Chapter 7

1.Cryptella. Spire mammillated; a septum. Fig. 256.2.Parmacella. Flat, haliotoid, spiral. Fig. 257, 258.3.Testacellus. Sub-spiral. Fig. 261.4.Limax. Incomplete. Fig. 259.5.Plectrophorus. Conical. Fig. 260.6.Vitrina. Heliciform, hyaline. Fig. 262, 263.

1.Cryptella. Spire mammillated; a septum. Fig. 256.

2.Parmacella. Flat, haliotoid, spiral. Fig. 257, 258.

3.Testacellus. Sub-spiral. Fig. 261.

4.Limax. Incomplete. Fig. 259.

5.Plectrophorus. Conical. Fig. 260.

6.Vitrina. Heliciform, hyaline. Fig. 262, 263.

LIMACINEA. Bl. The third family of the order Pulmobranchiata, Bl. Described as containing shells very variable in form, most frequently inclining to globular or oval; the apex always obtuse; aperture variable, but never emarginated. All the Limacinea are phytophagous and terrestrial. This family answers to the genus Helix of Linnæus and to the Colimacea of Lamarck, leaving out the Auriculacea. It contains the genera Succinea, Bulinus, Achatina, Clausilia, Pupa, Partula, Helix, Vitrina, Testacella, Limacella, Limax.LIMAX.Lam.Limacinea, Lam. and Bl.—Descr.Internal irregular, sub-quadrate, scutiform, crystalline; apex rounded, indistinct; epidermis, light brown, thin, extending beyond the margin.—Obs.The shell is placed under the scutellum of the common garden slug. Fig. 25, L. Antiquorum.LIMNACEA. Bl. The first family of the order Pulmobranchiata, Bl. The shells of this family are described as thin, with the outer lip always sharp. It contains the genera Limnea, Physa, Planorbis.LIMNEANA. Lam. A family of the order Trachelipoda, Lam. containing the following genera:—

LIMAX.Lam.Limacinea, Lam. and Bl.—Descr.Internal irregular, sub-quadrate, scutiform, crystalline; apex rounded, indistinct; epidermis, light brown, thin, extending beyond the margin.—Obs.The shell is placed under the scutellum of the common garden slug. Fig. 25, L. Antiquorum.

LIMNACEA. Bl. The first family of the order Pulmobranchiata, Bl. The shells of this family are described as thin, with the outer lip always sharp. It contains the genera Limnea, Physa, Planorbis.

LIMNEANA. Lam. A family of the order Trachelipoda, Lam. containing the following genera:—

1.Limnæa. Spire produced; includingPhysa. Fig. 308 to 310.2.Planorbis. Spire orbicular; includingPlanaria. Fig. 311, 312.

1.Limnæa. Spire produced; includingPhysa. Fig. 308 to 310.

2.Planorbis. Spire orbicular; includingPlanaria. Fig. 311, 312.

LIMNEA. Lam. (Λιμνας,limnas, lacustrine.)Fam.Limnacea, Lam. and Bl.—Descr.Oblong, light, thin; spire variable in length, acute; last whorl large, aperture large, longitudinal, entire; inner lip spread over a portion of the last whorl; columella forming an oblique fold; outer lip rounded at each extremity, thin.—Obs.These light horn-coloured shells are common in standing pools, ponds and ditches, in various parts of Europe. They resemble the Amber shell (Succinea) in shape, but the animal of the latter is amphibious, and the shell of a bright amber colour. L. Stagnalis, fig. 308. L. auricularia, fig. 309. (Radix, Montf.) The reversed species have been separated under the name Physa, fig. 310. Other generic names have been given to other species.LINES OF GROWTH. The concentric striæ or lines formed by the edges of the successive layers of shelly matter deposited by the animal by which it increases the shell. The outer edge of the aperture is always the last line of growth.LINGUIFORM. (Lingua, tongue;forma, form.) Tongue-shaped.LINGULA. Lam. (Dim. fromlingua, tongue.)Fam.Brachiopoda, Lam. Palliobranchiata, Bl.—Descr.Equivalve, oblong, depressed, thin, equilateral, gaping and pointed at the umbones, gaping and truncate or trilobate at the opposite extremities, attached by a fleshy pedicule fixed to the umbones.—Obs.This is the only bivalve shell which is pedunculated, in which respect it constitutes a singular anomaly. The ancient writers, seeing the valves separate, placed it in their systems under the name Patella Unguis. There are several recent species found in the Moluccas, and some fossils in sandy indurated marl, and in alluvium of Suffolk. L. Anatina, fig. 219, is so named from its resemblance to a duck's bill.LINGULINA. D'Orb. A genus of microscopic Foraminifera.LINTHURIS. Montf. Conch. Syst. 2. 154. A genus of microscopic Foraminifera.LIP. SeeLabiumandLabrum.LIPPISTES. Montf. A genus of microscopic Foraminifera.LITHODOMUS. Cuv. (Λιθος,lithos, stone;Δωμα,doma, house.)Fam.Mytilacea, Lam.—Descr.Transverse, elongated, cylindrical, equivalve, with the extremities rounded, and the posterior extremity rostrated; umbones not prominent, terminal; hinge straight, destitute of teeth; ligament linear, most conspicuous within; muscular impressions two.—Obs.The shells composing this genus differ from Modiola, not only in the cylindrical form, but also in the circumstance from which the generic name is derived, i. e. of their living in stones. Thus, while the form and structure of the shell bring it near the Mytili or Muscle shells, the habits of the animal cause it to approach the Lithophagi, or rock-eating molluscs of Lamarck. L. Dactylus (fig. 161,) is the Mytilus Lithophagus of ancient authors.LITHOLEPAS. Bl. (Λιθος,lithos, stone,λεπας,lepas, rock.) De Blainville's name forLithotrya, Sow.LITHOPHAGIDÆ. Lam. (Λιθος,lithos, stone;Φαγω,phago, eat or gnaw.) A family of the Conchifera Dimyaria, Lam. consisting of terebrating bivalves, gaping anteriorly, having no accessary valves; and containing the genera Saxicava, Petricola, Venerupis, to which are added other genera enumerated in explanation of figures 91 to 97. Notwithstanding the numerous genera which have been created, I think that the most convenient arrangement will be to reduce them to two, thus—

LINES OF GROWTH. The concentric striæ or lines formed by the edges of the successive layers of shelly matter deposited by the animal by which it increases the shell. The outer edge of the aperture is always the last line of growth.

LINGUIFORM. (Lingua, tongue;forma, form.) Tongue-shaped.

LINGULA. Lam. (Dim. fromlingua, tongue.)Fam.Brachiopoda, Lam. Palliobranchiata, Bl.—Descr.Equivalve, oblong, depressed, thin, equilateral, gaping and pointed at the umbones, gaping and truncate or trilobate at the opposite extremities, attached by a fleshy pedicule fixed to the umbones.—Obs.This is the only bivalve shell which is pedunculated, in which respect it constitutes a singular anomaly. The ancient writers, seeing the valves separate, placed it in their systems under the name Patella Unguis. There are several recent species found in the Moluccas, and some fossils in sandy indurated marl, and in alluvium of Suffolk. L. Anatina, fig. 219, is so named from its resemblance to a duck's bill.

LINGULINA. D'Orb. A genus of microscopic Foraminifera.

LINTHURIS. Montf. Conch. Syst. 2. 154. A genus of microscopic Foraminifera.

LIP. SeeLabiumandLabrum.

LIPPISTES. Montf. A genus of microscopic Foraminifera.

LITHODOMUS. Cuv. (Λιθος,lithos, stone;Δωμα,doma, house.)Fam.Mytilacea, Lam.—Descr.Transverse, elongated, cylindrical, equivalve, with the extremities rounded, and the posterior extremity rostrated; umbones not prominent, terminal; hinge straight, destitute of teeth; ligament linear, most conspicuous within; muscular impressions two.—Obs.The shells composing this genus differ from Modiola, not only in the cylindrical form, but also in the circumstance from which the generic name is derived, i. e. of their living in stones. Thus, while the form and structure of the shell bring it near the Mytili or Muscle shells, the habits of the animal cause it to approach the Lithophagi, or rock-eating molluscs of Lamarck. L. Dactylus (fig. 161,) is the Mytilus Lithophagus of ancient authors.

LITHOLEPAS. Bl. (Λιθος,lithos, stone,λεπας,lepas, rock.) De Blainville's name forLithotrya, Sow.

LITHOPHAGIDÆ. Lam. (Λιθος,lithos, stone;Φαγω,phago, eat or gnaw.) A family of the Conchifera Dimyaria, Lam. consisting of terebrating bivalves, gaping anteriorly, having no accessary valves; and containing the genera Saxicava, Petricola, Venerupis, to which are added other genera enumerated in explanation of figures 91 to 97. Notwithstanding the numerous genera which have been created, I think that the most convenient arrangement will be to reduce them to two, thus—

1.Petricola, with distinct cardinal teeth, including, Clothe, Venerirupis and Coralliophaga. Fig. 91, 92, 97.2.Saxicava, without teeth, including Biapholius, Hiatella, Sphænia, Byssomya, and Thracia. Fig. 93 to 96.

1.Petricola, with distinct cardinal teeth, including, Clothe, Venerirupis and Coralliophaga. Fig. 91, 92, 97.

2.Saxicava, without teeth, including Biapholius, Hiatella, Sphænia, Byssomya, and Thracia. Fig. 93 to 96.

LITHOTRYA. G. B. Sowerby. (Λιθος,lithos, stone;τρυο,truo, to bore through.)Fam.Pedunculated Cirripedes, Lam.—Descr.Eight unequal valves, forming a laterally compressed cone, the lower central valves being very minute; pedicle fleshy, scaly at the upper extremity; fixed at the base in a patelliform shelly support.—Obs.This genus derives its name from the power possessed by the animal of making dwelling holes in stones or pieces of rock. The remarkable shelly cups at the base of the pedicle is regarded as analogous to the shelly base of the Balanus, so that this genus would form an intermediate link between the Sessile and Pedunculated Cirripedes of Lamarck. Fig. 39, L. dorsalis. West India Islands.LITIOPA. Ranz.Fam.Turbinacea, Lam.—Descr."Shell not very thick, horny, with a slight epidermis, rather transparent, conical, with whorls somewhat rounded; the last being larger than all the rest together; with the apex pointed, longitudinally grooved; aperture oval, larger anteriorly than posteriorly, with the lips disunited, the right lip simple, separated from the left by a rather indistinct notch, or a slight emargination in the contour. The left lip slightly reflected backwards, so as to form a kind of salient margin with the anterior extremity of the columella, which is united, rounded, arcuated and slightly truncated at the anterior."—Obs.The Molluscous animals, whose shells are thus described, are found in the Mediterranean, and are remarkable for the power of suspending themselves from the sea-weed on which they live, by a thread resembling a spider's web. The general appearance of the shell presents a medium between Phasianella and Littorina, but it is apparently destitute of an operculum.LITTORINA. Fer. (Littus, the sea-shore.)Fam.Turbinacea, Lam.—Descr.Turbinated, thick; spire acuminated, consisting of few whorls, about one third of the axis in length; aperture entire, large, rounded anteriorly; outer lip thickened within, acute; columella rather flattened; operculum horny, spiral, with rapidly increasing volutions.—Obs.The shells composing this genus are known from Turbo and Phasianella by the horny operculum; and from Trochus, which has also a horny operculum, by the small number of the whorls. The Littorinæ, among which may be enumerated the common Periwinkle, are, as the name implies, found on sea shores, feeding upon seaweed, in all parts of the world. Fig. 363,L. Vulgaris.LITUACEA. Bl. The second family of Polythalamacea. Bl. The shells are described as chambered, symmetrical, convolute in part of their extent, but constantly straight towards the termination. The genus Spirula, which is admitted into this family, does not properly belong to it, any more than to the Lituolæ of Lamarck, in which it is also placed. It does not agree with the descriptions of either. This family partly corresponds with the "Lituolées," Lam. and contains the genera Lituola, Ichthyosarcolites, Spirula, Hamites and Ammonoceras.LITUACEA. Lam. A family of the order Polythalamous Cephalopoda, Lam. containing the genus Spirula, fig. 471.LITUITUS. Montf.Spirolina, Lam. Microscopic.LITUOLA. Lam. A genus of microscopic Foraminifera.LITUOLÆ. Lam. The third family of Polythalamous Cephalopoda, Lam. the shells of which are described as partially spiral, the last whorl continuing in a straight line. The transverse septa which divide the chambers, are in general pierced by a siphon which breaks itself off before it reaches the succeeding septum. This family contains the genera of microscopic Foraminifera Lituola and Spirolina. The genus Spirula, also placed in this family, does not by any means agree with Lamarck's definitions "the last whorl continuing in a straight line."LITUUS. Humph.Cyclostoma?Lam.LIVID. (Fromlividus.) Of a pale, dull, blue colour. The adjective is sometimes used as a specific name.Ex.Conuslividus, Sanguinolarialivida.LOBARIA. Schum.Sanguinolariarosea, Lam. (fig. 98) and other similar species.LOBATE or LOBED. Divided into parts.LOBATULA. Fleming. A genus composed of two very minute species of chambered shells. Serpula lobata and S. concamerata, Mont. Test. Brit. 515.LOMASTOMA. Rafinesque. An imperfectly defined genus, probably belonging to the Limnacea.LONGITUDINAL. Lengthwise. Longitudinal striæ, ribs, &c. are those which radiate from the apex and follow the spiral direction of the whorls, in spiral shells; and from the umbo to the ventral margin in bivalves. The term "decourantes" is employed by French conchologists. The bands in Achatina, fig. 286, are longitudinal or spiral.LORIPEDES. Poli. A genus composed of species ofLucina, Auct. in which the lunules are not prominent.LOTORIUM. Montf. A genus composed of species ofTriton, Auct. in which the aperture is effuse. T. Lotorium, fig. 400.LOTTIA. Gray.Patelloida, Quoy and Gaimard.LUCERNA. Humph. A generic name applied to some species of Helix included in De Ferussac's sub-genus Helicogena.LUCERNELLA. Sw. A genus of "Lucerninæ," Sw. thus described: "Teeth on both sides of the aperture; surface regularly and distinctly striated. Circumference convex."LUCIDULA. Sw. A sub-genus of Lucerna, Humph. thus described: "Aperture transverse, both lips much thickened and united; the outer with marginal obsolete teeth at the base; umbilicus closed. Barbadensis,Lam.No. 49. p. 78. Fêr. Moll. pl. 47, 2, 3, 4."LUCINA. Brug.Fam.Nymphacea, Lam. Conchacea, Bl.—Descr.Equivalve, inequilateral, orbicular, lenticular, radiately striated; hinge with, generally, two minute cardinal teeth, which are sometimes nearly obsolete, and two lateral teeth, on each side of the umbo in one valve, one in the other; ligament external, partly hidden by the margins of the valves when closed. Muscular impressions two in each valve, the anterior one produced into an elongated, ligulate band, the posterior short and semi-rotund; impression of the mantle not sinuated.—Obs.The shells of this genus resemble Amphidesma in general form, but are distinguished by the external ligament, the elongated muscular impression, and the want of a sinus in the palleal impression. East and West Indies, and European shores. Fig. 104, L. Tigerina.LUNULATE. (Luna, the moon, dim.) Moon-shaped, having the form of a crescent. Applied most frequently to muscular impressions. Semilunar is sometimes used, perhaps with greater accuracy, to express the same shape.LUNULE. An impression on the anterior dorsal margin of some bivalve shells. The similar impression on the posterior dorsal margin is called theescutcheon.LUPONIA. Gray. A genus composed of species ofCypræa, Auct. which are described as having the anterior of the columellar lip crossed by several irregular ridges, without any distinct marginal ones, internally narrow, flat; the shell pear-shaped, smooth, or cross-ribbed.Ex.C. Algoensis, Luponia Algoensis, Gray, fig. 447.LUTRARIA. Auct. (Lutum?mud.)—Fam.Mactracea, Lam.—Descr.Thin, equivalve, inequilateral, transverse, oblong or ovate, gaping at both extremities; hinge with one double and sometimes one single cardinal tooth in each valve, and a triangular, oblique pit with a prominent margin, containing the ligament; muscular impressions distant; palleal impression having a large sinus.—Obs.This genus differs from Mactra in the entire absence or indistinctness of lateral teeth. Fig. 77, L. Papyracea. (Ligula, Leach.) Fig. 78. L. Solenoides. Sandy and muddy shores.LUTRICOLA. Bl.Lutraria. Lam. Fig. 77, 78.LYCOPHRIS. Montf. A microscopic fossil described as resemblingNummulites, but having a granulated surface.LYMNADEA. Sw. A sub-genus of "Mysca," Turton, in the family of Nayades, Lam. thus described: "Posterior hinge margin elevated and winged; the valves connate; the surface smooth. L. alata.Sw.Ex.Conch. (fig. 48.) fragilis.Sw.Zool. Ill. compressa,Lea.Am. Tr. iii. pl. 12. f. 22." Sw. p. 379.LYMNEA. SeeLimnea.LYMNEUS. Lam. SeeLimneana.LYONSIA. Turt. Inequivalve species ofAnatina, 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.Venustenuis, 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 ofHelixoctona, Auct. Macrospira aperta, Guild.MACROSTOMATA. Lam. (Μακρος,macros, long;στομα,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.

