Chapter V: Part 5

CORONULA. (_Corona_, a crown, dim.) _Order_, Sessile Cirripedes, Lam.
_Fam._ Balanidea, Bl.--_Descr._ Six radiated valves, joined side by
side in a circle, forming a depressed cone; internal structure of the
valves, porous or chambered; thickened at the base; operculum
consisting of four valves in pairs; imbedded horizontally in a
cartilaginous substance.--_Obs._ The shells composing this genus are
found partly imbedded in the skin of whales, and the shells of
tortoises, and are therefore destitute of the shelly foundation on
which the Balani and other Coronular Multivalves are supported. C.
Testudinaria, (CHELONOBIA, Leach,) fig. 15. C. Balænarum, (CETOPIRUS,
Ranz.) fig. 16. C. Diadema, (DIADEMA, Ranz.) fig. 17.

CORONULAR MULTIVALVES are those which have their parietal valves joined
together side by side in a circle, surrounding the body of the animal,
so as to form a sort of coronet. This is the characteristic of the
Sessile Cirripedes of Lamarck's system, the Balanidea of De Blainville.

CORRODED. (_Corrodo_, eat away, consume.) The umbones, apices, and
other thick parts of shells, are frequently worn away or consumed by
the action of the element in which they exist. As the thickest parts of
some shells are the most subject to this operation, it appears to the
author to arise from the outer surface of the shell, being less under
the influence of the animal juices than the other parts; and therefore,
more exposed to the influence of the surrounding element. This,
however, is not the case with respect to the Nayades and other
fresh-water shells; with these, corrosion does not take place until
after the thick epidermis which covers them, becomes wounded by some
means or other, and then the animal thickens its shell within as fast
as it is corroded without.

CORTALUS. Montf. (Conch. Syst. 1. 115.) A genus of microscopic
Foraminifera, placed by De Blainville in a division of the genus
Rotalites.

COSTATED. Ribbed, as Cardium Angulatum, fig. 123.

COSTELLARIA. A sub-genus of the genus Tiara, Sw. (Mitra.) C. rigida.
Swainson, Zool. Ill. 1st series, pl. 29.

COWRY. A common name for shells of the genus Cypræa.

CRANIA. (_Cranium_, a skull.) _Fam._ Rudistes, Lam. _Order_,
Pallio-branchiata, Bl.--_Descr._ Inequivalve, equilateral, irregular,
sub-quadrate; upper valve patelliform, conical, with the umbo near the
centre; lower valve attached by its outer surface; muscular
impressions, 4 in each valve; two large, posterior, distant; two small,
near to each other, central. No hinge teeth; no ligament.--_Obs._ This
genus properly belongs to the Brachiopoda, Lam. It differs from
Orbicula in the mode of attachment, which in the latter, is by a byssus
passing through the lower valve, and not by the valve itself. Hipponyx
has only two muscular impressions in each valve. The name of this genus
is derived from the inner surface of the attached valve, which presents
a remarkable resemblance to the facial portion of a human skull. This
appearance is caused by the situation and elevated edges of the
muscular impressions. Fig. 197. Coasts of Britain and Mediterranean.

CRASSATED. (_Crassus_, thick.) Used to express a thickness in the
substance of a shell. _Ex._ Glycimeris, fig. 67.

CRASSATELLA. Lam. (_Crassus_, thick.) _Fam._ Mactracea, Lam. Conchacea,
Bl.--_Descr._ Equivalve, inequilateral, close, thick, rounded
anteriorly, rostrated posteriorly, with denticulated margins, smooth,
or ribbed transversely; hinge with a triangular pit containing the
cartilage, two anterior cardinal teeth, and a posterior depression in
one valve; one anterior tooth and a slight anterior marginal elevation,
and a posterior elevation in the other valve. Muscular impressions
distant, strongly marked. Palleal impression not sinuated.--_Obs._ The
few recent species known are marine, several being brought from the
coasts of New Holland. Fossil species are found in Calcaire-grossier
and London clay. The Crassatella are known from the Veneres, &c., by
the ligamentary pit in the hinge, and from Lutraria and Mactra by the
thickness and closeness of the shell. Fig. 84, C. rostrata.

CRASSINA. Lam. ASTARTE, Sow.

CRASSIPEDES. Lam. (_Crassus_, thick; _pes_, foot.) The first section of
the order Conchifera Dimyaria, Lam. In this section the foot of the
animal is thick, and the shell gapes considerably. It is divided into
the families Tubicolæ, Pholadidæ, Solenidæ, and Myaria. Fig. 44 to 76.

CRASSISPIRA. Sw. A genus separated from COLUMBELLA, Auct. for which Mr.
Swainson quotes "Pleurotoma Bottæ, Auct." Crassispira fasciata, Sw.
Lardn. Cyclop. Malac. p. 313.

CRENATED. (_Crena_, a notch.) Applied to small notches, not
sufficiently raised or defined, to be compared to teeth. _Ex._ The
hinge of Iridina, fig. 150.

CRENATULA. Lam. _Fam._ Malleacea, Lam. Margaritacea, Bl.--_Descr._
Compressed, foliated, irregular, sub-equivalve, inequilateral, oblique;
umbones terminal; hinge linear, nearly straight, with a series of
excavations, containing the cartilage, while the intervening ridges are
covered with the ligament, properly so called. Muscular impression
oblong, indistinct.--_Obs._ This genus is known from Perna by the
hinge, which in the latter is composed of a series of regular,
straight, ligamentary grooves placed across it. In Crenatula also there
is no passage for the byssus, as in Perna. C. Mytiloides, fig. 168.
Coasts of the Red Sea.

CRENULATED. Finely crenated or notched.

