in the centre of the columellar lip. M. Elegans, fig. 344.

MONOTHALAMIA. ([Greek: Monos], monos, single; [Greek: thalamos], thalamos, chamber.) The second division of Cephalopoda, Lam. containing only one genus, namely Argonauta.

MONOTHYRA. A term used by Aristotle to designate spiral univalves.

MONOTIGMA. Gray. A genus founded on the species represented fig. 371. It is a turrited shell, but we are unacquainted with the characters of the genus.

MORIO. Montf. CASSIDARIA, Auct. C. Echinophora, fig. 407.

MOTHER OF PEARL. This beautiful substance, which is so much resorted to for ornamental purposes, constitutes the thickened coating of the internal surface of the shell named by scientific collectors, Meleagrina Margaritifera, commonly called the Pearl Oyster, a young specimen of which is figured (164) in our plates. The reason why this substance is called mother-of-pearl is that the true pearls are produced from its surface. They arise principally from accident or disease, and are sometimes artificially produced by pricking through the outside of the shell while the animal is living. The animal is allowed to live until it has formed a pearl over the wounded part.

MOULINSIA. Grateloup. PUPINA, Vignard. A genus of small land shells with enamelled surface and spiral operculum. See PUPINA.

MOURETIA. Gray. "Gadin," Adanson. A genus of patelliform shells, described as differing from SIPHONARIA (the original Mouretia of Adanson) in the situation of the siphon, which in Mouretia is close to the place where the muscular impression is interrupted to leave a space for the head; while in Siphonaria it is nearly half way between the anterior and posterior ends of the shell.

MOUTH. The aperture or opening of univalve shells.