LITIOPA. Ranz.Fam.Turbinacea, Lam.—Descr."Shell not very thick, horny, with a slight epidermis, rather transparent, conical, with whorls somewhat rounded; the last being larger than all the rest together; with the apex pointed, longitudinally grooved; aperture oval, larger anteriorly than posteriorly, with the lips disunited, the right lip simple, separated from the left by a rather indistinct notch, or a slight emargination in the contour. The left lip slightly reflected backwards, so as to form a kind of salient margin with the anterior extremity of the columella, which is united, rounded, arcuated and slightly truncated at the anterior."—Obs.The Molluscous animals, whose shells are thus described, are found in the Mediterranean, and are remarkable for the power of suspending themselves from the sea-weed on which they live, by a thread resembling a spider's web. The general appearance of the shell presents a medium between Phasianella and Littorina, but it is apparently destitute of an operculum.

LITTORINA. Fer. (Littus, the sea-shore.)Fam.Turbinacea, Lam.—Descr.Turbinated, thick; spire acuminated, consisting of few whorls, about one third of the axis in length; aperture entire, large, rounded anteriorly; outer lip thickened within, acute; columella rather flattened; operculum horny, spiral, with rapidly increasing volutions.—Obs.The shells composing this genus are known from Turbo and Phasianella by the horny operculum; and from Trochus, which has also a horny operculum, by the small number of the whorls. The Littorinæ, among which may be enumerated the common Periwinkle, are, as the name implies, found on sea shores, feeding upon seaweed, in all parts of the world. Fig. 363,L. Vulgaris.

LITUACEA. Bl. The second family of Polythalamacea. Bl. The shells are described as chambered, symmetrical, convolute in part of their extent, but constantly straight towards the termination. The genus Spirula, which is admitted into this family, does not properly belong to it, any more than to the Lituolæ of Lamarck, in which it is also placed. It does not agree with the descriptions of either. This family partly corresponds with the "Lituolées," Lam. and contains the genera Lituola, Ichthyosarcolites, Spirula, Hamites and Ammonoceras.

LITUACEA. Lam. A family of the order Polythalamous Cephalopoda, Lam. containing the genus Spirula, fig. 471.

LITUITUS. Montf.Spirolina, Lam. Microscopic.

LITUOLA. Lam. A genus of microscopic Foraminifera.

LITUOLÆ. Lam. The third family of Polythalamous Cephalopoda, Lam. the shells of which are described as partially spiral, the last whorl continuing in a straight line. The transverse septa which divide the chambers, are in general pierced by a siphon which breaks itself off before it reaches the succeeding septum. This family contains the genera of microscopic Foraminifera Lituola and Spirolina. The genus Spirula, also placed in this family, does not by any means agree with Lamarck's definitions "the last whorl continuing in a straight line."

LITUUS. Humph.Cyclostoma?Lam.

LIVID. (Fromlividus.) Of a pale, dull, blue colour. The adjective is sometimes used as a specific name.Ex.Conuslividus, Sanguinolarialivida.

LOBARIA. Schum.Sanguinolariarosea, Lam. (fig. 98) and other similar species.

LOBATE or LOBED. Divided into parts.

LOBATULA. Fleming. A genus composed of two very minute species of chambered shells. Serpula lobata and S. concamerata, Mont. Test. Brit. 515.

LOMASTOMA. Rafinesque. An imperfectly defined genus, probably belonging to the Limnacea.

LONGITUDINAL. Lengthwise. Longitudinal striæ, ribs, &c. are those which radiate from the apex and follow the spiral direction of the whorls, in spiral shells; and from the umbo to the ventral margin in bivalves. The term "decourantes" is employed by French conchologists. The bands in Achatina, fig. 286, are longitudinal or spiral.

LORIPEDES. Poli. A genus composed of species ofLucina, Auct. in which the lunules are not prominent.

LOTORIUM. Montf. A genus composed of species ofTriton, Auct. in which the aperture is effuse. T. Lotorium, fig. 400.

LOTTIA. Gray.Patelloida, Quoy and Gaimard.

LUCERNA. Humph. A generic name applied to some species of Helix included in De Ferussac's sub-genus Helicogena.

LUCERNELLA. Sw. A genus of "Lucerninæ," Sw. thus described: "Teeth on both sides of the aperture; surface regularly and distinctly striated. Circumference convex."

LUCIDULA. Sw. A sub-genus of Lucerna, Humph. thus described: "Aperture transverse, both lips much thickened and united; the outer with marginal obsolete teeth at the base; umbilicus closed. Barbadensis,Lam.No. 49. p. 78. Fêr. Moll. pl. 47, 2, 3, 4."

LUCINA. Brug.Fam.Nymphacea, Lam. Conchacea, Bl.—Descr.Equivalve, inequilateral, orbicular, lenticular, radiately striated; hinge with, generally, two minute cardinal teeth, which are sometimes nearly obsolete, and two lateral teeth, on each side of the umbo in one valve, one in the other; ligament external, partly hidden by the margins of the valves when closed. Muscular impressions two in each valve, the anterior one produced into an elongated, ligulate band, the posterior short and semi-rotund; impression of the mantle not sinuated.—Obs.The shells of this genus resemble Amphidesma in general form, but are distinguished by the external ligament, the elongated muscular impression, and the want of a sinus in the palleal impression. East and West Indies, and European shores. Fig. 104, L. Tigerina.

LUNULATE. (Luna, the moon, dim.) Moon-shaped, having the form of a crescent. Applied most frequently to muscular impressions. Semilunar is sometimes used, perhaps with greater accuracy, to express the same shape.

LUNULE. An impression on the anterior dorsal margin of some bivalve shells. The similar impression on the posterior dorsal margin is called theescutcheon.

LUPONIA. Gray. A genus composed of species ofCypræa, Auct. which are described as having the anterior of the columellar lip crossed by several irregular ridges, without any distinct marginal ones, internally narrow, flat; the shell pear-shaped, smooth, or cross-ribbed.Ex.C. Algoensis, Luponia Algoensis, Gray, fig. 447.

LUTRARIA. Auct. (Lutum?mud.)—Fam.Mactracea, Lam.—Descr.Thin, equivalve, inequilateral, transverse, oblong or ovate, gaping at both extremities; hinge with one double and sometimes one single cardinal tooth in each valve, and a triangular, oblique pit with a prominent margin, containing the ligament; muscular impressions distant; palleal impression having a large sinus.—Obs.This genus differs from Mactra in the entire absence or indistinctness of lateral teeth. Fig. 77, L. Papyracea. (Ligula, Leach.) Fig. 78. L. Solenoides. Sandy and muddy shores.

LUTRICOLA. Bl.Lutraria. Lam. Fig. 77, 78.

LYCOPHRIS. Montf. A microscopic fossil described as resemblingNummulites, but having a granulated surface.

LYMNADEA. Sw. A sub-genus of "Mysca," Turton, in the family of Nayades, Lam. thus described: "Posterior hinge margin elevated and winged; the valves connate; the surface smooth. L. alata.Sw.Ex.Conch. (fig. 48.) fragilis.Sw.Zool. Ill. compressa,Lea.Am. Tr. iii. pl. 12. f. 22." Sw. p. 379.

LYMNEA. SeeLimnea.

LYMNEUS. Lam. SeeLimneana.

LYONSIA. Turt. Inequivalve species ofAnatina, 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.Venustenuis, 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 ofHelixoctona, Auct. Macrospira aperta, Guild.

MACROSTOMATA. Lam. (Μακρος,macros, long;στομα,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; includingStomatella. Fig. 335, 336.3.Sigaretus.The same, not pearly; includingCryptostoma. Fig. 334.4.Coriocella.The same, thin, transparent.5.Haliotis.The same, not thin, nor transparent; with holes; includingPadollus. 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.

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

2.Stomatia.Ear-shaped; pearly within; includingStomatella. Fig. 335, 336.

3.Sigaretus.The same, not pearly; includingCryptostoma. Fig. 334.

4.Coriocella.The same, thin, transparent.

5.Haliotis.The same, not thin, nor transparent; with holes; includingPadollus. 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.

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 genusLigula. 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.

1.Lutraria.No lateral teeth, shell gaping. The short species constitute the genusLigula. 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. (FromMacula, 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. (Μαγας,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.MALACOZOA. Bl. (Μαλακος,malacos, soft;Ζωον,zoon, animal.) The type or general appellative in De Blainville's system, including all molluscous animals, excepting those with multivalve shells.MALDANIA. Lam. The second family of the order Annelides Sedentaria. The only genus of shells described in this family is Dentalium, fig. 2, to which may be added Pharetrium, König. fig. 3. It is doubtful however whether the latter do not belong to an unknown genus of Pteropodous Mollusca.MALEA. Valenciennes. A genus composed ofDoliumlatilabrum, Kiener, and other similar species.MALENTOZOA. Bl. (Μαλακος,malacos, soft;εν,in,τεμνω,temno, cut;Ζωον,zoon, animal.) Or articulated mollusca. The sub-type in De Blainville's system, comprehending those with multivalve shells.MALLEACEA. Lam. A family belonging to the order of Conchifera Monomyaria. Containing the following genera of irregular pearly bivalves.

MAGAS. Sow. (Μαγας,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.

MALACOZOA. Bl. (Μαλακος,malacos, soft;Ζωον,zoon, animal.) The type or general appellative in De Blainville's system, including all molluscous animals, excepting those with multivalve shells.

MALDANIA. Lam. The second family of the order Annelides Sedentaria. The only genus of shells described in this family is Dentalium, fig. 2, to which may be added Pharetrium, König. fig. 3. It is doubtful however whether the latter do not belong to an unknown genus of Pteropodous Mollusca.

MALEA. Valenciennes. A genus composed ofDoliumlatilabrum, Kiener, and other similar species.

MALENTOZOA. Bl. (Μαλακος,malacos, soft;εν,in,τεμνω,temno, cut;Ζωον,zoon, animal.) Or articulated mollusca. The sub-type in De Blainville's system, comprehending those with multivalve shells.

MALLEACEA. Lam. A family belonging to the order of Conchifera Monomyaria. Containing the following genera of irregular pearly bivalves.

1.Avicula.Hinge linear, simple, includingMeleagrina. Fig. 163, 164.2.Perna.Hinge with linear grooves, includingPulvinites. Fig. 166, 170.3.Gervillia.Shaped like Modiola, with irregular grooves. Fig. 162.4.Crenatula.Hinge with a series of pits. Fig. 168.5.Catillus.Like Perna, but more regular and convex. Fig. 167.6.Malleus.A triangular disc on the hinge, and two auricles. Fig. 165.

1.Avicula.Hinge linear, simple, includingMeleagrina. Fig. 163, 164.

2.Perna.Hinge with linear grooves, includingPulvinites. Fig. 166, 170.

3.Gervillia.Shaped like Modiola, with irregular grooves. Fig. 162.

4.Crenatula.Hinge with a series of pits. Fig. 168.

5.Catillus.Like Perna, but more regular and convex. Fig. 167.

6.Malleus.A triangular disc on the hinge, and two auricles. Fig. 165.