CREPIDULA. Lam. (_Crepidula_, a little slipper.) _Fam._ Calyptracea,
Lam. and Bl.--_Descr._ Oval, irregular, patelliform; apex lateral,
incurved, or sub-spiral; external surface convex, smooth, ribbed,
waved, or covered with spines; interior concave, smooth, with a
flattish septum reaching nearly half across the cavity; epidermis light
brown.--_Obs._ The difference between this genus and Calyptræa is that
in the latter, the septum is more free from the sides of the shell, so
that, instead of forming a regular plate, covering half the aperture,
it assumes a variety of shapes, and in some is cup-shaped, in others
forked, and in some forms a little angular shelf. Indeed, the
variations are so numerous that I think it would be better to throw the
two genera into one, and then divide them into smaller groups. Some
species of Calyptræa are farther removed from each other with respect
to the characters of the septum and general form of the shell, than
they are from the Crepidulæ. Fig. 239. Mediterranean, North and South
America, East and West Indies, New South Wales, &c.

CREPIDULINA. Bl. CRISTELLARIA, Lam. Microscopic.

CRESEIS. Ranz. _Order_, Pteropoda, Lam.--_Descr._ Thin, fragile,
transparent, pyramidal, pointed; with a dorsal ridge produced into a
point at the edge of the aperture.--_Obs._ The species found in the
Mediterranean is named C. Spinifera (fig. 222), from its resemblance to
a thorn.

CREUSIA. Leach. (_Creux_, se. Fr. a cavity.) _Fam._ Balanidea, Bl.
_Order_, Sessile Cirripedes, Lam.--_Descr._ A depressed cone,
consisting of four valves, supported upon, and jointed to, a cup-shaped
cavity formed in the Madrepores, in which it resides. Aperture
quadrilateral, closed by an operculum of four valves.--_Obs._ This
genus is distinguished from Pyrgoma, which is supported on the edge of
a similar cup-shaped cavity, by the paries being composed of four
valves, whereas in Pyrgoma, it consists of a single piece. Fig. 28, C.
Gregaria. East Indies.

CRICOSTOMATA. Bl. The second family of Asiphonibranchiata, Bl. It is
thus described: "shell equally (with the animal) variable in general
form, but of which the aperture, always nearly round, is completely
closed by the shelly or horny operculum; whorls few, and apex
sublateral." This family agrees in some measure with the family
Turbinacea of Lamarck, and with the genus Turbo in the system of
Linnæus. It contains the genera Pleurotomaria, Delphinula, Turritella,
Proto, Scalaria, Vermetus, Siliquaria, Magilus, Valvata, Cyclostoma,
and Paludina.

CRIOCERATITES. A genus composed of species of Ammonites, with
disconnected whorls. C. Duvallii, fig. 482.

CRIOPUS. Poli. CRANIA, Auct.

CRISTACEA. Lam. The third family of Polythalamous Cephalopoda, Lam.
This family is described as including shells of the following
characters:--"Multilocular, flattened, nearly reniform; the chambers
gradually increasing in length, as they approach the outer arched
margin, and appearing to revolve round an eccentric, more or less
marginal axis. The Cristacea contain the genera Renulina, Cristellaria,
and Orbiculina."

CRISTACEA. Bl. The third family of Polythalamia, Bl. containing the
genera Crepidulina, (Cristellaria, Lam.) Oreas and Linthuris.

CRISTARIA. Schum. DIPSAS Plicatus, Leach. ANODON tuberculatus, Fer.

CRISTELLARIA. Lam. CREPIDULINA, Bl. _Fam._ Cristacea, Lam. and
Bl.--_Descr._ Semidiscoidal, chambered; whorls contiguous, enlarging
progressively; spire eccentric, sublateral; septa imperforate.
Microscopic.

CRYPTA. Humph. CREPIDULA, Lam.

CRYPTELLA. Webb. ([Greek: Kruptô], to conceal.) TESTACELLUS Ambiguus of
Ferrusac. Published in Sowerby's Genera of Shells as PARMACELLA
calyculata.--_Descr._ A small patelliform shell, with a very short
papillary spire; and the aperture irregularly expanded. Fig. 256.
Canary Islands.

CRYPTOCONCHUS. Bl. A genus composed of species of Chiton, the valves of
which are covered by the integument, as Chiton porosus of Burrows. Ch.
amiculatus of Pallas.

CRYPTODIBRANCHIATA. Bl. The first order of the class Cephalophora, Bl.
containing families of molluscous animals destitute of shells.

CRYPTOSTOMA. Bl. Differs from SIGARETUS, Lam. principally in the soft
parts of the animal. De Blainville remarks that he is acquainted with
only two species (from the Indies), which he can with decision refer to
the genus, but he thinks that many of the Lamarckian Sigareti may very
probably be found to belong to it, as soon as the soft parts shall be
known. The species which he figures is Cryptostoma Leachii. (Manuel de
Malacologie, pl. 42. fig. 3.)

CTENOCONCHA. Gray. Described as having many characters in common with
the Solens, the teeth like Nucula, but the cartilage entirely external.
SOLENELLA, Sow.?

CUCULLÆA. Lam. (_Cucullus_, a hood.) _Fam._ Arcacea, Lam.--_Descr._
Sub-quadrate, nearly equivalve, sub-equilateral, deep; hinge
rectilinear, with a series of angular teeth, small near the umbones,
larger and more oblique towards the extremities; umbones separated by a
flat external area, on which the ligament is spread. Anterior muscular
impression produced into a sharp-edged plate or ledge, projecting from
the side of the shell. Posterior muscular impression flat and
indistinct.--_Obs._ This genus very much resembles Arca in general
form, but differs in the oblique, lengthened character of the remote
teeth, and in the singularly prominent edge of the muscular impression.
China. Fig. 133, C. Auriculifera.

CUCUMIS. Klein. MARGINELLA, Auct.

CULTELLUS. Species of LUTRARIA, Lam. which have the umbones placed near
the extremity of the shell. _Ex._ L. Solenoides, fig. 78.

CUMA. Humph. FUSUS and FASCIOLARIA, Lam.

