Part 45

LYMNEUS. Lam. See LIMNEANA.

LYONSIA. Turt. Inequivalve species of ANATINA, Auct. which have no spoon-shaped cavity in the hinge, but an accessary piece. L. striata, fig. 491, 2.

LYRODON. Goldf. TRIGONIA?

MACLURITES. Lesuour. Journ. des Scienc. Nat. Philad. t. 1. p. 312. pl. 13. fig. 2, 3.

MACOMA. Leach. VENUS tenuis, Bl. and similar species, described as "Clothed with an epidermis; striated, compressed, oval; the summits not very prominent; two bifid teeth upon the right valve and a single undivided one upon the left."

MACRODITUS. Montf. LENTICULINA, Bl. A genus of microscopic Foraminifera.

MACROSPIRA. Guild. A genus composed of HELIX octona, Auct. Macrospira aperta, Guild.

MACROSTOMATA. Lam. ([Greek: Makros], macros, long; [Greek: stoma], stoma, mouth.) A family belonging to the first section of the order Trachelipoda, the shells belonging to which are described as haliotoid or ear shaped, with a very large aperture, destitute of an operculum. This family contains the following genera, which maybe thus distinguished.

1. VELUTINA. Globose, with velvety epidermis. Fig. 337.

2. STOMATIA. Ear-shaped; pearly within; including STOMATELLA. Fig. 335, 336.

3. SIGARETUS. The same, not pearly; including Cryptostoma. Fig. 334.

4. CORIOCELLA. The same, thin, transparent.

5. HALIOTIS. The same, not thin, nor transparent; with holes; including Padollus. Fig. 338, 339.

6. SCISSURELLA. Heliciform, with a slit near the aperture. Fig. 340.

7. PLEUROTOMARIA. Trochiform, with a slit at the edge of the aperture. Fig. 341.

MACTRA. Auct. (Mactra, a kneading trough.) Fam. Mactracea, Lam. Conchacea, Bl.--Descr. Usually thin, equivalve, sub-equilateral, sub-trigonal, slightly gaping at the extremities; hinge with one cardinal tooth, divided into two parts, diverging from the umbo, with sometimes a very small laminar tooth close to its side; a deep triangular pit near the centre, containing the cartilage; one long, lateral tooth on each side of the umbo in one valve, received between two in the other; muscular impressions two, lateral; palleal impression with a small sinus.--Obs. This genus contains many species of beautiful shells found in various parts of the world, some are common in Britain. Fossil species are not numerous, they occur in the tertiary strata. Fig. 79 to 82.

MACTRACEA. Lam. A family of the order Conchifera Dimyaria, Lam. Sect. Tenuipedes. The cartilage placed in a trigonal pit with a small external ligament. The genera may be thus distinguished.

1. LUTRARIA. No lateral teeth, shell gaping. The short species constitute the genus Ligula. Fig. 77, 78.

2. MACTRA. Lateral teeth, shell closed. This genus has been divided into Mactra, Mulinia, Schizodesma and Spisula, by Mr. Gray. Fig. 79 to 82.

3. GNATHODON. Teeth serrated, thick, one angular. Fig. 83.

4. CRASSATELLA. Shell thick, lateral teeth. Fig. 84.

5. AMPHIDESMA. A distinct external ligament, internal ligament oblique. Fig. 85.

6. ERYCINA. A short tooth on each side of the cartilaginous pit in each valve. Including Mesodesma. Fig. 86.

7. UNGULINA. Ligament flat, divided. Fig. 88.

MACULATED. (From Macula, a spot.) Spotted or patched. This term is applied by conchological writers, to those shells which are coloured in spots or small patches. In the same sense it is also used as a specific name. As for instance, Cytherea maculata, fig. 167, c. and Hippopus maculatus, fig. 156.

MAGAS. Sow. ([Greek: Magas], magas, a board, a deck.) Fam. Brachiopoda, Lam.--Descr. Equilateral, inequivalve; one valve convex, with a triangular area, divided by an angular sinus in the centre; the other valve flat, with a straight hinge line and two small projections; a partial longitudinal septum, with appendages attached to the hinge within. Differing from Terebratula in having a triangular disc, and not a circular perforation. Magas pumilus, fig. 299. Fossil in chalk.

MAGILUS. Montf. Fam. Cricostomata, Bl. Serpulacea, Lam.--Descr. Thick, tubular, irregular, contorted; rounded above, keeled beneath, free; apicial extremity convolute, heliciform, ovate or sub-globose; aperture elliptical.--Obs. This shell when in a young state presents the characteristics of a regularly formed spiral univalve, living in holes in madrepores. As the madrepore increases in bulk, the animal gives an eccentric course to the shell, in order to have its aperture even with the surface, and leaving the nucleus or young shell behind, fills it up with calcareous matter to reside in the open extremity of the tube. Fig. 9, 10. Red Sea and Mauritius.

MALACOTA. Schum. OTION. Leach.