MALLEUS. Auct. (Malleus, a hammer.)Fam.Malleacea, Lam. Margaritacea, Bl.—Descr.Equivalve, inequilateral, foliaceous, trilobate, undulated, irregular, attached by a byssus passing through a sinus in one valve; hinge rectilinear, lengthened by two auricles; with a small disc under the umbones, containing the ligament, and a groove containing the cartilage; muscular impressions one in each valve, large, uniform, and one or two others extremely minute.—Obs.Malleus Vulgaris, the type of this genus, is a most singular shell, commonly called the "Hammer Oyster," from the peculiarity of its shape. It belongs to the Linnæan genus Ostrea, from which it differs in being attached by a byssus. Fig. 165, M. Vulgaris. Tropical.MAMILLARIA. Sw. A sub-genus ofNatica, corresponding with Polinices of Montfort, having the spire small and the umbilicus filled.Ex.Natica Mamilla, Auct. fig. 327.MAMMILLATED. (Mammula, a little teat.) A term applied to the apex of a shell when it is rounded like a teat.Ex.Voluta Vespertilio, fig. 433.MARGARITA. Leach. (Margarita, a pearl.) A genus of small shells resembling the genus Trochus, from which it differs in having an operculum consisting of few whorls. M. tæniata, fig. 362. Mr. G. B. Sowerby, sen. has enumerated 15 species in a list accompanying the figures published by the author of this manual in Nos. 132 to 134 of his Conchological Illustrations.MARGARITACEA. Bl. The third family of Lamellibranchiata, Bl. The shells belonging to it are described as irregular, inequivalve, inequilateral, black or horny without, pearly within; hinge auriculated, scarcely developed, and without teeth. The ligament is variable and there is a large sub-central muscular impression. This family contains the genera Vulsella, Malleus, Pinna, Crenatula, Inoceramus, Catillus, Pulvinites, Gervillia and Avicula.MARGARITACEOUS. (Margarita, a pearl.) Pearly.MARGARITANA. Schum. A sub-genus of Uniones, composed of species having "one cardinal tooth."Alasmodon, Say.MyaMargaritifera, Linn.MARGARITIFEROUS. (Margarita, pearl;fero, to bear.) Pearl-bearing. Applied to shells which form pearls; as Meleagrina Margaritifera, or Pearl-bearing Oyster.MARGINAL. Near the margin or edge.MARGINATED. (Margo, edge.) Having an edge or border thicker than the rest of the shell, from which circumstance the little genus Marginella derives its name.MARGINELLA. (A little rim or border.)Fam.Columellaria, Lam. Angyostomata, Bl.—Descr.Ovate, smooth, shining, with a short, sometimes hidden spire; aperture narrow, emarginated; columella with several oblique folds; outer lip neatly reflected.—Obs.This genus of pretty little shells differs from Voluta, in the reflection of the outer lip. The animal covers the greater part of the shell with the mantle, and by continually depositing vitreous matter gives it a bright polish, which, together with the delicately neat arrangement of colours in most species, renders them exceedingly beautiful. The Marginellæ are marine and tropical. A few fossil species are found in the Calc-grossier. Fig. 437. M. Glabella.Glabella, Sw.MARGINULINA. D'Orb. A genus of microscopic Foraminifera.MARINE CONCHACEA. SeeConchacea.MARINE TESTACEA. Those shell-fish which inhabit seas, lakes, &c. of salt water, in distinction from theAquaticTestacea, or those which are found in rivers, ponds or stagnant pools of fresh water: and also from theLandTestacea, which live on land and breathe air. The great proportion of shells belong to the former class, those of the latter two classes being limited in their number, and in the genera to which they belong.MARINULA. King. A genus of small shells resembling Auricula and Pedipes, described as "Ovate, sub-solid, with aperture ovate entire; columella bidentate, uniplicated towards the base, with large sub-remote teeth; the largest uppermost; no operculum."MARMAROSTOMA. Sw. A genus of "Trochidæ," Sw. thus described: "Umbilicus deep; spire of few whorls, much depressed, and obtuse; inner lip obsolete; base even more produced than inSenectus, but never distinctly channeled. M. versicolor. Mont. 176. f. 1740, 1741, undulata. Chem. 169. f. 1640, 1641," Sw. p. 348.MARPESSA. Gray. A sub-genus of Clausilia, C. bidens, &c. Auct. Gray's Turton, p. 212.MARTESIA. Leach. A genus composed of those species ofPholas, Auct. which are described as short, cuneiform, nearly closed at both extremities, having several accessary pieces on the middle of the back, and two marginal, lower down.MEASUREMENT. The most approved method of stating the measurements of various kinds of shells is as follows:symmetrical convolute univalves, the length is from anterior to posterior; the depth from ventral to dorsal; the breadth, from side to side of the aperture. Ofsymmetrical conical univalves, length, from front to back; breadth from side to side; depth from apex to base. Ofspiral univalves, length, from apex to anterior of the columella or axis of the shell; breadth, across from the outer lip to the opposite side. Ofnon-symmetrical bivalves, the length is from the anterior to the posterior margin; breadth, from the greatest convexity of one valve to the corresponding part of the other; depth, from the ventral to the dorsal margin.MEGADESMA. Bowd. (Μεγας,megas, great;δεσμα,desma, ligament.)Potamophila, Sow.Galathæa, Lam.MEGADOMUS. Sw. A sub-genus of Unio, thus described: "Only one lateral tooth in each valve; cardinal teeth two; posterior hinge margin winged. M. gigas,Sw." Sw. p. 378.MEGALODON. Sow. (Μεγας,megas, great;οδος,odos, tooth.)Fam.Cardiacea, Lam.—Descr.Equivalve, longitudinal, acuminated at the umbones, thick; hinge forming an incrassated septum across the cavity of the shell, with a large bifid tooth in the right valve, and one irregular and one pointed in the left; ligament long, external.—Obs.The general form, the thickened hinge reaching across the cavity of the valve and the terminal umbones serve to distinguish this genus from Cardita, to which, however, it is nearly allied. M. cucullatus, fig. 127.MEGALOMASTOMA. Guild. A sub-genus of Cyclostoma, thus described: "Cylindrical, resemblingPupa, but has a horny operculum; spire not thickened; teeth or fold on the pillar none, flavulaSw.En. Méth. 461. f. 6, brunneaGuild.(fig. 97. g. h. 1.)" Sw. p. 336. Mr. Gray applies the name to those species which have "a groove or ridge in front of the mouth near the pillar."MEGARIMA. Rafinesque. A genus proposed to include species ofTerebratula, Auct. which are smooth and nearly equivalve. T. lævis, T. crassa, T. truncula.MEGASPIRA. Lea. (Μεγας,megas, great, and spire.) M. Ruschenbergiana, (fig. 294) is a pupiform land shell remarkable for the length of its spire, which consists of no less than twenty-five close set, narrow, gradually increasing whorls. The outer lip is simple, slightly thickened; the inner lip has a tooth on the body-whorl, and two folds on the columella. Only one species of this singular shell is known.MEGATREMA. Leach. A genus composed of those species of Pyrgoma, Auct. which have a large aperture. Fig. 33.MELACANTHA. Sw. A sub-genus of Melania. Sw. p. 341.MELAFUSUS. Sw. A sub-genus of Melanopsis. Sw. p. 341.MELAMPUS. Montf.Conovulum, Lam. A genus composed of species ofAuricula, Auct. of a conical form. A. conoidalis, fig. 298.MELANIA. Auct. (Μελας,melas, black.)Fam.Melaniens, Lam. Ellipsostomata, Bl.—Descr.Turrited; spire generally elongated, acute; aperture entire, oval or oblong, pointed at the posterior extremity, rounded anteriorly, with a kind of indistinct canal or sinuosity: epidermis thick, generally black.—Obs.In common with other fresh-water shells, the Melaniæ are frequently found with corroded apices. This genus is known from Melanopsis by the absence of the notch at the anterior part of the aperture. The Melaniæ occur in rivers of warm climates. The fossil species are frequent in upper marine formations. Fig. 313, M. subulata.MELANIANA. Lam. (Melaniens.) A family belonging to the first section of the order Trachelipoda. The genera contained in it maybe distinguished as follows.

MAMILLARIA. Sw. A sub-genus ofNatica, corresponding with Polinices of Montfort, having the spire small and the umbilicus filled.Ex.Natica Mamilla, Auct. fig. 327.

MAMMILLATED. (Mammula, a little teat.) A term applied to the apex of a shell when it is rounded like a teat.Ex.Voluta Vespertilio, fig. 433.

MARGARITA. Leach. (Margarita, a pearl.) A genus of small shells resembling the genus Trochus, from which it differs in having an operculum consisting of few whorls. M. tæniata, fig. 362. Mr. G. B. Sowerby, sen. has enumerated 15 species in a list accompanying the figures published by the author of this manual in Nos. 132 to 134 of his Conchological Illustrations.

MARGARITACEA. Bl. The third family of Lamellibranchiata, Bl. The shells belonging to it are described as irregular, inequivalve, inequilateral, black or horny without, pearly within; hinge auriculated, scarcely developed, and without teeth. The ligament is variable and there is a large sub-central muscular impression. This family contains the genera Vulsella, Malleus, Pinna, Crenatula, Inoceramus, Catillus, Pulvinites, Gervillia and Avicula.

MARGARITACEOUS. (Margarita, a pearl.) Pearly.

MARGARITANA. Schum. A sub-genus of Uniones, composed of species having "one cardinal tooth."Alasmodon, Say.MyaMargaritifera, Linn.

MARGARITIFEROUS. (Margarita, pearl;fero, to bear.) Pearl-bearing. Applied to shells which form pearls; as Meleagrina Margaritifera, or Pearl-bearing Oyster.

MARGINAL. Near the margin or edge.

MARGINATED. (Margo, edge.) Having an edge or border thicker than the rest of the shell, from which circumstance the little genus Marginella derives its name.

MARGINELLA. (A little rim or border.)Fam.Columellaria, Lam. Angyostomata, Bl.—Descr.Ovate, smooth, shining, with a short, sometimes hidden spire; aperture narrow, emarginated; columella with several oblique folds; outer lip neatly reflected.—Obs.This genus of pretty little shells differs from Voluta, in the reflection of the outer lip. The animal covers the greater part of the shell with the mantle, and by continually depositing vitreous matter gives it a bright polish, which, together with the delicately neat arrangement of colours in most species, renders them exceedingly beautiful. The Marginellæ are marine and tropical. A few fossil species are found in the Calc-grossier. Fig. 437. M. Glabella.Glabella, Sw.

MARGINULINA. D'Orb. A genus of microscopic Foraminifera.

MARINE CONCHACEA. SeeConchacea.

MARINE TESTACEA. Those shell-fish which inhabit seas, lakes, &c. of salt water, in distinction from theAquaticTestacea, or those which are found in rivers, ponds or stagnant pools of fresh water: and also from theLandTestacea, which live on land and breathe air. The great proportion of shells belong to the former class, those of the latter two classes being limited in their number, and in the genera to which they belong.

MARINULA. King. A genus of small shells resembling Auricula and Pedipes, described as "Ovate, sub-solid, with aperture ovate entire; columella bidentate, uniplicated towards the base, with large sub-remote teeth; the largest uppermost; no operculum."

MARMAROSTOMA. Sw. A genus of "Trochidæ," Sw. thus described: "Umbilicus deep; spire of few whorls, much depressed, and obtuse; inner lip obsolete; base even more produced than inSenectus, but never distinctly channeled. M. versicolor. Mont. 176. f. 1740, 1741, undulata. Chem. 169. f. 1640, 1641," Sw. p. 348.

MARPESSA. Gray. A sub-genus of Clausilia, C. bidens, &c. Auct. Gray's Turton, p. 212.

MARTESIA. Leach. A genus composed of those species ofPholas, Auct. which are described as short, cuneiform, nearly closed at both extremities, having several accessary pieces on the middle of the back, and two marginal, lower down.

MEASUREMENT. The most approved method of stating the measurements of various kinds of shells is as follows:symmetrical convolute univalves, the length is from anterior to posterior; the depth from ventral to dorsal; the breadth, from side to side of the aperture. Ofsymmetrical conical univalves, length, from front to back; breadth from side to side; depth from apex to base. Ofspiral univalves, length, from apex to anterior of the columella or axis of the shell; breadth, across from the outer lip to the opposite side. Ofnon-symmetrical bivalves, the length is from the anterior to the posterior margin; breadth, from the greatest convexity of one valve to the corresponding part of the other; depth, from the ventral to the dorsal margin.

MEGADESMA. Bowd. (Μεγας,megas, great;δεσμα,desma, ligament.)Potamophila, Sow.Galathæa, Lam.

MEGADOMUS. Sw. A sub-genus of Unio, thus described: "Only one lateral tooth in each valve; cardinal teeth two; posterior hinge margin winged. M. gigas,Sw." Sw. p. 378.

MEGALODON. Sow. (Μεγας,megas, great;οδος,odos, tooth.)Fam.Cardiacea, Lam.—Descr.Equivalve, longitudinal, acuminated at the umbones, thick; hinge forming an incrassated septum across the cavity of the shell, with a large bifid tooth in the right valve, and one irregular and one pointed in the left; ligament long, external.—Obs.The general form, the thickened hinge reaching across the cavity of the valve and the terminal umbones serve to distinguish this genus from Cardita, to which, however, it is nearly allied. M. cucullatus, fig. 127.

MEGALOMASTOMA. Guild. A sub-genus of Cyclostoma, thus described: "Cylindrical, resemblingPupa, but has a horny operculum; spire not thickened; teeth or fold on the pillar none, flavulaSw.En. Méth. 461. f. 6, brunneaGuild.(fig. 97. g. h. 1.)" Sw. p. 336. Mr. Gray applies the name to those species which have "a groove or ridge in front of the mouth near the pillar."

MEGARIMA. Rafinesque. A genus proposed to include species ofTerebratula, Auct. which are smooth and nearly equivalve. T. lævis, T. crassa, T. truncula.

MEGASPIRA. Lea. (Μεγας,megas, great, and spire.) M. Ruschenbergiana, (fig. 294) is a pupiform land shell remarkable for the length of its spire, which consists of no less than twenty-five close set, narrow, gradually increasing whorls. The outer lip is simple, slightly thickened; the inner lip has a tooth on the body-whorl, and two folds on the columella. Only one species of this singular shell is known.

MEGATREMA. Leach. A genus composed of those species of Pyrgoma, Auct. which have a large aperture. Fig. 33.

MELACANTHA. Sw. A sub-genus of Melania. Sw. p. 341.

MELAFUSUS. Sw. A sub-genus of Melanopsis. Sw. p. 341.

MELAMPUS. Montf.Conovulum, Lam. A genus composed of species ofAuricula, Auct. of a conical form. A. conoidalis, fig. 298.

MELANIA. Auct. (Μελας,melas, black.)Fam.Melaniens, Lam. Ellipsostomata, Bl.—Descr.Turrited; spire generally elongated, acute; aperture entire, oval or oblong, pointed at the posterior extremity, rounded anteriorly, with a kind of indistinct canal or sinuosity: epidermis thick, generally black.—Obs.In common with other fresh-water shells, the Melaniæ are frequently found with corroded apices. This genus is known from Melanopsis by the absence of the notch at the anterior part of the aperture. The Melaniæ occur in rivers of warm climates. The fossil species are frequent in upper marine formations. Fig. 313, M. subulata.