CUMINGIA. Sow. _Fam._ Mactracea, Lam.--_Descr._ Equivalve,
inequilateral, transverse, rounded anteriorly, subrostrated
posteriorly. Hinge with a central spoon-shaped cavity in each valve,
containing the cartilage; a very small anterior cardinal tooth in each
valve; two lateral teeth in one valve, none in the other: muscular
impressions two in each valve, distant; palleal impression with a very
large posterior sinus.--_Obs._ The species known at present are found
in sand, in the fissures of rocks in Tropical climates. They resemble
Erycina in general form and character, but differ in having the
internal cartilage placed in a prominent spoon-shaped process, while
that of Erycina is contained in a hollow which sinks under the umbones.
This genus should be placed near Amphidesma. Cumingia mutica, fig. 87.

CUNEIFORM. (_Cuneus_, a wedge.) Wedge-shaped, as Donax, fig. 108.

CUNEUS. Megerle. VENUS Meroe, Linn. and similar species.

CUNICULA. Sw. A sub-genus of Uniones, thus described:--"Ovate, oblong;
bosses thick, but depressed; cardinal teeth moderate. C. planulata,
patula, rubiginosa, secura, purpurascens."

CURVED. Arched or bent. _Ex._ Dentalium, fig. 2.

CURVULA. Rafinesque. A fossil imperfectly described as differing from
Pinna, in being inequivalve.

CUVIERIA. Ranz. (Baron Cuvier.) _Class_, Pteropoda, Lam.--_Descr._
Thin, transparent, glassy, cylindrical, rounded and inflated at the
closed extremity, compressed towards the opening, so as to render it
oval. This genus differs from Vaginula in being rounded, instead of
pointed, at the lower extremity. Mediterranean. Fig. 223, C. Columella.

CYCLAS. Brug. _Fam._ Conques Fluviatiles, Lam. Conchacea, Bl.--_Descr._
Orbicular, thin, subovate, ventricose, sub-equilateral, equivalve;
cardinal teeth minute, one more or less complicated in the left valve,
two diverging in the right; lateral teeth elongated, compressed,
laminar, acute, doubled in the left valve; ligament external; epidermis
thin, horny.--_Obs._ The Cyclades are viviparous, and abound in
ditches, ponds, slow streams, &c. in Europe and North America. The
genus Pisidium has been separated on account of a difference in the
animal, and may be known from Cyclas by being less equilateral, and the
anterior side being the longest. Fig. 111, C. Rivicola.

CYCLOBRANCHIATA. Bl. The third order of the second section of
Paracephalophora Monoica, Bl. containing no genera of Testaceous
Mollusca.

CYCLOCANTHA. Sw. A genus of "Trochidæ," consisting of Turbo stellaris
and T. Calcar, and corresponding with the genus Calcar, Montf.

CYCLONASSA. Sw. A genus of "Nassinæ," Sw. consisting of Nassa
Neritoidea, and corresponding with the genus Cyclops, Montf.

CYCLOPHORUS. Montf. A generic name proposed for those species of
Cyclostoma, Auct. which have an umbilicus. C. Involvulus, fig. 304,
would be the type of this genus.

CYCLOPS. Montf. NASSA Neritoidea, Auct. fig. 424.

CYCLOSTOMA. Auct. ([Greek: kuklos], _cyclos_, round; [Greek: stoma],
_stoma_, mouth.) _Fam._ Colimacea, Lam. Cricostomata, Bl. A genus of
land shells varying in shape from that of Pupa to that of a flat orb;
the aperture is generally circular and the peritreme uninterrupted,
thickened and sometimes reflected, the operculum is shelly and spiral.
Two other genera of land shells are provided with opercula, and
consequently might be confounded with this genus. In Helicina, the
operculum is concentric and the peritreme is not continuous; while in
the small genus hitherto almost unknown of Pupina, the peritreme is not
continuous and there is a glassy enamel over the whole of the external
surface. In the plates we have represented, C. ferrugineum, fig. 303;
C. involvulus, fig. 304.

CYCLOTUS. Guild. A sub-genus of Cyclostoma, consisting of those species
which are discoidal, as C. Planorbulum. Fig. 530.

CYLINDER. Montf. CONUS textile, Auct. (fig. 461) and other species
having a cylindrical form.

CYLINDRELLA. Sw. A genus of the family "Ovulinæ," Sw. composed of
cylindrical species of Ovulum? The wood-cut illustrating this genus has
the appearance of a Bulla.

CYLINDRICAL. ([Greek: kulindros], a cylinder.) This like other
mathematical terms is used with great latitude by Conchologists, and
applied to any shell the sides of which are nearly parallel, with the
extremities either rounded, flat, or conical. _Ex._ Oliva, fig. 457.

CYLLENE. Gray. _Fam._ Purpurifera, Lam.--_Descr._ Oval, thick, with a
short acute spire; an oval aperture terminating anteriorly in a slight
emargination, posteriorly in a short canal; a fold at the lower end of
the body whorl; outer lip thick, striated within; angle of the whorls
tuberculated.--_Obs._ This genus of small marine shells resembles
Voluta in general character, but differs in having a smooth columella
without folds. Recent, Pacific Ocean; Fosil, London clay. Fig. 425.

CYMBA. Brod. (_Cymba_, a boat or skiff.) _Fam._ Columellaria,
Lam.--_Descr._ Smooth, ventricose, with a very short, mammillated, rude
spire; and a very large, wide aperture, terminated anteriorly in a deep
emargination; posteriorly in a flat ledge, which separates the outer
lip from the body whorl; columella with three or four oblique, laminar,
projecting folds, terminating in a point; outer lip thin, with its edge
sharp; epidermis smooth, brown, covered partly or entirely by the
glassy enamel, which, commencing with the outer lip, spreads over the
body of the shell.--_Obs._ These very elegant shells, found in Africa,
are distinguished from the true Volutes by the shapeless, mammillated
apex of the short spire, by the large size of the aperture, and by the
horizontal ledge which separates the outer lip from the body whorl. The
genus Melo, also separated by Mr. Broderip from the Volutes, agrees
with Cymba in some respects, but differs in the regularity of the
spire. Fig. 434, C. Porcina.

