Chapter VII: Part 7

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. ([Greek: Malakos], _malacos_, soft; [Greek: Zôon],
_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 of DOLIUM latilabrum, Kiener, and
other similar species.

MALENTOZOA. Bl. ([Greek: Malakos], _malacos_, soft; [Greek: en], _in_,
[Greek: temnô], _temno_, cut; [Greek: Zôon], _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, including _Meleagrina_. Fig. 163,
164.

2. PERNA. Hinge with linear grooves, including _Pulvinites_. 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 of NATICA, 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. MYA Margaritifera, 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. See CONCHACEA.

MARINE TESTACEA. Those shell-fish which inhabit seas, lakes, &c. of
salt water, in distinction from the _Aquatic_ Testacea, or those which
are found in rivers, ponds or stagnant pools of fresh water: and also
from the _Land_ Testacea, 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 in _Senectus_, 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 of PHOLAS, 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. Of
_symmetrical conical univalves_, length, from front to back; breadth
from side to side; depth from apex to base. Of _spiral univalves_,
length, from apex to anterior of the columella or axis of the shell;
breadth, across from the outer lip to the opposite side. Of
_non-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. ([Greek: Megas], _megas_, great; [Greek: desma],
_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. ([Greek: Megas], _megas_, great; [Greek: odos], _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, resembling _Pupa_, but has a horny operculum; spire not
thickened; teeth or fold on the pillar none, flavula _Sw._ En. Méth.
461. f. 6, brunnea _Guild._ (_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 of
TEREBRATULA, Auct. which are smooth and nearly equivalve. T. lævis, T.
crassa, T. truncula.

MEGASPIRA. Lea. ([Greek: Megas], _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 of
AURICULA, Auct. of a conical form. A. conoidalis, fig. 298.

MELANIA. Auct. ([Greek: Melas], _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;
including _Pirena_. Fig. 315, 316.

2. MELANIA. Aperture not notched; columellar lip not thickened;
including _Auculosa_, _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. TURBO Pica, 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
from _Voluta_ principally on account of the largeness of the aperture,
the lightness of the shell and the thinness of the outer lip. Melo
differs from Cymba in the regularity of the spiral apex, and in the
greater rotundity of the shell. The Melons are beautifully coloured
large shells, found in the seas of the old world. The Melo Indicus has
a certain resemblance to a Melon. Fig. 435. M. Æthiopicus.

MELONIA or MELONITES. A genus of microscopic Foraminifera.

MERCENARIA. Schum. VENUS Mercenaria, Auct. The Money shell which passes
current for cash, under the name "Wampum," among the North American
Indians.

MERETRIX. Lam. Original name for Cytherea, Lam.

MEROE. Schum. CYTHEREA Meroe, sulcata, scripta, hians, Auct. and
similar species. Fig. 117, a.

MESODESMA. Desh. ERYCINA, Lam. according to G. B. Sowerby.

MESOMPHYX. Rafinesque. A genus proposed to be separated from HELIX,
Auct.

MICROTOMA. Sw. A genus of "Purpurinæ," Sw. thus described, "Pillar very
broad and curving inwards; aperture effuse; the notch at the base small
and nearly obsolete; spire very short, patula. Mart. 69. f. 758, 759.
persica. En. Méth. 397. f. 1. unicolor. _Sw._ Chem. f. 1449. Sw. p.
301." Purpura Persica. Fig. 414.

MILIOLA. Lam. A genus of microscopic Foraminifera.

MISILUS. Montf. A genus of microscopic Foraminifera.

MITRA. Lam. (_Mitre._) _Fam._ Columellaria, Lam. Angyostomata;
Bl.--_Descr._ Oblong, thick, covered with a light brown epidermis;
spire long, turrited, acute; aperture emarginated anteriorly; outer lip
thickened; columella with several oblique, thick plaits.--_Obs._ The
pretty small shells composing this genus differ from Marginella, not
only in general form, but in the outer lip not being reflected. Some
species of Voluta, of a more elongated shape than the rest, present a
near approach to the most ventricose of the Mitræ. The apex of Mitra,
however, is always acute, while that of Voluta is generally papillary.
The aperture of the former is narrow and the inner lip thickened, the
contrary being the case with the latter. The shells of this genus are
varied in colouring which is generally rich; and also in form, some
being angulated, some plicated, some coronated and others smooth. The
species are mostly tropical; very few occur so far north as the
Mediterranean. Fossil species are numerous in the Eocene beds. Fig.
431. M. Plicaria. Fig. 432. Conohelix marmorata, Sw.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

MOUTH. The aperture or opening of univalve shells.

MULINIA. Gray. A genus composed of species of MACTRA, 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; the _opercular_, consisting of several valves, which close
the aperture, and the _parietal_, 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. See TYPHIS. 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.

MYOCHAMA. Stutch. (_Mya_ and _Chama_.) _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. (_Mya_ and _Concha_.) _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. VENUS spinifera, Auct. LUCINA spinifera, 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 of UNIO, Auct. which are
distinguished by having "strong, transverse, notched, cardinal and long
lateral teeth." Unio pictorum.

MYSIA. Leach. A genus composed of TELLINA rotundata, 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.

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 of ANATINA longirostrum, 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 of HELIX,
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.

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.

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 as CRASSINA of 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. and ORTHOCERA have 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. (See CONE.)
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, including _Soletellina_ and _Lobaria_. 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.) NAUTILUS umbilicatus,
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. See ARGONAUTA.

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

OCTOMERIS. Sow. ([Greek: oktô], _octo_, eight; [Greek: meros], _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. Subsequently BIFRONTIA. 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 of CRISTELLARIA, Lam. A genus of microscopic
Foraminifera.

ORTHIS. Dalman. ([Greek: orthos], _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. See NODOSARIA.

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.

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:--

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.

OSTRACEA. Bl. The first family of the order Lamellibranchiata, Bl.
containing the genera Anomia, Placuna, Harpax, Ostrea (including
Dendostrea, Sw.) Gryphæa. To these may be added Placunanomia, Brod. and
Mulleria.

OSTREA. Auct. ([Greek: ostreon], _ostreon_, a bone.) _Fam._ Ostracea,
Lam. and Bl.--_Descr._ Irregular, inequivalve, generally inequilateral,
foliaceous, attached by part of the lower valve; hinge sometimes
slightly crenated; destitute of teeth; with the ligament spread upon
the lower part of a central, triangular area, which is divided into
three parts; upper valve much flatter than the lower; muscular
impressions one in each valve, large, sub-central, sub-orbicular, with
one very minute.--_Obs._ The Linnæan Genus Ostrea includes the Pectens
and many other genera so different from each other that, without any
desire to increase the number of genera, it was found necessary by
subsequent authors to separate them. The common Oyster is the type of
this genus as at present constituted, and is well known to be abundant
in various parts of the world. Those which depart furthest from this
type are the Gryphæa, Lam. with a prominent, incurved umbo in the lower
valve. The Dendostrea, Sw. with margins characterized by strongly
angulated folds, throws out arms from the lower valve, by which they
are attached to stems of sea-weed, &c. Fig. 180, O. edulis. Fig. 181,
O. folium. (Dendostrea, Sw.) Fig. 182, Gryphæa incurva. Fig. 183,
Exogyra conica.

OTIDES. Bl. The first order of Scutibranchiata, Bl. containing the
genera Haliotis and Ancylus.