MELANIANA. Lam. (Melaniens.) A family belonging to the first section of the order Trachelipoda. The genera contained in it maybe distinguished as follows.

1.Melanopsis. Aperture notched; columellar lip thickened above; includingPirena. Fig. 315, 316.2.Melania. Aperture not notched; columellar lip not thickened; includingAuculosa,Pasithæa,Io. Fig. 313, 314, 317.

1.Melanopsis. Aperture notched; columellar lip thickened above; includingPirena. Fig. 315, 316.

2.Melania. Aperture not notched; columellar lip not thickened; includingAuculosa,Pasithæa,Io. Fig. 313, 314, 317.

MELANITHES. Sw. A sub-genus of Melanopsis. Sw. p. 341.MELANOIDES. Olivier.Melanopsis.Fer.MELANOPSIS. Fer.Fam.Melaniana, Lam. Entomostomata, Bl.—Descr.Oval or oblong, fusiform; spire acute, sometimes elongated; aperture oblong or oval, pyriform, with a distinct notch at the anterior extremity; columella tortuous, callous, thickened at the extremity near the spire; epidermis thick, horny, generally black. Subtropical.—Obs.This description includes the two first species of the genus Pirena, Lam. The Melanopsides are known from the Melaniæ by the notch in the aperture. Fig. 315. M. costata.MELAS. Montf.Melania, Auct.MELATOMA. Sw. A sub-genus of Melanopsis. Sw. p. 341.MELEAGRINA. Lam.Margarita.A genus composed of the Pearl Oyster and similar species, separated from Avicula on account of the roundness of their general form, but re-united by Sowerby. For generic characters, see Avicula. Fig. 164. M. margaritifera.MELEAGRIS. Montf.TurboPica, Auct. and similar species, having the aperture oblique, the columella gliding imperceptibly into the outer lip, and having an umbilicus.MELINA. Schum.Perna, Auct.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 fromVolutaprincipally 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.VenusMercenaria, 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.CythereaMeroe, 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 fromHelix, 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 ofMitraFissurella, 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. (FromMollis, 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. (Μονος,monos, single;Κερας,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. (Μονος,monos, single;μυον,myon, muscle.) The second order of Conchifera, consisting of those bivalve shells which have butoneprincipal 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. (Μονος,monos, single;θαλαμος,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. SeePupina.MOURETIA. Gray. "Gadin," Adanson. A genus of patelliform shells, described as differing fromSiphonaria(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.MULINIA. Gray. A genus composed of species ofMactra, Auct. described as having the ligament (properly so called) internal, and lateral teeth simple.Ex.fig. 82. M. bicolor; Mactra, Auct.MULLERIA. Fer.Fam.Ostracea, Lam.—Descr.Irregular, subquadrate, inequivalve, inequilateral, foliaceous, attached, pearly within, green, horny without; hinge irregular, with a partly external ligament, passing to the interior, through a sort of sinus.—Obs.This remarkable shell resembles Etheria in general form and appearance, but is distinguished by having only one muscular impression. It is so rare that, although not very beautiful, a specimen has been known to produce £20. at a sale. Fig. 192.MULTILOCULAR. Many chambered.MULTISPIRAL. (Multus, many,spira, spire.) A term applied to a shell when the spire consists of numerous whorls; or to an operculum of numerous volutions.MULTIVALVE. (Multus, many;valva, valve.) Consisting of numerous valves. There are three kinds of multivalve shells: 1st. Those in which the valves are arranged in pairs, and produce a flattened figure, as Pedunculated Cirripedes, fig. 34 to 43; 2nd. Those in which they are arranged circularly, as Sessile Cirripedes, the valves of which are of two kinds; theopercular, consisting of several valves, which close the aperture, and theparietal, consisting of those which surround the body of the animal in a circular form, fig. 14 to 33. 3rd. Those in which they are arranged in a straight line, as Chiton, fig. 227.MUREX. Auct. (A sharp rock.)Fam.Canalifera, Lam. siphonostoma, Bl.—Descr.Turrited, ventricose, thick, with three or more longitudinal, continuous, branched, spinose or fringed varices; spire prominent, acute; aperture oval, terminating in a posterior, partly closed canal, outer lip varicose, inner lip smooth, laminar; operculum horny, concentric, pointed.—Obs.This genus contains some of the most exquisitely beautiful shells in existence, the richness of their colouring, the ramifications of their varices, would render most species the finest possible subject for the exercise of the painter's art in still life. The most remarkable are the Rosebud Murex, with its pink-tipt fringes, the Venus Comb, with its long rows of parallel spines; the Ducal Murex, the Royal Murex, and many others, which are much sought after by collectors. Murex may be distinguished from Triton by the continuity of the varices, which follow each other in a tortuous direction on the spire. The Ranellæ have only two rows of varices, and have a posterior as well as anterior canal; while Murices have three or more varices, and only one canal. The genus Typhis consists of several small species resembling Murex in every respect, excepting that of having a tubular opening on the upper part of the whorl between each varix. SeeTyphis. The most beautiful Murices are brought from tropical climates. Fig. 395, 396.MURICANTHUS. Sw. A sub-genus of Murex, thus described: "Varices numerous, foliated; spire short; margin of the outer lip with a prominent tooth near the base; Radix.Sw.Zool. Ill. 2nd series. pl. 113, Melanomathus. En. Méth. 418. f. 2." Sw. p. 296. The latter of the two species quoted, however, does not agree with the description, having no prominent tooth on the margin of the outer lip.MURICATED. (Muricatus.) Having sharp points or prickles.MURICIDEA. Sw. A genus of "Muricinæ," Sw. thus described, "Spire more produced, as long or longer than the body whorl; varices numerous; no internal channel at the top of the aperture." Sw. p. 297, and consisting of the following incongruous species, "Lamellosa. Chem. f. 1823, 4. magellanica. En. M. 419. f. 4. peruviana. Ib. f. 5. senticosa, Ib. f. 3. scaber. En. Méth. 419. f. 6. hexagona. Ib. 418. f. 3. erinacea. Mart. f. 1026." Sw. p. 297.MUSCULAR IMPRESSIONS are the marks or areas formed on the interior surface of shells by the muscular fibres which attach the animals to them. Lamarck has divided his Conchifera into two kinds: 1st. Monomyaria, those which have but one adductor muscle, and consequently have but one impression in each valve, as the common Oyster, fig. 180; 2nd. The Dimyaria, those which have two, and consequently have two impressions in each valve. There are other smaller impressions in some shells besides the principal. The palleal impression is a mark or scar passing near the margin of the shell. See Introduction.MYA. Auct.Fam.Myaria, Lam. Pyloridea, Bl.—Descr.Transverse, oval, thick, gaping at both extremities, rounded anteriorly, acuminated posteriorly; hinge with one large, dilate, compressed tooth in one valve, and a suture in the other, containing the cartilage; muscular impressions two, distant, large, irregular; palleal impression with a large sinus.—Obs.Mya may be known by the large, prominent, broad tooth in one valve. In Anatina there is one in each valve, and, in Lyonsia, accessory pieces. Lutraria has cardinal teeth and a ligamentary pit. Few species of Mya are known. They belong to the Northern Hemisphere. M. truncata, fig. 71.MYCETOPODA or MYCETOPUS. D'Orb.Fam.Nayades, Lam.—Descr.Shell elongated, soleniform, inequivalve, inequilateral, gaping anteriorly; muscular impressions very complex.—Obs.These shells are said to terebrate like Pholas. Fig. 151. M. solenoides.MYARIA. Lam. A family belonging to Lamarck's order Conchifera Dimyaria. Containing the following genera:

MELANITHES. Sw. A sub-genus of Melanopsis. Sw. p. 341.

MELANOIDES. Olivier.Melanopsis.Fer.

MELANOPSIS. Fer.Fam.Melaniana, Lam. Entomostomata, Bl.—Descr.Oval or oblong, fusiform; spire acute, sometimes elongated; aperture oblong or oval, pyriform, with a distinct notch at the anterior extremity; columella tortuous, callous, thickened at the extremity near the spire; epidermis thick, horny, generally black. Subtropical.—Obs.This description includes the two first species of the genus Pirena, Lam. The Melanopsides are known from the Melaniæ by the notch in the aperture. Fig. 315. M. costata.

MELAS. Montf.Melania, Auct.

MELATOMA. Sw. A sub-genus of Melanopsis. Sw. p. 341.

MELEAGRINA. Lam.Margarita.A genus composed of the Pearl Oyster and similar species, separated from Avicula on account of the roundness of their general form, but re-united by Sowerby. For generic characters, see Avicula. Fig. 164. M. margaritifera.

MELEAGRIS. Montf.TurboPica, Auct. and similar species, having the aperture oblique, the columella gliding imperceptibly into the outer lip, and having an umbilicus.

MELINA. Schum.Perna, Auct.

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 fromVolutaprincipally 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.VenusMercenaria, 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.CythereaMeroe, 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 fromHelix, 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 ofMitraFissurella, 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. (FromMollis, 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. (Μονος,monos, single;Κερας,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. (Μονος,monos, single;μυον,myon, muscle.) The second order of Conchifera, consisting of those bivalve shells which have butoneprincipal 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. (Μονος,monos, single;θαλαμος,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. SeePupina.

MOURETIA. Gray. "Gadin," Adanson. A genus of patelliform shells, described as differing fromSiphonaria(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.

MULINIA. Gray. A genus composed of species ofMactra, Auct. described as having the ligament (properly so called) internal, and lateral teeth simple.Ex.fig. 82. M. bicolor; Mactra, Auct.

MULLERIA. Fer.Fam.Ostracea, Lam.—Descr.Irregular, subquadrate, inequivalve, inequilateral, foliaceous, attached, pearly within, green, horny without; hinge irregular, with a partly external ligament, passing to the interior, through a sort of sinus.—Obs.This remarkable shell resembles Etheria in general form and appearance, but is distinguished by having only one muscular impression. It is so rare that, although not very beautiful, a specimen has been known to produce £20. at a sale. Fig. 192.

MULTILOCULAR. Many chambered.

MULTISPIRAL. (Multus, many,spira, spire.) A term applied to a shell when the spire consists of numerous whorls; or to an operculum of numerous volutions.

MULTIVALVE. (Multus, many;valva, valve.) Consisting of numerous valves. There are three kinds of multivalve shells: 1st. Those in which the valves are arranged in pairs, and produce a flattened figure, as Pedunculated Cirripedes, fig. 34 to 43; 2nd. Those in which they are arranged circularly, as Sessile Cirripedes, the valves of which are of two kinds; theopercular, consisting of several valves, which close the aperture, and theparietal, consisting of those which surround the body of the animal in a circular form, fig. 14 to 33. 3rd. Those in which they are arranged in a straight line, as Chiton, fig. 227.

MUREX. Auct. (A sharp rock.)Fam.Canalifera, Lam. siphonostoma, Bl.—Descr.Turrited, ventricose, thick, with three or more longitudinal, continuous, branched, spinose or fringed varices; spire prominent, acute; aperture oval, terminating in a posterior, partly closed canal, outer lip varicose, inner lip smooth, laminar; operculum horny, concentric, pointed.—Obs.This genus contains some of the most exquisitely beautiful shells in existence, the richness of their colouring, the ramifications of their varices, would render most species the finest possible subject for the exercise of the painter's art in still life. The most remarkable are the Rosebud Murex, with its pink-tipt fringes, the Venus Comb, with its long rows of parallel spines; the Ducal Murex, the Royal Murex, and many others, which are much sought after by collectors. Murex may be distinguished from Triton by the continuity of the varices, which follow each other in a tortuous direction on the spire. The Ranellæ have only two rows of varices, and have a posterior as well as anterior canal; while Murices have three or more varices, and only one canal. The genus Typhis consists of several small species resembling Murex in every respect, excepting that of having a tubular opening on the upper part of the whorl between each varix. SeeTyphis. The most beautiful Murices are brought from tropical climates. Fig. 395, 396.

MURICANTHUS. Sw. A sub-genus of Murex, thus described: "Varices numerous, foliated; spire short; margin of the outer lip with a prominent tooth near the base; Radix.Sw.Zool. Ill. 2nd series. pl. 113, Melanomathus. En. Méth. 418. f. 2." Sw. p. 296. The latter of the two species quoted, however, does not agree with the description, having no prominent tooth on the margin of the outer lip.

MURICATED. (Muricatus.) Having sharp points or prickles.

MURICIDEA. Sw. A genus of "Muricinæ," Sw. thus described, "Spire more produced, as long or longer than the body whorl; varices numerous; no internal channel at the top of the aperture." Sw. p. 297, and consisting of the following incongruous species, "Lamellosa. Chem. f. 1823, 4. magellanica. En. M. 419. f. 4. peruviana. Ib. f. 5. senticosa, Ib. f. 3. scaber. En. Méth. 419. f. 6. hexagona. Ib. 418. f. 3. erinacea. Mart. f. 1026." Sw. p. 297.

MUSCULAR IMPRESSIONS are the marks or areas formed on the interior surface of shells by the muscular fibres which attach the animals to them. Lamarck has divided his Conchifera into two kinds: 1st. Monomyaria, those which have but one adductor muscle, and consequently have but one impression in each valve, as the common Oyster, fig. 180; 2nd. The Dimyaria, those which have two, and consequently have two impressions in each valve. There are other smaller impressions in some shells besides the principal. The palleal impression is a mark or scar passing near the margin of the shell. See Introduction.

MYA. Auct.Fam.Myaria, Lam. Pyloridea, Bl.—Descr.Transverse, oval, thick, gaping at both extremities, rounded anteriorly, acuminated posteriorly; hinge with one large, dilate, compressed tooth in one valve, and a suture in the other, containing the cartilage; muscular impressions two, distant, large, irregular; palleal impression with a large sinus.—Obs.Mya may be known by the large, prominent, broad tooth in one valve. In Anatina there is one in each valve, and, in Lyonsia, accessory pieces. Lutraria has cardinal teeth and a ligamentary pit. Few species of Mya are known. They belong to the Northern Hemisphere. M. truncata, fig. 71.

MYCETOPODA or MYCETOPUS. D'Orb.Fam.Nayades, Lam.—Descr.Shell elongated, soleniform, inequivalve, inequilateral, gaping anteriorly; muscular impressions very complex.—Obs.These shells are said to terebrate like Pholas. Fig. 151. M. solenoides.