CYMBIOLA. Sw. The generic name for a group of Volutes, described as
"armed with spinous tubercules, sometimes smooth, but never ribbed;
spiral whorls gradually diminishing in size, but not distorted; apex
thick and obtuse; pillar with four plaits." Mr. Swainson remarks that
this genus is chiefly distinguished by the obtuse, but not irregular
spire. The typical species are stated to be V. Rutila and V.
Vespertilio, fig. 433. Tropical.

CYMBULIA. (Dim. from _Cymba_.) _Fam._ Pteropoda, Lam. An extremely
light, cartilaginous covering of a molluscous animal, so named from its
similarity in shape to a boat. We mention it here on account of its
similarity to the shelly or glassy covering of other Pteropods, to
which, although membranaceous, it is evidently analogous. The Cymbuliæ
are found in the Mediterranean.

CYPRÆA. Auct. _Fam._ Enroulées, Lam. Angyostomata, Bl.--_Descr._ Oval
or oblong, ventricose, convolute, covered by an enamel, generally
smooth and shining. Spire short, nearly hid. Aperture long, narrow,
terminating in a short canal at both extremities. Outer lip dentated,
thickened, inflected. Inner lip dentated, thickened, reflected over
part of the body whorl.--_Obs._ These shells are so distinguished by
the two rows of teeth arranged on each side of the aperture; the
thickened front formed by the inner and outer lips; and the enamel
deposited over the back of the shell from the mantle of the animal
which envelopes it, that there is no danger of confounding them with
any other genus, except in a young state. Before they have arrived at
the full growth, the front is not thickened, and the outer lip is thin,
not inflected, nor are the teeth formed. In this state the shell
resembles, in some degree, an Oliva. Some species are striated, ribbed,
or tuberculated, but the generality are smooth. Most species belong to
tropical climates, only one to Great Britain. The C. Moneta is current
as money in some parts of Africa, and many species are worn as
ornaments by the South Sea Islanders. The colouring in most species is
exceedingly rich, and arranged in every variety of spots, patches,
rings, lines, bands and clouds. The species most esteemed by collectors
are C. Mappa, C. Testudinaria, C. Pustulata, C. Aurora, C. Princeps, of
which only two specimens are known, C. Leucodon, &c. See also
Cypræovulum, Trivea and Luponia. The fossil species are principally
from the Calc-grossier, the London Clay, Crag, &c. Fig. 445 to 450. The
latest revision of this genus has been effected by Mr. G. B. Sowerby,
sen., who has published a complete catalogue in his son's Conchological
Illustrations. This catalogue enumerates 130 species, the whole of
which are figured in parts 1 to 8, 101 to 131 of the above mentioned
work.

CYPRÆCASSIS. Stutch. (Cypræa and Cassis.)--_Descr._ Shell, when young,
striated, reticulated, or tuberculated; outer lip simple: when mature,
outer lip involute and toothed; columellar lip also toothed; aperture
straight, anteriorly terminated by a recurved canal, posteriorly by a
shallow channel. Animal with the mantle bilobed; operculum
none.--_Obs._ The reasons given for separating this genus from Cassis,
are, 1st, That the shells of the latter have an operculum, while those
of the proposed genus have none. 2nd, That the Cypræcassides do not
form a complete, thickened lip, before the full period of their growth,
like the Cassides. 3rd, That the Cypræcassides have no epidermis. The
species mentioned as probably belonging to Cypræcassis are C. rufa, the
type; C. coarctata, and C. Testiculus, Auct. The establishment of this
genus has been opposed on the ground that indications of epidermis are
discoverable in some specimens of C. rufa; that some specimens of the
same species and Testiculus have been examined, and found to have
formed slightly thickened and dentulated outer lips at very early
periods of growth, while many of the other Cassides are destitute of
varices, and that an operculum of C. coarctata was brought to this
country by Mr. Cuming. It is probable, however, that an increased
knowledge of facts might go far to establish the separation. C.
Testiculus, fig. 412.

CYPRÆADIA. Sw. A genus of the family "Cypræidæ," Sw. thus
described:--"Cypræform; the base contracted; the body whorl not
flattened beneath; shell cancellated; aperture of equal breadth
throughout; a few thickened, short teeth on the pillar; lip at the
base, which is not internally concave. C. cancellata, Sw. Fossil only,
differing from Trivea in its contracted base, in the inequality of its
aperture, and the equal convexity of the inner lip within." (Sw. Lardn.
Cyclop. Malac. p. 325.) Cyprædia, fig. 564.

CYPRÆLA. Sw. A genus formed for the reception of Ovulum verrucosum,
Auct. which has a circular depression at each extremity. It is the same
as the genus Calpurnus of De Montfort. Ovulum verrucosum, fig. 441.

CYPRÆOVULUM. Gray. A genus of Cypræidæ thus described, "shell like a
cowry, but front end of columella covered with regular cross-ribs, like
the rest of the base, internally produced into an acute toothed ridge.
Shell pear-shaped, cross-ridged." C. capense, fig. 444. South Africa.

CYPRICARDIA. Lam. _Fam._ Cardiacea, Lam.--_Descr._ Equivalve,
inequilateral, subquadrate, transversely elongated, with the anterior
side very short; hinge with three cardinal teeth and one remote lateral
tooth in each valve; muscular impressions two in each valve; ligament
external.--_Obs._ This genus is distinguished from Cardita by the three
cardinal teeth. The mollusca of this genus are marine. C. angulata,
fig. 125. Pacific Ocean.