MYARIA. Lam. A family belonging to Lamarck's order Conchifera Dimyaria. Containing the following genera:

1.Anatina.Ligament in a spoon-shaped prominence on the hinge of each valve, shell thin. Fig. 69.2.Mya.Spoon-shaped prominence in one valve; shell thick. Fig. 71.3.Anatinella.A spoon-shaped process in both valves. Fig. 70.4.Lyonsia.An internal bony appendage on the hinge. Fig. 491, 492.5.Myochama.Flat valve attached, a bony appendage on the hinge. Fig. 73.6.Cleidothærus.Deep valve attached, a bony appendage. Fig. 75, 76.7.Cumingia.Ligamentary pit in both valves, spoon-shaped. Fig. 87.

1.Anatina.Ligament in a spoon-shaped prominence on the hinge of each valve, shell thin. Fig. 69.

2.Mya.Spoon-shaped prominence in one valve; shell thick. Fig. 71.

3.Anatinella.A spoon-shaped process in both valves. Fig. 70.

4.Lyonsia.An internal bony appendage on the hinge. Fig. 491, 492.

5.Myochama.Flat valve attached, a bony appendage on the hinge. Fig. 73.

6.Cleidothærus.Deep valve attached, a bony appendage. Fig. 75, 76.

7.Cumingia.Ligamentary pit in both valves, spoon-shaped. Fig. 87.

MYOCHAMA. Stutch. (MyaandChama.)Fam.Myaria, Lam.—Descr.Inequivalve, irregular, attached, subequilateral; attached valve flat, with two marginal, diverging teeth, and one end of a little testaceous appendage fixed between them by a horny cartilage; free valve convex, with umbo incurved and two very minute, diverging teeth, between which the other end of the testaceous appendage is placed; external surface of both valves conforming to the grooves or undulations of the shell to which the specimen is attached; muscular impressions two in each valve; palleal impressions with a short sinus.—Obs.This new genus, of which only one species is known, the M. anomioides from New South Wales, differs from Anomia and Anatina in being attached by the surface of one of the valves, from which circumstance the word Chama is added to its name; the little testaceous appendage bringing it near the Myariæ. Fig. 73, M. anomioides.MYOCONCHA. Sow. (MyaandConcha.)Fam.Cardiacea, Lam.—Descr.Oval, equivalve, oblique; umbones terminal; ventral margin rounded; hinge with an external ligament, and one oblique, elongated tooth in the left valve; impression of the mantle not sinuated.—Obs.The fossil genus has the general form of Mytilus or Modiola, but the hinge of the Conchæ generally.MYOPARA. Lea. (Myoparo, a piratical oar-galley.)Fam.Arcacea, Lam. A genus founded on a minute fossil bivalve shell, somewhat resembling Isocardia in form, but having a series of teeth placed on each side of the umbones. M. costatus, fig. 135.MYRISTICA. Sw. A genus of "Pyrulinæ," Sw. thus described: "Sub-pyriform; spire strong, spiny, or tuberculated, nearly as long as the base; umbilicus either partially or entirely concealed; inner lip vitreous, thin; the outer with an internal and ascending canal; the basal channel wide. Hippocastanea. En. M. 432. f. 4. lineata, Ib. f. 5. melongena. En. Méth. 435. f. 3. nodosa. Chem. 1564. 5." Sw. p. 307.Ex.P. Melongena, Fig.MYRTEA. Turt.Venusspinifera, Auct.Lucinaspinifera, Nonnull. The shells of this genus are described as "Oval, triangular, equivalve, nearly equilateral, closed. Hinge of one valve with a single tooth, and lateral one on each side; of the other valve with two teeth, the lateral ones obscure. Ligament external." British Channel and Mediterranean.MYSCA. Turt. A genus composed of species ofUnio, Auct. which are distinguished by having "strong, transverse, notched, cardinal and long lateral teeth." Unio pictorum.MYSIA. Leach. A genus composed ofTellinarotundata, montagu and other similar species.MYTILACEA. Bl. The fourth family of Lamellibranchiata, Bl. The shells are described as regular, equivalve, frequently with a thick, horny epidermis. A toothless hinge and a linear ligament. This family contains the genera Mytilus and Pinna.MYTILACEA. Lam. A family belonging to the first section of Conchifera Monomyaria, Lam. described as having the ligament partly interior, occupying the greater part of the hinge line, which is straight. The shell is rarely foliaceous. The Mytilaceæ cannot easily be confounded with the Malleaceæ, because the former are generally regular and the latter are irregular, and have a thick internal coating of pearl, beyond which the external coating extends. The genera may be thus distinguished:

MYOCONCHA. Sow. (MyaandConcha.)Fam.Cardiacea, Lam.—Descr.Oval, equivalve, oblique; umbones terminal; ventral margin rounded; hinge with an external ligament, and one oblique, elongated tooth in the left valve; impression of the mantle not sinuated.—Obs.The fossil genus has the general form of Mytilus or Modiola, but the hinge of the Conchæ generally.

MYOPARA. Lea. (Myoparo, a piratical oar-galley.)Fam.Arcacea, Lam. A genus founded on a minute fossil bivalve shell, somewhat resembling Isocardia in form, but having a series of teeth placed on each side of the umbones. M. costatus, fig. 135.

MYRISTICA. Sw. A genus of "Pyrulinæ," Sw. thus described: "Sub-pyriform; spire strong, spiny, or tuberculated, nearly as long as the base; umbilicus either partially or entirely concealed; inner lip vitreous, thin; the outer with an internal and ascending canal; the basal channel wide. Hippocastanea. En. M. 432. f. 4. lineata, Ib. f. 5. melongena. En. Méth. 435. f. 3. nodosa. Chem. 1564. 5." Sw. p. 307.Ex.P. Melongena, Fig.

MYRTEA. Turt.Venusspinifera, Auct.Lucinaspinifera, Nonnull. The shells of this genus are described as "Oval, triangular, equivalve, nearly equilateral, closed. Hinge of one valve with a single tooth, and lateral one on each side; of the other valve with two teeth, the lateral ones obscure. Ligament external." British Channel and Mediterranean.

MYSCA. Turt. A genus composed of species ofUnio, Auct. which are distinguished by having "strong, transverse, notched, cardinal and long lateral teeth." Unio pictorum.

MYSIA. Leach. A genus composed ofTellinarotundata, montagu and other similar species.

MYTILACEA. Bl. The fourth family of Lamellibranchiata, Bl. The shells are described as regular, equivalve, frequently with a thick, horny epidermis. A toothless hinge and a linear ligament. This family contains the genera Mytilus and Pinna.

MYTILACEA. Lam. A family belonging to the first section of Conchifera Monomyaria, Lam. described as having the ligament partly interior, occupying the greater part of the hinge line, which is straight. The shell is rarely foliaceous. The Mytilaceæ cannot easily be confounded with the Malleaceæ, because the former are generally regular and the latter are irregular, and have a thick internal coating of pearl, beyond which the external coating extends. The genera may be thus distinguished:

1.Mytilus.Umbones terminating in a point. Fig. 158.2.Dreissina.The same, with a septiform plate. Fig. 159.3.Modiola.Anterior margin rounded beyond the umbones. Fig. 160.4.Pinna.Open at the posterior extremity. Fig. 162.5.Lithodomus.Cylindrical, living in holes. Fig. 161.

1.Mytilus.Umbones terminating in a point. Fig. 158.

2.Dreissina.The same, with a septiform plate. Fig. 159.

3.Modiola.Anterior margin rounded beyond the umbones. Fig. 160.

4.Pinna.Open at the posterior extremity. Fig. 162.

5.Lithodomus.Cylindrical, living in holes. Fig. 161.

MYTILUS. Auct.Fam.Mytilacea. Lam.—Descr.Equivalve, cuneiform, oblique, smooth, with umbones terminal, pointed, and posterior side broad, rounded; hinge linear, with a long, partly internal ligament; muscular impressions two in each valve, that on the posterior side large, irregular; that on the anterior small; palleal impression irregular.—Obs.The Linnean genus Mytilus included the Modiolæ, which differ from the Mytili in the rounded anterior side; and the Pinnæ, which are large shells, gaping at the posterior extremity. M. achatinus, fig. 158.NÆARA. Gray. A genus composed ofAnatinalongirostrum, Lam. and other similar species.NAIA. Sw. A sub-genus of Castalia, Lam. thus described: "Oval, cardinal teeth beneath the bosses, and deeply sulcated, C. corrugata.Lam.En. Méth. 248. f. 8, picta.Sw.En. Méth. 248. f. 6." Sw. p. 379.NANINIA. Gray. A genus composed of the planorbicular species ofHelix, with large umbilici, and outer lip thin, included in the sub-genus Helicella, Fer.Ex.H. citrina, fig. 280.NASSA. Lam. A genus of small shells united to Buccinum by some authors, but separated by others on account of the little tooth-like projection terminating the columella. N. arcularia, fig. 423.NATICA. Brug.Fam.Neritacea, Lam. Hemicyclostomata, Bl.—Descr.Globose, thick, generally smooth; spire short, pointed, with few volutions; aperture semilunar, entire; outer lip thin; columellar lip oblique, nearly straight, callous; umbilicus with a spiral callosity, terminating behind the columella, and sometimes filling up the cavity; operculum shelly in some species, horny in others; epidermis thin, light, semitransparent.—Obs.The straight, callous, smooth edge of the columella and the callosity serve to distinguish this genus from Nerita, Neritina, Neritopsis and Helix. Fig. 327, 328.NATICARIA. Sw. A sub-genus of Natica, thus described: "Oval; convex above; umbilicus small, open, placed very near the top of the aperture; inner lip reflected; small. N. melanostoma, Mart. 189. f. 1926, 1927. cancellata,Sw.Ib. 189. f. 1939. bifasciata, Griff. Cuv. 1. f. 2." Sw. p. 346.NATICELLA. Guild. A sub-genus of Natica, thus described: "Operculum horny; shell globose, but generally depressed; umbilicus nearly filled up by a vitreous deposition of the inner lip; spire obtuse. N. aurantia. Mart. 189. f. 1934, 1935." Sw. p. 345.NAVICELLA. Lam. (A little ship.)Fam.Neritacea, Lam. Hemicyclostomata, Bl.—Descr.Transversely oval, symmetrical, smooth; aperture entire, oval; dorsal surface convex; outer lip thin; inner lip flat, straight edged; spread over the front surface of the body whorl, and sometimes hiding the apex; apex incurved; operculum testaceous, flat, sub-quadrate, with a lateral articulation.—Obs. This well known genus, of which there are several species, is named Cimber by Montfort. The shells are brought from India, the Isle of France and the Moluccas. Fig. 323, N. elliptica.NAUTELLIPSITES. Parkinson. A generic name proposed to include such species of Nautilus as have been compressed, so as to assume an oval instead of a round form. The genus Ellipsolites of De Montfort consists of species of Ammonites similarly deformed.NAUTILACEA. Bl. The fifth family of Polythalamacea, Bl. the shells of which are described as more or less discoidal, compressed, symmetrically convolute; the last whorl much longer than the others; which are entirely hidden beneath it and advancing beyond the last but one, so as constantly to form a large oval aperture, which is always, however, modified by the last whorl. The septa are united in the greater number of instances and pierced by one or more (?) siphons. This family contains the genera Orbulites, Nautilus, Polystomella and Lenticulina.NAUTILACEA. Lam. The sixth family of Polythalamous Cephalopoda, Lam. containing the genera Discorbites, Siderolites, Polystomella, Vorticialis, Nummulites, Nautilus. To these may be added Simplegas and Endosiphonites. Fig. 472 to 476.NAUTILUS. Auct. (A little boat.)Fam.Nautilacea, Lam. and Bl.—Descr.Convolute, discoid, chambered, symmetrical; spire partly or entirely concealed by the last whorl; aperture modified by the last whorl, wide, sinuated on the dorsal margin; interior surface pearly; septa dividing the chambers simple; siphon discontinuous.—Obs.The shell named Nautilus by Pliny is the Argonauta of modern authors, a thin shell, not chambered. The Nautili are known from the Ammonites by the septa being simple, not sinuated as in the latter genus, and in general the volutions of the spire are not visible. Three or four species are known inhabitants of the Pacific Ocean and Australian Ocean. The fossil species are found in the tertiary, and also in the secondary strata, as low down as the Mountain limestone. N. pompilius, Frontispiece.NAYADES. Lam. A family of the order Conchifera Dimyaria, Lam. described as containing fresh-water bivalve shells, with or without teeth on the hinge. They are all pearly within, and have a thick, rather smooth epidermis without. This family contains a great variety of shells, which have been separated into an immense number of genera, but which G. B. Sowerby, sen. gives very good reasons for uniting under one generic name. The most generally received distinctions are as follows:

NÆARA. Gray. A genus composed ofAnatinalongirostrum, Lam. and other similar species.

NAIA. Sw. A sub-genus of Castalia, Lam. thus described: "Oval, cardinal teeth beneath the bosses, and deeply sulcated, C. corrugata.Lam.En. Méth. 248. f. 8, picta.Sw.En. Méth. 248. f. 6." Sw. p. 379.

NANINIA. Gray. A genus composed of the planorbicular species ofHelix, with large umbilici, and outer lip thin, included in the sub-genus Helicella, Fer.Ex.H. citrina, fig. 280.

NASSA. Lam. A genus of small shells united to Buccinum by some authors, but separated by others on account of the little tooth-like projection terminating the columella. N. arcularia, fig. 423.

NATICA. Brug.Fam.Neritacea, Lam. Hemicyclostomata, Bl.—Descr.Globose, thick, generally smooth; spire short, pointed, with few volutions; aperture semilunar, entire; outer lip thin; columellar lip oblique, nearly straight, callous; umbilicus with a spiral callosity, terminating behind the columella, and sometimes filling up the cavity; operculum shelly in some species, horny in others; epidermis thin, light, semitransparent.—Obs.The straight, callous, smooth edge of the columella and the callosity serve to distinguish this genus from Nerita, Neritina, Neritopsis and Helix. Fig. 327, 328.

NATICARIA. Sw. A sub-genus of Natica, thus described: "Oval; convex above; umbilicus small, open, placed very near the top of the aperture; inner lip reflected; small. N. melanostoma, Mart. 189. f. 1926, 1927. cancellata,Sw.Ib. 189. f. 1939. bifasciata, Griff. Cuv. 1. f. 2." Sw. p. 346.