CYPRINA. Lam. _Fam._ "Conques Marines," or Marine Conchacea.--_Descr._
Equivalve, inequilateral, sub-orbicular; umbones curved obliquely;
hinge with three diverging cardinal and one remote lateral teeth in
each valve; ligament external; muscular impressions two in each valve;
palleal impression having a slight posterior sinus; epidermis thick,
rough brown.--_Obs._ The Cyprinæ belong to the Northern hemisphere. The
recent species are not numerous. Fossil species are found in the
tertiary deposits. Cyprina may be known from Venus by the remote
lateral tooth and the thick epidermis. C. vulgaris, fig. 116.

CYRENA. Auct. _Fam._ Fluviatile Conchaceæ, Lam. Conchacea, Bl--_Descr._
Suborbicular, equivalve, inequilateral, ventricose, corroded at the
umbones, thick, covered with a thick epidermis; hinge with three
cardinal and two remote lateral teeth in each valve. Muscular
impressions two in each valve; palleal impression not sinuated.--_Obs._
This genus is distinguished from Venus, Cytherea and Cyprina, by having
two remote lateral teeth; and from Cyclas by the thickness of the
shell. This genus is mostly fluviatile; the recent species are
tropical, and the fossil are found in the newest formations. Fig. 113,
C. fuscata.

CYRENELLA. Desh. See CYRENOIDES.

CYRENOIDES. Joannis. CYRENELLA, Desh. _Fam._ Conques Fluviatiles,
Lam.--_Descr._ Equivalve, subequilateral, ventricose, thin, covered
with a reddish brown epidermis, corroded at the umbones, with a slight
posterior fold. Hinge thin, with three diverging cardinal teeth in each
valve, and a very slight posterior fold in the right valve. Ligament
not very tumid.--_Obs._ This fresh-water shell differs from Cyclas and
Cyrena in the want of lateral teeth, and from the latter in the
thinness of the shell. Fig. 114.

CYRTIA. Dalman. ([Greek: Kurtos], curtos, gibbose.) _Fam._ Brachiopoda,
Lam.--_Descr._ "Hinge rectilinear; with the back elevated into a
semicone or half-pyramid, the cardinal side perpendicularly
_plane_."--_Obs._ This genus of fossil Brachiopoda forms part of the
genus Spirifer, Sow. C. exporrecta, (Anomites exporrecta, Nonnull.)
fig. 204.

CYTHEREA. Lam. _Fam._ "Conques Marines," Lam.--_Descr._ Equivalve,
inæquilateral, oval, lenticular, or sub-trigonal; hinge with two or
more short, diverging cardinal teeth, and one anterior approximate
lateral tooth in each valve.--_Obs._ The Cythereæ are distinguished
from the Veneres by the lateral tooth. C. Meretrix, fig. 117, and 117,
_a. b. c. d._

DACTYLUS. Humph. MARGINELLA, Auct.

DARACIA. Gray. A subgenus of Pyrgoma, including a species which is
remarkable for the irregularity of its form. It grows upon a species of
Monticularia, and the margin takes the shape of the lobes by which it
is surrounded. The aperture is large, and completely closed by the
operculum. Daracia (Pyrgoma) Monticulariæ, fig. 489, 490.

DATE. A common name given to shells of the genus Pholas, on account of
their cylindrical form and consequent resemblance to the fruit. For the
same reason the name Pholas Dactylus has been given by Naturalists to
the species which we represent, fig. 66.

DEAD SHELL. A term used among collectors to signify that the shell has
been exposed on the sea-shore after the animal has ceased to live. A
shell in this condition is worn down by attrition, and loses its beauty
and brilliancy of colouring by being subject to the action of salt
water. A dead shell may be known by a certain hoary whiteness spread
over its surface.

DECACERA. Bl. The second family of the order Cryptodibranchiata, Bl.
containing the genera Calmar and Sepia, which have no shells.

DECADOPECTEN. Rüppell. PECTEN _Plica_, Linn. Fig. 172, having a
plicated hinge.

DECOLLATED. (_Decollari_, to be beheaded.) The apex or nucleus of some
shells being composed of a more fragile substance than the rest, has a
tendency to fall off. The reason of this probably is that the animal
withdrawing from that part, leaves it unprotected. When it falls off,
the hole is stopped up by a septum filling the cavity of the volution,
so as to exclude the air: the shell is then said to be decollated.
_Ex._ Bulinus decollatus, fig. 289.

DECUSSATED. Intersected by striæ crossing each other. _Ex._ Rissoa,
fig. 346.

DELPHINULA. Montf. (_Delphinus_, a dolphin.) _Fam._ Scalariens, Lam.
Cricostomata, Bl.--_Descr._ Orbicular, depressed, thick, rugose; whorls
few, angulated, branched at the angles; aperture pearly, rounded or
sub-quadrate; peritreme continuous, thickened; operculum horny,
composed of numerous whorls.--_Obs._ Several fossil species are found
in the tertiary deposits. D. laciniata, fig. 352. Recent species belong
to tropical climates.

DELTHYRIS. Dalman. _Fam._ Brachiopoda, Lam.--_Descr._ Hinge more or
less rounded, with distant umbones; both valves convex; with the umbo
of the largest rostrated and deltoid, with a hollow. This genus forms
part of the genus Spirifer, Sow. Fig. 205. D. Plycotes, Dalman.

DELTOID. ([Greek: D], _delta_.) Triangular.

DENDOSTREA. Sw. ([Greek: Dendron], _dendron_, tree; [Greek: ostreon],
_ostreon_, oyster.) Ostrea _Crista-galli_, and other species which are
attached to stems of sea-weed and corallines, by means of arms thrown
out from the inner surface of the lower valve. Fig. 181, Ostrea Folium.