NATICELLA. Guild. A sub-genus of Natica, thus described: "Operculum horny; shell globose, but generally depressed; umbilicus nearly filled up by a vitreous deposition of the inner lip; spire obtuse. N. aurantia. Mart. 189. f. 1934, 1935." Sw. p. 345.

NAVICELLA. Lam. (A little ship.)Fam.Neritacea, Lam. Hemicyclostomata, Bl.—Descr.Transversely oval, symmetrical, smooth; aperture entire, oval; dorsal surface convex; outer lip thin; inner lip flat, straight edged; spread over the front surface of the body whorl, and sometimes hiding the apex; apex incurved; operculum testaceous, flat, sub-quadrate, with a lateral articulation.—Obs. This well known genus, of which there are several species, is named Cimber by Montfort. The shells are brought from India, the Isle of France and the Moluccas. Fig. 323, N. elliptica.

NAUTELLIPSITES. Parkinson. A generic name proposed to include such species of Nautilus as have been compressed, so as to assume an oval instead of a round form. The genus Ellipsolites of De Montfort consists of species of Ammonites similarly deformed.

NAUTILACEA. Bl. The fifth family of Polythalamacea, Bl. the shells of which are described as more or less discoidal, compressed, symmetrically convolute; the last whorl much longer than the others; which are entirely hidden beneath it and advancing beyond the last but one, so as constantly to form a large oval aperture, which is always, however, modified by the last whorl. The septa are united in the greater number of instances and pierced by one or more (?) siphons. This family contains the genera Orbulites, Nautilus, Polystomella and Lenticulina.

NAUTILACEA. Lam. The sixth family of Polythalamous Cephalopoda, Lam. containing the genera Discorbites, Siderolites, Polystomella, Vorticialis, Nummulites, Nautilus. To these may be added Simplegas and Endosiphonites. Fig. 472 to 476.

NAUTILUS. Auct. (A little boat.)Fam.Nautilacea, Lam. and Bl.—Descr.Convolute, discoid, chambered, symmetrical; spire partly or entirely concealed by the last whorl; aperture modified by the last whorl, wide, sinuated on the dorsal margin; interior surface pearly; septa dividing the chambers simple; siphon discontinuous.—Obs.The shell named Nautilus by Pliny is the Argonauta of modern authors, a thin shell, not chambered. The Nautili are known from the Ammonites by the septa being simple, not sinuated as in the latter genus, and in general the volutions of the spire are not visible. Three or four species are known inhabitants of the Pacific Ocean and Australian Ocean. The fossil species are found in the tertiary, and also in the secondary strata, as low down as the Mountain limestone. N. pompilius, Frontispiece.

NAYADES. Lam. A family of the order Conchifera Dimyaria, Lam. described as containing fresh-water bivalve shells, with or without teeth on the hinge. They are all pearly within, and have a thick, rather smooth epidermis without. This family contains a great variety of shells, which have been separated into an immense number of genera, but which G. B. Sowerby, sen. gives very good reasons for uniting under one generic name. The most generally received distinctions are as follows:

1.Castalia.Two cardinal, one lateral, ribbed teeth. This genus is removed from the family of Trigonacea. Fig. 140.2.Unio.Teeth various. Fig. 142, 145, 149, 148, 147, 151, 141.3.Hyria.Trigonal, alated. Fig. 143, 150.4.Anodon.No teeth. Fig. 152.5.Iridina.Hinge crenated. Fig. 150.

1.Castalia.Two cardinal, one lateral, ribbed teeth. This genus is removed from the family of Trigonacea. Fig. 140.

2.Unio.Teeth various. Fig. 142, 145, 149, 148, 147, 151, 141.

3.Hyria.Trigonal, alated. Fig. 143, 150.

4.Anodon.No teeth. Fig. 152.

5.Iridina.Hinge crenated. Fig. 150.

NECTOPODA. Bl. The first family Nucleobranchiata, Bl. containing the genera Carinaria and Firola; the latter is not a shell.NEMATOPODA. Bl. The first class of the sub-type Malentozoa, Bl. containing all the mollusca with multivalve shells, except Chiton, and divided into the families Lepadicea and Balanidea, corresponding with Lamarck's sessile and pedunculated Cirripedes, and with the Linnæan genus Lepas.NEMATURA. Benson.Fam.Turbinacea, Lam.—Descr.Thin, nearly oval, somewhat compressed from back to front; spire acute, consisting of few rounded whorls; last whorl large, but contracted near the aperture; aperture small, oblique, rounded anteriorly; peritreme continuous, thin; operculum spiral, horny, with few volutions.—Obs.The distinguishing character of this genus is the contraction of the last whorl near the aperture, in which respect it is nearly resembled by the shell called Cyclostoma lucidum. Two recent and one fossil species, all very minute, are described by Sowerby in Loudon's Magazine of Natural History, New Series. Fig. 305.NERINEA. Defr.Fam.Canalifera, Lam.—Descr.Turrited, oblong, sub-canaliculated, consisting of numerous whorls; aperture with a strong fold on the columella, one on the outer lip, and one on the inner lip at the edge of the body whorl.—Obs.This genus is only found in a fossil state usually in the Oolitic beds, it is not resembled by any other; the strong, prominent folds on the three upper angles of the subquadrate aperture present a singular appearance in a section. One species has been named N. Hieroglyphus. We give N. Goodhallii, fig. 374.NERITA. Auct.Fam.Neritacea, Lam. Hemicyclostomata, Bl.—Descr.Smooth or ribbed, semiglobose; spire short, sometimes flat, consisting of few volutions; aperture large, semilunar; outer lip thick, entire; inner lip thickened, dentated at the edge, spread over the body whorl, forming a flattened disc; operculum shelly, spiral, with an appendage by which it is locked under the sharp edge of the columella.—Obs.These marine shells are known from Neritina by the thickness of the shell and the want of the thick, horny, dark coloured epidermis; from Natica by the flat area produced by the spreading of the thickened columellar lip. N. Peloronta, fig. 330. N. polita, fig. 329.NERITACEA. Lam. A family of the first order of Trachelipoda, Lam. containing the following genera:

NECTOPODA. Bl. The first family Nucleobranchiata, Bl. containing the genera Carinaria and Firola; the latter is not a shell.

NEMATOPODA. Bl. The first class of the sub-type Malentozoa, Bl. containing all the mollusca with multivalve shells, except Chiton, and divided into the families Lepadicea and Balanidea, corresponding with Lamarck's sessile and pedunculated Cirripedes, and with the Linnæan genus Lepas.

NEMATURA. Benson.Fam.Turbinacea, Lam.—Descr.Thin, nearly oval, somewhat compressed from back to front; spire acute, consisting of few rounded whorls; last whorl large, but contracted near the aperture; aperture small, oblique, rounded anteriorly; peritreme continuous, thin; operculum spiral, horny, with few volutions.—Obs.The distinguishing character of this genus is the contraction of the last whorl near the aperture, in which respect it is nearly resembled by the shell called Cyclostoma lucidum. Two recent and one fossil species, all very minute, are described by Sowerby in Loudon's Magazine of Natural History, New Series. Fig. 305.

NERINEA. Defr.Fam.Canalifera, Lam.—Descr.Turrited, oblong, sub-canaliculated, consisting of numerous whorls; aperture with a strong fold on the columella, one on the outer lip, and one on the inner lip at the edge of the body whorl.—Obs.This genus is only found in a fossil state usually in the Oolitic beds, it is not resembled by any other; the strong, prominent folds on the three upper angles of the subquadrate aperture present a singular appearance in a section. One species has been named N. Hieroglyphus. We give N. Goodhallii, fig. 374.

NERITA. Auct.Fam.Neritacea, Lam. Hemicyclostomata, Bl.—Descr.Smooth or ribbed, semiglobose; spire short, sometimes flat, consisting of few volutions; aperture large, semilunar; outer lip thick, entire; inner lip thickened, dentated at the edge, spread over the body whorl, forming a flattened disc; operculum shelly, spiral, with an appendage by which it is locked under the sharp edge of the columella.—Obs.These marine shells are known from Neritina by the thickness of the shell and the want of the thick, horny, dark coloured epidermis; from Natica by the flat area produced by the spreading of the thickened columellar lip. N. Peloronta, fig. 330. N. polita, fig. 329.

NERITACEA. Lam. A family of the first order of Trachelipoda, Lam. containing the following genera:

1.Navicella.Apex terminal, not spiral; inner lip septiform. Fig. 323.2.Nerita.Columellar lip septiform, edge with distinct teeth; shell thick. Fig. 330.3.Neritina.Shell thin; columellar lip septiform, edge denticulated; generally a thick, dark coloured epidermis. Fig. 324 to 326.4.Natica.Having an umbilicus behind the columellar lip, with a spiral callosity. Fig. 327, 328.5.Neritopsis.Edge of the columellar lip with a deep notch. Fig. 331.6.Pileolus.Patelliform; apex central; columellar lip septiform, leaving the aperture small. Fig. 332.7.Janthina.Columellar lip linear; aperture angulated. Fig. 333.

1.Navicella.Apex terminal, not spiral; inner lip septiform. Fig. 323.

2.Nerita.Columellar lip septiform, edge with distinct teeth; shell thick. Fig. 330.

3.Neritina.Shell thin; columellar lip septiform, edge denticulated; generally a thick, dark coloured epidermis. Fig. 324 to 326.

4.Natica.Having an umbilicus behind the columellar lip, with a spiral callosity. Fig. 327, 328.

5.Neritopsis.Edge of the columellar lip with a deep notch. Fig. 331.

6.Pileolus.Patelliform; apex central; columellar lip septiform, leaving the aperture small. Fig. 332.

7.Janthina.Columellar lip linear; aperture angulated. Fig. 333.

NERITINA. Lam.Fam.Neritacea, Lam.—Descr.Thin, semiglobose, obliquely oval, smooth, flattish in front; spire short, sometimes depressed, consisting of few rapidly increasing whorls; aperture semicircular; outer lip thin, sharp; columellar lip broad, flat, its inner edge straight, denticulated; operculum testaceous, semicircular, sub-spiral, with an articulating process on the inner edge.—Obs.This genus of fresh-water shells differs from Nerita in the minuteness of the denticulation of the columella, as well as in the characters mentioned in our observations upon the latter genus. N. spinosa, (Clithon, Montf.) fig. 325. N. virginea, fig. 324. N. perversa, Lam. (Velates, Montf.) fig. 326. All the species known up to the present time, with the exception of three, are represented in the author's Conchological Illustrations, parts 86, 87, 90, 91, 94 to 100. The catalogue accompanying these representations enumerates 59 species.NERITOPSIS. Gray.Fam.Neritacea, Lam.—Descr.Sub-globose, thick, cancellated; spire short, composed of few rapidly increasing whorls; aperture transverse, sub-orbicular; outer lip thickened within; columellar lip thick, rather flat, with a large rounded notch in the centre of its inner edge.—Obs.This genus most nearly resembles Nerita, from which it differs in the peculiar notch of the columella. N. granosa, fig. 331.NICANIA. Leach.Astarte, Sowerby. The same asCrassinaof Lamarck.NITIDELLA. Sw. A genus of "Columbellinæ," Sw. thus described: "Bucciniform, small, ovate, smooth, glassy; aperture effuse; outer lip slightly thickened, faintly inflexed, and generally striated internally; inner lip somewhat flattened above; base of the pillar with one or two slight internal folds, or a single angular projection. Columbella nitida,Lam.(fig. 17,c.p. 151.)" Sw. p. 313.NOBIA. Leach.Order, Sessile Cirripedes, Lam. This genus resembles Pyrgoma, Auct. consisting of a conical paries, supported upon a funnel-shaped cavity in the madrepore, but differs in its operculum, which consists of two valves, whereas that of Pyrgoma has four. N. grandis, fig. 29.NODOSARIA. Lam. andOrthocerahave been united by Sowerby under the name of the first.Fam.Orthocerata, Lam. and Bl.—Descr.Straight, chambered, elongated; chambers more or less ventricose; septa perforated by a central siphon.—Obs.This genus consists only of fossils found in sub-appenine tertiary beds. It is placed by De Blainville in one of his divisions of the genus Orthoceras, which is characterized as "species not striated, and with chambers very much inflated." N. æqualis, fig. 465.NODOSE. Having tubercles or knobs.NOGROBS. Montf. A fossil appearing from the figure and description to resemble Belemnites.NONION. Montf. A genus of microscopic Foraminifera.NONIONINA. D'Orb. A genus of microscopic Foraminifera.NOTREMA. Rafinesque. A shell described as composed of three integral valves, concerning which De Blainville puts the query, "ne seroit-ce pas plutôt une Balanide mal observée?"NOVACULINA. Benson. (Novacula, a razor.)Fam.Solenacea, Lam.—Descr.Equivalve, inequilateral, transversely elongated; external ligament communicating with the interior of the shell by an oblique channel; beaks prominent; hinge line nearly straight, with one narrow curved cardinal tooth in one valve, entering between two similar teeth in the other; siphonal scar long; extremities of the shell gaping; epidermis thin, light brown, folding over the edges and connecting the dorsal margins.Hab.Jumna, Gooti, and Ganges. Fig. 63.NUCLEOBRANCHIATA. Bl. The fifth order of the second section of Paracephalophora Monoica, Bl. the shells of which are described as symmetrical, more or less curved, or longitudinally rolled up and very thin. This order contains,Fam.1. Nectopoda, containing Carinaria;Fam.2. Pteropoda, containing Atlanta, Spiratella and Argonauta.NUCLEUS. (A kernel.) Anything forming a centre around which matter is gathered. The nucleus of shells is the first formed part; the first deposit of shelly matter to which the successive layers are added; the apex of the spiral cone, of which most shells are composed. (SeeCone.) The nucleus is formed within the egg in oviparous, and within the old shell in viviparous mollusca. It is frequently more transparent and light than the remainder of the shell, and sometimes falls off; when this occurs the shell is said to be decollated.NUCULA. Lam. (A small nut.)Fam.Arcacea, Bl. and Lam.—Descr.Equivalve, inequilateral, transverse, covered with an epidermis; hinge linear, with a series of sharp, angulated teeth, arranged in a line on each side of the umbones, and a central ligamentary pit; muscular impressions two, simple; palleal impressions not sinuated.—Obs.The row of teeth on each side of the umbones, and the ligamentary pit in the centre of the hinge prevent the pretty little shells of this genus from being confounded with any other. Thirty-four figures are enumerated in the catalogue by Sowerby, sen. which accompanies the Conchological Illustrations of the author. The new species, to the amount of 24, have been figured in parts 14 to 16, of the above mentioned work. Recent Nuculæ are found from the frozen to the torrid zones, and the fossil species occur in nearly all the beds from the Pliocene to the Carboniferous system.NUMMULACEA. Bl. The third family of Cellulacea, Bl. described as containing shells or calcareous bodies, which are characterized as discoidal, lenticular; without the slightest traces of whorls to be seen externally. The whorls are numerous, internal, and divided into a great number of cells, which are separated from each other by imperforate septa. This family contains the genera Nummulites, Siderolites, Vorticialis, Helicites, Orbiculina, Placentula.NUMMULTTES. Lam. (Nummus, money.)Fam.Nautilacea, Lam.—Descr.Orbicular, convolute, shewing no trace of spire externally; interior divided into cells spirally arranged.—Obs.The singular fossils composing this genus receive their name from their external resemblance to a battered coin. Fig. 472. N. lenticulina.NUX. Humph.Cyclas, Lam.NYMPHACEA. Lam. A family belonging to the order Conchifera Dimyaria, Lam. Ligament external, placed on a prominent fulcrum. This family contains the following genera:

NERITOPSIS. Gray.Fam.Neritacea, Lam.—Descr.Sub-globose, thick, cancellated; spire short, composed of few rapidly increasing whorls; aperture transverse, sub-orbicular; outer lip thickened within; columellar lip thick, rather flat, with a large rounded notch in the centre of its inner edge.—Obs.This genus most nearly resembles Nerita, from which it differs in the peculiar notch of the columella. N. granosa, fig. 331.

NICANIA. Leach.Astarte, Sowerby. The same asCrassinaof Lamarck.

NITIDELLA. Sw. A genus of "Columbellinæ," Sw. thus described: "Bucciniform, small, ovate, smooth, glassy; aperture effuse; outer lip slightly thickened, faintly inflexed, and generally striated internally; inner lip somewhat flattened above; base of the pillar with one or two slight internal folds, or a single angular projection. Columbella nitida,Lam.(fig. 17,c.p. 151.)" Sw. p. 313.

NOBIA. Leach.Order, Sessile Cirripedes, Lam. This genus resembles Pyrgoma, Auct. consisting of a conical paries, supported upon a funnel-shaped cavity in the madrepore, but differs in its operculum, which consists of two valves, whereas that of Pyrgoma has four. N. grandis, fig. 29.

NODOSARIA. Lam. andOrthocerahave been united by Sowerby under the name of the first.Fam.Orthocerata, Lam. and Bl.—Descr.Straight, chambered, elongated; chambers more or less ventricose; septa perforated by a central siphon.—Obs.This genus consists only of fossils found in sub-appenine tertiary beds. It is placed by De Blainville in one of his divisions of the genus Orthoceras, which is characterized as "species not striated, and with chambers very much inflated." N. æqualis, fig. 465.

NODOSE. Having tubercles or knobs.

NOGROBS. Montf. A fossil appearing from the figure and description to resemble Belemnites.

NONION. Montf. A genus of microscopic Foraminifera.

NONIONINA. D'Orb. A genus of microscopic Foraminifera.

NOTREMA. Rafinesque. A shell described as composed of three integral valves, concerning which De Blainville puts the query, "ne seroit-ce pas plutôt une Balanide mal observée?"

NOVACULINA. Benson. (Novacula, a razor.)Fam.Solenacea, Lam.—Descr.Equivalve, inequilateral, transversely elongated; external ligament communicating with the interior of the shell by an oblique channel; beaks prominent; hinge line nearly straight, with one narrow curved cardinal tooth in one valve, entering between two similar teeth in the other; siphonal scar long; extremities of the shell gaping; epidermis thin, light brown, folding over the edges and connecting the dorsal margins.Hab.Jumna, Gooti, and Ganges. Fig. 63.

NUCLEOBRANCHIATA. Bl. The fifth order of the second section of Paracephalophora Monoica, Bl. the shells of which are described as symmetrical, more or less curved, or longitudinally rolled up and very thin. This order contains,Fam.1. Nectopoda, containing Carinaria;Fam.2. Pteropoda, containing Atlanta, Spiratella and Argonauta.

NUCLEUS. (A kernel.) Anything forming a centre around which matter is gathered. The nucleus of shells is the first formed part; the first deposit of shelly matter to which the successive layers are added; the apex of the spiral cone, of which most shells are composed. (SeeCone.) The nucleus is formed within the egg in oviparous, and within the old shell in viviparous mollusca. It is frequently more transparent and light than the remainder of the shell, and sometimes falls off; when this occurs the shell is said to be decollated.

NUCULA. Lam. (A small nut.)Fam.Arcacea, Bl. and Lam.—Descr.Equivalve, inequilateral, transverse, covered with an epidermis; hinge linear, with a series of sharp, angulated teeth, arranged in a line on each side of the umbones, and a central ligamentary pit; muscular impressions two, simple; palleal impressions not sinuated.—Obs.The row of teeth on each side of the umbones, and the ligamentary pit in the centre of the hinge prevent the pretty little shells of this genus from being confounded with any other. Thirty-four figures are enumerated in the catalogue by Sowerby, sen. which accompanies the Conchological Illustrations of the author. The new species, to the amount of 24, have been figured in parts 14 to 16, of the above mentioned work. Recent Nuculæ are found from the frozen to the torrid zones, and the fossil species occur in nearly all the beds from the Pliocene to the Carboniferous system.

NUMMULACEA. Bl. The third family of Cellulacea, Bl. described as containing shells or calcareous bodies, which are characterized as discoidal, lenticular; without the slightest traces of whorls to be seen externally. The whorls are numerous, internal, and divided into a great number of cells, which are separated from each other by imperforate septa. This family contains the genera Nummulites, Siderolites, Vorticialis, Helicites, Orbiculina, Placentula.

NUMMULTTES. Lam. (Nummus, money.)Fam.Nautilacea, Lam.—Descr.Orbicular, convolute, shewing no trace of spire externally; interior divided into cells spirally arranged.—Obs.The singular fossils composing this genus receive their name from their external resemblance to a battered coin. Fig. 472. N. lenticulina.

NUX. Humph.Cyclas, Lam.

NYMPHACEA. Lam. A family belonging to the order Conchifera Dimyaria, Lam. Ligament external, placed on a prominent fulcrum. This family contains the following genera:

1.Sanguinolaria.Rostrated, gaping; two cardinal teeth in each valve, includingSoletellinaandLobaria. Fig. 98, 99.2.Psammobia.Quadrate; valves closed, including Psammotæa. Fig. 100.3.Corbis.Thick, fimbriated; a cardinal tooth in the centre of a pit. Fig. 101.4.Grateloupia.A series of small teeth filling a triangular area. Fig. 102.5.Egeria.One single and one double cardinal tooth. Fig. 103.6.Lucina.Rounded; anterior muscular impression tongue-shaped. Fig. 104.7.Tellina.An anterior fold in the ventral margin; lateral teeth. Fig. 105, 106.8.Tellinides.No anterior fold; no lateral teeth. Fig. 107.9.Donax.Margin denticulated; shell wedge-shaped. Fig. 108.10.Capsa.Margin not denticulated, no lateral teeth. Fig. 109.

1.Sanguinolaria.Rostrated, gaping; two cardinal teeth in each valve, includingSoletellinaandLobaria. Fig. 98, 99.

2.Psammobia.Quadrate; valves closed, including Psammotæa. Fig. 100.

3.Corbis.Thick, fimbriated; a cardinal tooth in the centre of a pit. Fig. 101.

4.Grateloupia.A series of small teeth filling a triangular area. Fig. 102.

5.Egeria.One single and one double cardinal tooth. Fig. 103.

6.Lucina.Rounded; anterior muscular impression tongue-shaped. Fig. 104.

7.Tellina.An anterior fold in the ventral margin; lateral teeth. Fig. 105, 106.

8.Tellinides.No anterior fold; no lateral teeth. Fig. 107.

9.Donax.Margin denticulated; shell wedge-shaped. Fig. 108.

10.Capsa.Margin not denticulated, no lateral teeth. Fig. 109.

OBELISCUS. Humph.Trochus, Lam.OBLIQUE. (obliquus.lat.) In a slanting direction. The whorls of spiral univalves generally take an oblique direction in reference to the imaginary axis of the shell. A bivalve is said to be oblique when it slants off from the umbones. An example of this is seen in Avicula, fig. 163.OBSOLETE. (obsoletus, lat.) Worn out, out of use. This term is used to express an indistinctness of character, which sometimes results from the action of sea-water upon unprotected parts of the shell, and sometimes from the deposits of enamel formed in age, and covering the early striæ, ribs, teeth, &c. thereby rendering them less acute.OBTUSE. (obtusus, blunt.) The application of this term is not peculiar to conchology. It is most frequently used to express the character of the spire.Ex. The apex of Megaspira, fig. 294.OCEANUS. Montf. ("Corne d'ammon vivant," Fr.)Nautilusumbilicatus, Auct.OCTHOSIA. Ranz.Clitia, Leach.OCTOCERA. Bl. The first family of the order Cryptodibranchiata, Bl. containing the genus Octopus. A species of which being found in the Argonauta, or Paper Sailor, has given rise to the long continued controversy as to whether it is really the constructor of the shell, or whether it is a mere pirate, and having destroyed the true animal of the Argonaut, has possessed itself of the habitation. This question is now set at rest. SeeArgonauta.OCTOGONAL. (octogonum.) Having eight angles. For an example, see Dentalium, fig. 2.OCTOMERIS. Sow. (οκτω,octo, eight;μερος,meros, part.)Fam.Balanidea, Bl.Order, Sessile Cirripedes, Lam.—Descr.Eight principal valves circularly arranged, forming a compressed cone, attached by a jagged base; aperture enclosed by an operculum, consisting of four valves in pairs.—Obs.The only genus of Sessile Cirripedes agreeing with this in the number of principal valves is Catophragmus, Sow. which is, however, sufficiently distinguished by the several rows of smaller valves by which the principals are surrounded at the base. O. angulosus, fig. 24.ODONTIS. Sow.Monodonta, Lam.ODOSTOMIA. Flem.Descr."Shell conical; aperture ovate; peristome incomplete, retrally, and furnished with a tooth on the pillar." A genus composed of several small species of land shells. Turbo plicatus, Spiralis, Unidentatus, &c. Mont.OLIVA. Auct. (An olive.)Fam.Convoluta, Lam. Angyostomata. Bl.—Descr.Oblong, cylindrical, thick, smooth, shining; spire very short, with sutures distinct, aperture elongated, notched at both extremities; outer lip generally thick; columella thick, obliquely striated, terminated by a tumid, oblique, striated varix; a raised band passing round the lower part of the body whorl.—Obs.The shells composing this well known genus present a great variety of rich markings and brilliant colours. They are marine and tropical. Fossil species are found sparingly in the London Clay and Calcaire-grossièr. The Ancillariæ are distinguished from this genus by the sutures of the whorls being covered by enamel. O. maura, fig. 457.OLIVELLA. Sw. A genus of "Olivinæ," Sw. thus described: "Oliviform; spire (typically) rather produced; the tip acute; inner lip not thickened; outer lip straight; base of the pillar curved inwards, and marked by two strong plaits; upper plaits obsolete or wanting; aperture effused at the base only; biplicata, Tank. Cat. 2332. purpurata. Zool. Ill. ii. 58. f. 1. mutabilis.Say.eburnea. Zool. Ill. ii. 58, f. 2. conoidalis.Lam.No. 57. oryza.Lam.No. 62."OLYGYRA. Say. Mentioned by Ranz as properly belonging to Helicina. H. neritella, Auct.OMALAXIS. Desh. SubsequentlyBifrontia. Desh. Fig. 354.ONISCIA. Sow. (G. B.)Fam.Purpurifera, Lam. Entomostomata, Bl.—Descr.Oblong, sub-ovate, slightly turbinated, cancellated; spire short; aperture elongated; terminating anteriorly in a very short, recurved canal; outer lip thickened, denticulated within; inner lip spread over a portion of the body whorl, granulated.—Obs.The granulated inner lip is the principal character by which this genus is distinguished from Cassidaria. In Oniscia the canal is not so produced. O. oniscus, fig. 409.ONUSTUS. Humph. A genus proposed by Humphrey and adopted by Swainson who describes it thus: "Shell trochiform; the surface irregular, and often covered with extraneous bodies, cemented and incorporated with the calcareous substance of the shell; the under part of the body whorl flattened or concave, umbilicate. O. Solaris. Mart. 173. f. 1700, 1701. Indicus. Ib. 172. f. 1697. 1698." It is probable, from the above description, that Mr. Swainson intended to include Trochus agglutinans of authors. (Genus Phorus, Montf.) Fig. 360.OPERCULAR. Of, or belonging to, the operculum. A term applied to the valves which compose the operculum of multivalve shells, as distinguished from the parietal valves, or those which are arranged circularly and form the body of the shell.OPERCULINA. D'Orb. A genus of microscopic Foraminifera.OPERCULUM. (A cover or lid.) The plate or plates with which many molluscous animals enclose the aperture of their shells, when retired within them. The operculum is sometimes horny, as in Trochus; testaceous or shelly, as in Turbo. It is spiral when from a central or sub-central nucleus, the successive layers take a revolving direction, as in Trochus. It is concentric or annular when the outside edge of each layer entirely surrounds the preceding one. It is unguiculated, when the laminæ are placed side by side, as in Purpura. The opercula of multivalve shells are composed of two or four pieces, which are called the opercular valves. The shelly or membranaceous plate with which some of the animals enclose the aperture of their shells, during the wintry part of the year, for the purpose of protecting them while in a torpid state, and which they get rid of by dissolving the edges, when preparing to emerge from their temporary retirement, must not be considered as the operculum, as it does not belong to or form part of either the animal or its shell, but is produced for the occasion by a secretion of the animal, being deposited in a soft state and subsequently hardening. It is called the epiphragm, and may easily be distinguished from the true operculum by the texture, and by the circumstance of their being soldered to the edge of the aperture. The operculum, on the contrary, is moveable, and is always composed of a series of successive layers, corresponding with the growth of the shell.OPIS. Defr. A genus described by De Blainville as consisting of species of Trigonia which have the umbones sub-spiral, with a large, striated tooth on the hinge. Opis cardissoides, Trigonia, Lam. Opis similis, Sow. Min. Con. pl. 232. f. 2.ORAL. (Os,oris, mouth.) Applied to that part of a shell which corresponds with the mouth of the animal, but very seldom used in this sense.ORBICULA. Lam. (Orbis, an orb.)Fam.Brachiopoda, Lam. Palliobranchiata, Bl.—Descr.Inequivalve, irregular, sub-orbicular, compressed, attached by a fibrous substance passing through a fissure near the centre of the lower valve; upper valve patelliform, with the umbo central; muscular impressions four in each valve, semilunar. South America and West Indies.—Obs.Discina, Lam. is an Orbicula. Crania is known from this genus by having no fissure in the lower valve, but being attached by its substance. Hipponyx has only two muscular impressions in each valve. O. lævis, fig. 201.ORBICULAR. (Orbiculus, a little orb.) Of a round or circular form.ORBICULINA. Lam. A genus of microscopic Foraminifera.ORBIS. Lea. A minute fossil, described as "orbicular, with flat quadrate whorls and aperture square," in other respects resembling Solarium. O. Rotella, fig. 355, 356.ORBITINA. Risso. A genus said to be established upon the nuclei of two land shells.ORBULITES. Lam. A genus separated from Ammonites on account of the last volution covering the spire. This is generally considered as characterizing the Nautili, and distinguishing them from the Ammonites; but there are so many gradations that it seems impossible to maintain the distinction in this respect. Fig. 479, O. crassus, fig. 480, O. discus.OREAS. Montf. Part ofCristellaria, Lam. A genus of microscopic Foraminifera.ORTHIS. Dalman. (ορθος,orthos, straight.)Fam.Brachiopoda, Lam. One of the generic divisions of Brachiopoda by Dalman, thus described: "Hinge rectilinear, with umbones distant; the larger valve with a transverse, basal, smooth area, with a triangular pit." O. basalis, fig. 207.ORTHOCERA. Lam. SeeNodosaria.ORTHOCERATA. Lam. A family of Polythalamous Cephalopoda, Lam. containing the following genera:—

OBELISCUS. Humph.Trochus, Lam.