DENTALIUM. Auct. (_Dens_, a tooth.) _Fam._ Maldania, Lam. _Order_,
Cirrobranchiata, Bl.--_Descr._ Tubular, arched, increasing in size
towards the anterior extremity, open at both ends; small aperture
sometimes having a lateral fissure; large aperture round; external
surface ribbed, striated or smooth.--_Obs._ The well known shells
composing this genus are shaped very much like an elephant's tusk, and
are not liable to be confounded with any other genus. The fossil
species are sometimes termed Dentalithes, from _dens_, a tooth, and
_lithos_, a stone. The Dentalia, being true molluscs, are not rightly
placed among the Annelides. Fig. 2, D. octogonum. Found on sandy shores
in most climates.

DENTATED. Having teeth or raised points.

DENTICULATED. (Denticulatus, Lat.) Having little teeth or raised
points.

DEPRESSED. Flattened, pressed down, as the spires of some shells.

DEXTRAL Spiral Shells. Place the point of a spiral shell towards the
eye, with its mouth downwards; if, as in most instances, the aperture
be on the right side of the axis, it is a _dextral_ shell, if
otherwise, it is _sinistral_ or _reversed_. Balea (fig. 296), and
Clausilia (fig. 295), are examples of reversed shells.

DEXTRAL Valve. Take a bivalve shell closed, place it before the eye,
with the umbones uppermost, and the posterior side, which may be known
by the ligament towards the observer, whose right side will then
correspond with the right valve of the shell.

DIADEMA. Ranz. CORONULA Diadema, Auct. fig. 17.

DIANCHORA. Sow. _Fam._ Pectinides, Lam. _Order_, Palliobranchiata,
Bl.--_Descr._ Inequivalve, attached, oblique, subtriangular; attached
valve, having an opening in the place of the umbo; the other valve
auriculated, with an obtuse umbo; hinge without teeth.--_Obs._ The
green sand fossils contained in this genus differ from Plagiostoma in
being attached. Fig. 175, D. striata.

DIAPHANOUS. ([Greek: Dia], _dia_, through; [Greek: phainô], _phaino_,
to shine.) Transparent.

DIAPHRAGM, ([Greek: diaphragma], a partition.) This term is applied to
the septa, by which the chambers of multilocular and other shells are
divided from each other.

DICERAS. Lam. ([Greek: Dis], _dis_, double; [Greek: Keras], _ceras_,
horn.) _Fam._ Chamacea, Bl. and Lam.--_Descr._ Inequilateral,
inequivalve, attached by the point of the umbo of the larger valve;
umbones prominent, spirally twisted and grooved; hinge with one large
thick tooth in the larger valve; muscular impressions, two in each
valve.--_Obs._ The prominent spiral umbones, which give rise to the
name of this genus, with the circumstance of its being attached by the
point of one of them, is sufficient to distinguish it from any other,
although it appears to approach Isocardia in some characters. In others
it will be found still more nearly to resemble Chama. In fact, from
being attached and irregular, the shells composing this genus have been
considered as Chamæ with produced umbones. The singular fossil shells
composing this genus, are found in granular limestone, near Geneva and
in Normandy. Fig. 154, D. perversum.

DIDONTA. Schum. SAXICAVA. Auct.

DIFFUSE. (_Diffundo_, to spread out, to dilate.) A term applied to the
aperture of a univalve shell, when it is spread out or widened into a
flat surface, or digitations. _Alated_ is another term used to express
the same character. Thus, the shells belonging to the family of Alatæ,
in the system of Lamarck, are _diffuse_ in the outer lip. Fig. 402 to
406.

DIGITATED. (_Digitus_, finger.) Branched out in long points, as
Ricinula, fig. 413.

DILATED. Expanded, spread. This term has the same application as
diffuse and alated, explained above. The outer lip of Rostellaria
Columbaria, fig. 403 (Hippochrenes, Montf.), will serve as an example.

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

DIMYARIA. ([Greek: Dis], _dis_, double; [Greek: muon], _myon_, muscle.)
The first order of Conchifera, Lam. including those molluscs which have
two adductor muscles, and consequently two muscular impressions in each
valve. The Conchifera Dimyaria are divided into Crassipedes,
Tenuipedes, Lamellipedes, and Ambiguæ, fig. 44 to 155.

DIOICA. Bl. The first division of the class Paracephalophora, Bl. It is
divided into the orders Siphonobranchiata and Asiphonibranchiata, Bl.

DIPLODON. Spix. HYRIA Syrmatophora, Lam. fig. 144, and UNIO
multistriatus, Lea, are doubtfully quoted by Lea as belonging to this
apparently ill-defined genus of Nayades.

DIPSAS. Leach. A genus or sub-genus of Nayades, the distinctive
character of which is "having a linear tooth under the dorsal edge." D.
plicatus, fig. 142.

DISCINA. Lam. ORBICULA, Auct.

DISCODOMA. Sw. A sub-genus of Lucerninæ, Sw. (Helix), thus described,
"teeth none; aperture angulated; the inner lip nearly obsolete; the
outer only slightly thickened; margin carinated."

DISCOIDAL. (_Discus_, a circular plane.) A spiral shell is said to be
discoidal, when the whorls are so horizontally convolute as to form a
flattened spire. _Ex._ Planorbis, fig. 311. Orbulites Discus, fig. 479.

DISCOLITES. Montf. A genus of microscopic Foraminifera.

DISCONTINUOUS. Interrupted. _Ex._ The siphon of Nautilus is
discontinuous, i. e. its termination in one chamber does not reach to
its commencement in the next. The varices of Triton, occurring in
different parts of the whorls, do not form the continuous ridges which
characterize the generality of the Ranellæ.

DISCORBITES. Lam. A genus of microscopic Foraminifera.

DISTANT. The teeth on the hinge of a bivalve shell are said to be
distant when they are remote from the umbones.

DIVARICATED. Diverging, meeting in a point, as the teeth on the hinge
of Placuna, fig. 184.