OBLIQUE. (obliquus.lat.) In a slanting direction. The whorls of spiral univalves generally take an oblique direction in reference to the imaginary axis of the shell. A bivalve is said to be oblique when it slants off from the umbones. An example of this is seen in Avicula, fig. 163.

OBSOLETE. (obsoletus, lat.) Worn out, out of use. This term is used to express an indistinctness of character, which sometimes results from the action of sea-water upon unprotected parts of the shell, and sometimes from the deposits of enamel formed in age, and covering the early striæ, ribs, teeth, &c. thereby rendering them less acute.

OBTUSE. (obtusus, blunt.) The application of this term is not peculiar to conchology. It is most frequently used to express the character of the spire.Ex. The apex of Megaspira, fig. 294.

OCEANUS. Montf. ("Corne d'ammon vivant," Fr.)Nautilusumbilicatus, Auct.

OCTHOSIA. Ranz.Clitia, Leach.

OCTOCERA. Bl. The first family of the order Cryptodibranchiata, Bl. containing the genus Octopus. A species of which being found in the Argonauta, or Paper Sailor, has given rise to the long continued controversy as to whether it is really the constructor of the shell, or whether it is a mere pirate, and having destroyed the true animal of the Argonaut, has possessed itself of the habitation. This question is now set at rest. SeeArgonauta.

OCTOGONAL. (octogonum.) Having eight angles. For an example, see Dentalium, fig. 2.

OCTOMERIS. Sow. (οκτω,octo, eight;μερος,meros, part.)Fam.Balanidea, Bl.Order, Sessile Cirripedes, Lam.—Descr.Eight principal valves circularly arranged, forming a compressed cone, attached by a jagged base; aperture enclosed by an operculum, consisting of four valves in pairs.—Obs.The only genus of Sessile Cirripedes agreeing with this in the number of principal valves is Catophragmus, Sow. which is, however, sufficiently distinguished by the several rows of smaller valves by which the principals are surrounded at the base. O. angulosus, fig. 24.

ODONTIS. Sow.Monodonta, Lam.

ODOSTOMIA. Flem.Descr."Shell conical; aperture ovate; peristome incomplete, retrally, and furnished with a tooth on the pillar." A genus composed of several small species of land shells. Turbo plicatus, Spiralis, Unidentatus, &c. Mont.

OLIVA. Auct. (An olive.)Fam.Convoluta, Lam. Angyostomata. Bl.—Descr.Oblong, cylindrical, thick, smooth, shining; spire very short, with sutures distinct, aperture elongated, notched at both extremities; outer lip generally thick; columella thick, obliquely striated, terminated by a tumid, oblique, striated varix; a raised band passing round the lower part of the body whorl.—Obs.The shells composing this well known genus present a great variety of rich markings and brilliant colours. They are marine and tropical. Fossil species are found sparingly in the London Clay and Calcaire-grossièr. The Ancillariæ are distinguished from this genus by the sutures of the whorls being covered by enamel. O. maura, fig. 457.

OLIVELLA. Sw. A genus of "Olivinæ," Sw. thus described: "Oliviform; spire (typically) rather produced; the tip acute; inner lip not thickened; outer lip straight; base of the pillar curved inwards, and marked by two strong plaits; upper plaits obsolete or wanting; aperture effused at the base only; biplicata, Tank. Cat. 2332. purpurata. Zool. Ill. ii. 58. f. 1. mutabilis.Say.eburnea. Zool. Ill. ii. 58, f. 2. conoidalis.Lam.No. 57. oryza.Lam.No. 62."

OLYGYRA. Say. Mentioned by Ranz as properly belonging to Helicina. H. neritella, Auct.

OMALAXIS. Desh. SubsequentlyBifrontia. Desh. Fig. 354.

ONISCIA. Sow. (G. B.)Fam.Purpurifera, Lam. Entomostomata, Bl.—Descr.Oblong, sub-ovate, slightly turbinated, cancellated; spire short; aperture elongated; terminating anteriorly in a very short, recurved canal; outer lip thickened, denticulated within; inner lip spread over a portion of the body whorl, granulated.—Obs.The granulated inner lip is the principal character by which this genus is distinguished from Cassidaria. In Oniscia the canal is not so produced. O. oniscus, fig. 409.

ONUSTUS. Humph. A genus proposed by Humphrey and adopted by Swainson who describes it thus: "Shell trochiform; the surface irregular, and often covered with extraneous bodies, cemented and incorporated with the calcareous substance of the shell; the under part of the body whorl flattened or concave, umbilicate. O. Solaris. Mart. 173. f. 1700, 1701. Indicus. Ib. 172. f. 1697. 1698." It is probable, from the above description, that Mr. Swainson intended to include Trochus agglutinans of authors. (Genus Phorus, Montf.) Fig. 360.

OPERCULAR. Of, or belonging to, the operculum. A term applied to the valves which compose the operculum of multivalve shells, as distinguished from the parietal valves, or those which are arranged circularly and form the body of the shell.

OPERCULINA. D'Orb. A genus of microscopic Foraminifera.

OPERCULUM. (A cover or lid.) The plate or plates with which many molluscous animals enclose the aperture of their shells, when retired within them. The operculum is sometimes horny, as in Trochus; testaceous or shelly, as in Turbo. It is spiral when from a central or sub-central nucleus, the successive layers take a revolving direction, as in Trochus. It is concentric or annular when the outside edge of each layer entirely surrounds the preceding one. It is unguiculated, when the laminæ are placed side by side, as in Purpura. The opercula of multivalve shells are composed of two or four pieces, which are called the opercular valves. The shelly or membranaceous plate with which some of the animals enclose the aperture of their shells, during the wintry part of the year, for the purpose of protecting them while in a torpid state, and which they get rid of by dissolving the edges, when preparing to emerge from their temporary retirement, must not be considered as the operculum, as it does not belong to or form part of either the animal or its shell, but is produced for the occasion by a secretion of the animal, being deposited in a soft state and subsequently hardening. It is called the epiphragm, and may easily be distinguished from the true operculum by the texture, and by the circumstance of their being soldered to the edge of the aperture. The operculum, on the contrary, is moveable, and is always composed of a series of successive layers, corresponding with the growth of the shell.

OPIS. Defr. A genus described by De Blainville as consisting of species of Trigonia which have the umbones sub-spiral, with a large, striated tooth on the hinge. Opis cardissoides, Trigonia, Lam. Opis similis, Sow. Min. Con. pl. 232. f. 2.

ORAL. (Os,oris, mouth.) Applied to that part of a shell which corresponds with the mouth of the animal, but very seldom used in this sense.

ORBICULA. Lam. (Orbis, an orb.)Fam.Brachiopoda, Lam. Palliobranchiata, Bl.—Descr.Inequivalve, irregular, sub-orbicular, compressed, attached by a fibrous substance passing through a fissure near the centre of the lower valve; upper valve patelliform, with the umbo central; muscular impressions four in each valve, semilunar. South America and West Indies.—Obs.Discina, Lam. is an Orbicula. Crania is known from this genus by having no fissure in the lower valve, but being attached by its substance. Hipponyx has only two muscular impressions in each valve. O. lævis, fig. 201.

ORBICULAR. (Orbiculus, a little orb.) Of a round or circular form.

ORBICULINA. Lam. A genus of microscopic Foraminifera.

ORBIS. Lea. A minute fossil, described as "orbicular, with flat quadrate whorls and aperture square," in other respects resembling Solarium. O. Rotella, fig. 355, 356.

ORBITINA. Risso. A genus said to be established upon the nuclei of two land shells.

ORBULITES. Lam. A genus separated from Ammonites on account of the last volution covering the spire. This is generally considered as characterizing the Nautili, and distinguishing them from the Ammonites; but there are so many gradations that it seems impossible to maintain the distinction in this respect. Fig. 479, O. crassus, fig. 480, O. discus.

OREAS. Montf. Part ofCristellaria, Lam. A genus of microscopic Foraminifera.

ORTHIS. Dalman. (ορθος,orthos, straight.)Fam.Brachiopoda, Lam. One of the generic divisions of Brachiopoda by Dalman, thus described: "Hinge rectilinear, with umbones distant; the larger valve with a transverse, basal, smooth area, with a triangular pit." O. basalis, fig. 207.

ORTHOCERA. Lam. SeeNodosaria.

ORTHOCERATA. Lam. A family of Polythalamous Cephalopoda, Lam. containing the following genera:—

1.Conularia.Conical, externally striated; no siphon. Fig. 469.2.Amplexus.Cylindrical; margins of the septa reflected. Fig. 463.3.Orthoceratites.Straight, gradually conical; septa simple; siphon central. Fig. 464.4.Nodosaria.Divided externally into lobes. Fig. 465.5.Belemnites.Straight, conical; septa simple; siphon lateral; apex solid; internal cast, or nucleus, pyramidal, separable. Fig. 466 to 468.6.Conilites.Like Belemnites, but external shell thin at the apex. Fig. 470.

1.Conularia.Conical, externally striated; no siphon. Fig. 469.

2.Amplexus.Cylindrical; margins of the septa reflected. Fig. 463.

3.Orthoceratites.Straight, gradually conical; septa simple; siphon central. Fig. 464.

4.Nodosaria.Divided externally into lobes. Fig. 465.

5.Belemnites.Straight, conical; septa simple; siphon lateral; apex solid; internal cast, or nucleus, pyramidal, separable. Fig. 466 to 468.

6.Conilites.Like Belemnites, but external shell thin at the apex. Fig. 470.

ORTHOCERATA. Bl. The first family of Polythalamacea, Bl. containing the genera Belemnites, Conularia, Conilites, Orthoceras and Baculites. De Blainville remarks that the genera included in this family are all fossils, and known very imperfectly, in consequence of the greater part of the specimens being only casts.ORTHOCERATITES. Auct.Fam.Orthocerata, Lam. and Bl.—Descr.Straight, conical, divided into numerous chambers by simple septa perforated by a central siphon. O. annulata, fig. 464.OSTEODESMA. Desh.Periploma, Schum.OSTRACEA. (Ostracées, Lam.) A family belonging to the second section of the order Conchifera Monomyaria, the shells of which are described as irregular, foliaceous, sometimes papyraceous, with the ligament wholly or partly interior. The principal difference between the Ostracea and the Pectinides consists in the absence of the auricles and the foliated structure of the shells, for, although the Spondylus has ex-foliations or spines upon the external surface, the shell itself is compact and firm. This family contains the genera Gryphæa, Ostrea, Vulsella, Placuna, Anomia, which may be thus distinguished:—

ORTHOCERATITES. Auct.Fam.Orthocerata, Lam. and Bl.—Descr.Straight, conical, divided into numerous chambers by simple septa perforated by a central siphon. O. annulata, fig. 464.

OSTEODESMA. Desh.Periploma, Schum.

OSTRACEA. (Ostracées, Lam.) A family belonging to the second section of the order Conchifera Monomyaria, the shells of which are described as irregular, foliaceous, sometimes papyraceous, with the ligament wholly or partly interior. The principal difference between the Ostracea and the Pectinides consists in the absence of the auricles and the foliated structure of the shells, for, although the Spondylus has ex-foliations or spines upon the external surface, the shell itself is compact and firm. This family contains the genera Gryphæa, Ostrea, Vulsella, Placuna, Anomia, which may be thus distinguished:—

1.Pedum.Flat, turned up at the sides, an hiatus for the passage of a byssus. A triangular disc on the hinge. Fig. 179.2.Ostrea.Foliaceous, irregular, hinge on a small triangular disc. Including Dendostrea, Ostræa, Exogyra, Gryphæa. Fig. 180 to 183.3.Placuna. Two diverging ribs near the umbones. Fig. 184.4.Placunanomia.The same, but attached by fibres passing through a hole in one valve. Fig. 189 to 191.5.Anomia.No costæ, attached by a bony substance passing through a hole in one valve. Fig. 186 to 188.6.Vulsella.Tongue-shaped, a ligamentary pit on the hinge. Fig. 185.7.Mulleria.Doubtful. Fig. 192.

1.Pedum.Flat, turned up at the sides, an hiatus for the passage of a byssus. A triangular disc on the hinge. Fig. 179.

2.Ostrea.Foliaceous, irregular, hinge on a small triangular disc. Including Dendostrea, Ostræa, Exogyra, Gryphæa. Fig. 180 to 183.

3.Placuna. Two diverging ribs near the umbones. Fig. 184.

4.Placunanomia.The same, but attached by fibres passing through a hole in one valve. Fig. 189 to 191.

5.Anomia.No costæ, attached by a bony substance passing through a hole in one valve. Fig. 186 to 188.

6.Vulsella.Tongue-shaped, a ligamentary pit on the hinge. Fig. 185.

7.Mulleria.Doubtful. Fig. 192.

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