DOLABELLA. Lam. (Dim. from _Dolabra_, a hatchet.) _Fam._ Aplysiacea,
Lam. and Bl.--_Descr._ Hatchet-shaped, arched, covered with a horny
epidermis; posteriorly attenuated, thickened, sub-spiral, anteriorly
plane, broad, thin; posterior margin reflected.--_Obs._ The two or
three species of Dolabella known are inhabitants of the Indian Ocean.
They were placed by Linnæus in his very convenient genus Bulla, under
the name B. dubia. Fig. 255, Dolabella Rumphii.

DOLIUM. D'Argenville. (_a tun._) _Fam._ Purpurifera, Lam.
Entomostomata, Bl.--_Descr._ Thin, ventricose, oval, or globular, with
a short spire; large aperture terminating in a reflected canal, and
spirally ribbed or grooved external surface; outer lip crenated; inner
lip reflected over part of the body whorl, which terminates in a tumid
varix; epidermis light, horny. Mediterranean and East Indian.--_Obs._
This genus is distinguished from Cassis by the outer lip, which is not
reflected. The species which are not so rotund as the others, as D.
Perdix, Auct. have been separated under the name Perdix, as generic.
Fig. 420, Dolium Maculatum.

DONAX. Auct. _Fam._ Nymphacea, Lam. Conchacea, Bl.--_Descr._ Equivalve,
inequilateral, trigonal, with the anterior side short, straight, plane;
the posterior side elongated, drawn to a narrow, rounded termination;
hinge with two cardinal teeth in one valve, one in the other, and one
or two, more or less remote lateral teeth; ligament external; muscular
impressions two in each valve; palleal impression sinuated
posteriorly.--_Obs._ The Capsæ have not the crenated margins, the short
anterior side, and the distinct lateral teeth, which characterize the
Donaces. Some species of Erycina resemble Donax in general form, but
are at once distinguished by the ligamentary pit in the hinge. Sandy
shores in all climates. Fig. 108, D. cuneatus.

DORSAL. A dorsal shell is one placed upon the back of the animal. The
dorsal margin of a bivalve shell is that on which the hinge is placed;
the opposite margins are termed ventral. The dorsal surface of a spiral
univalve is that which is seen when the aperture is turned from the
observer. The dorsal valve is the uppermost in Brachiopodous bivalves.
The dorsal part of a symmetrical convolute univalve, such as the
Nautilus and Ammonite is that part of the whorls which is at the
greatest distance from the spire, that is, the outer part of the
whorls. Thus the situation of the siphon is said to be dorsal when it
pierces the septum near the outer edge of the whorls. The dorsal part
of symmetrical conical univalves, such as Patella, is the upper part,
on which the apex is placed.

DORSALIA. Lam. (_Dorsum_, the back.) The first family of the order
Annelides Sedentaria, Lam. containing the genera Arenicola, not a
shell, and Siliquaria, fig. 1, which is now considered as a true
mollusc, and placed next to Vermetus.

DOSINA. Schum. VENUS Verrucosa, Casina, and similar species. Fig. 119,
a.

DREISSINA. MYTILUS Polymorphus. Auct. fig. 159. This genus differs from
Mytilus principally in the characters of the animal. The shell is
characterized by a small septiform plate under the hinge within.
Fluviatile, Europe and Africa.

EBURNA. Lam. (_Eburneus_, ivory.) _Fam._ Purpurifera, Lam.
Entomostomata, Bl.--_Descr._ Oval, thick, smooth, turrited,
umbilicated; spire angulated, acute, nearly as long as the aperture;
aperture oval, terminating anteriorly in a canal, posteriorly in a
groove; outer lip slightly thickened with an anterior notch, which
terminates in a spiral fold surrounding the body whorl; umbilicus
generally covered by the thickened columellar lip.--_Obs._ The
beautiful shells called ivory shells, which originally constituted part
of this genus, are now placed in the genus Ancillaria by authors. They
differ from the present genus Eburna, in having the sutures of the
spire covered with a polished enamel. (A. glabrata, fig. 455.) The
Eburnæ resemble in some respects the genus Buccinum, but a glance at
the figure will enable the reader to distinguish a true Eburna from all
other shells. Fig. 426 is Eburna Zeylanica. A catalogue of 9 species is
given in part 20 of the Conchological Illustrations published by the
Author, accompanied by figures of several species.

ECHIDNIS. Montf. Described as a straight, chambered, annulated, fossil
shell, computed from the extremely gradual increase in diameter of the
fragments to be at least sixteen feet long. Found in marble from the
Pyrenees.

ECHINELLA. Sw. A sub-genus of Monodonta. Sw. Malac. page 352.

EFFUSE. (_effundo_, to pour out.) The aperture of an univalve shell is
said to be effuse when there is a notch in the margin which would
suffer a liquid to escape, and thus prevent it being filled to the
brim.

EGEON. Montf. A genus of microscopic Foraminifera.

EGERIA. Lea. (Contrib. to Geol. p. 49, pl. 1.) A genus of fossil
bivalves, described as very variable in form, with or without lateral
teeth, sometimes a crenated margin, &c. The only certain characters
appear to be that they have two diverging cardinal teeth in each valve,
one of which is bifid; and an external ligament. Lea states that the
Egeriæ should be placed between the Sanguinolariæ and the Psammobiæ,
which two latter genera have been united by Sowerby. Fig. 103, E.
Triangulata, from the tertiary formation of Alabama.

ELENCHUS. Humph. A genus composed of TROCHUS Iris, Auct. and other
similarly formed species. It is the same as CANTHARIDUS of Montfort.

ELEPHANT'S TUSK. The common name given by dealers to shells of the
genus Dentalium. _Ex._ D. octogonum, fig. 2.

ELEVATED. A term which is applied by some conchological writers to the
spire of an univalve shell when it consists of numerous whorls drawn
out into a telescopic form. Other authors use the term _elongated_, or
the more simple one '_long_,' to express the degree of elevation.

ELISMA. Leach. A sub-genus of Bulinus. B. acutus, Auct. Gray, Turton,
p. 185.

ELLIPSOLITHES. Montf. ([Greek: Elleipsis], _ellipsis_, oval; [Greek:
lithos,] _lithos_, stone.) A genus composed of Ammonites, which instead
of being regularly orbicular, take an elliptical or oval form. This
character appears to be accidental, as some individuals of the same
species, both of Nautilus and Ammonites, are round, while others are
compressed into an oval form.

ELLIPSOSTOMATA. Bl. ([Greek: Elleipsis], _ellipsis_, oval; [Greek:
stôma], _mouth_.) The third family of the class Asiphonibranchiata, Bl.
The shells of this family are described as of various forms, generally
smooth; the aperture longitudinally or transversely oval, completely
closed by a horny or shelly operculum. This family contains the genera
Rissoa, Phasianella, Ampullaria, Helicina, and Pleuroceras.

ELLIPTICAL. ([Greek: Elleipsis], _ellipsis_.) Oval. Applied to any
shell or part of a shell, having that form.

ELMINEUS. Leach. _Order_, Sessile Cirripedes, Lam.--_Descr._ Four
unequal valves, arranged circularly side by side, forming a quadrate
cone; aperture large, sub-quadrate, irregular; operculum composed of
four valves, in pairs.--_Obs._ This genus differs from Conia in the
structure of the shell, the latter being porous. Fig. 22, Elmineus
Leachii.

ELPHIDIUM. Montf. (Conch. Syst. t. 1. p. 15.) A genus of microscopic
Foraminifera.

EMARGINATED. (_e_, out; _margo_, border.) Notched or hollowed out.
Applied to the edges or margins of shells, when instead of being level
they are hollowed out, as the outer lip of Oliva, fig. 457, at the
base, and the ventral margins of some bivalves.

EMARGINULA. Lam. (_e_, out; _margo_, border.) _Fam._ Calyptracea, Lam.
Branchifera, Bl.--_Descr._ Patelliform, oblong or oval; anterior margin
notched or emarginated; apex posteriorly inclined; muscular impressions
wide.--_Obs._ Emarginula elongata, of some Authors, PARMOPHORUS of De
Blainville is commonly called the Duck's bill limpet, from its shape.
The Emarginulæ may be known from Patellæ and other neighbouring genera,
by the notch or slit in the anterior edge. In the genus Rimula, Defr.
fig. 243, this slit is near the apex, and does not reach the margin.
Recent species occur in all climates, but are not numerous. Fossil
species are still more rare, occurring in the Calc-grossièr, Crag and
Oolite. E. fissurata, fig. 241.

ENA. Leach. A sub-genus of Bulinus. B. Lackhamensis. Mont.

ENDOSIPHONITES. A genus composed of Ammonites, having the siphon close
to the body whorl, fig. 476.

ENDOTOMA. Rafinesque. A genus of microscopic Foraminifera.

ENROULEES. Lam. See CONVOLUTÆ.

ENSATELLA. Sw. A genus consisting of SOLEN ensis, Auct. fig. 60, and
other species similarly curved. _Genus_ ENSIS, Schum.

ENSIS. Schum. SOLEN ensis, Auct. and similar species.

ENTALIS. Defr. DENTALIUM duplicatum, Bl. PHARETRIUM, König. This genus
is described as a small tube, within a larger one, the smaller
extremity of the inner tube projecting beyond that of the outer one.
Deshayes, who describes this genus, expresses a conviction that the
soft parts of the animal must be entirely different from those of the
animal of Dentalium. The genus PHARETRIUM, as described by König in his
"Icones Fossilium Sectiles," is evidently identical with Entalis. It is
placed by him in the family of Pteropoda, but being a fossil shell,
there is some difficulty in finding its place in the system. See
plates, fig. 3.

ENTELLITES. Fischer. A genus composed of species of TEREBRATULA,
SPIRIFER, and PRODUCTUS, Auct. having the hinge large and the umbones
short. ORTHIS? Dalman.

ENTIRE. (Integra.) Not interrupted, not emarginated. The peritrême of a
univalve shell is said to be entire when not interrupted by canals or
by the body whorl. _Ex._ Cyclostoma, fig. 304. The palleal impression
is entire, when continued without interruption, or without a sinus.

ENTOMOSTOMATA. Bl. The second family of the order Siphonibranchiata,
Bl. The shells of this family are described as differing but little
from those contained in the family of Siphonostomata of the same
author, both with regard to the soft parts, and their testaceous
covering. This family partly answers to the Purpuriferæ in the system
of Lamarck, and contains the genera Subula, Cerithium, Melanopsis,
Planaxis, Terebra, Eburna, Buccinum, Harpa, Dolium, Cassidaria, Cassis,
Ricinula, Cancellaria, Purpura, Concholepas.

EOLIDES. Montf. A genus of microscopic Foraminifera.

EPIDERMIS. ([Greek: Epi], _epi_, over or upon; [Greek: derma], _derma_,
skin.) The fibrous, horny, external coating of shells, called by the
French, "_Drap marin_," or marine cloth. Lamarck objects to the name
Epidermis because he does not consider the substance as answering to
the cuticle or scarf skin of the human body, but more analogous to the
nails and hair. Gray calls it the PERIOSTRACUM, from the membranous
skin covering the bones of quadrupeds.

EPIPHRAGM. The membranaceous or calcareous substance by which some
species of molluscs close the aperture of the shell, when they retire
within it to hibernate. When the animal wishes to come forth from his
hiding-place, again to breathe the air, the edges of the Epiphragm are
detached by a chemical process, so that it drops off. The name
Hibernaculum has also been given to this covering. It must not be
confounded with the operculum, which is a permanent portion of the
shell, and is used as a door, fitted to the foot of the animal and
moved at will to open or close the aperture of the shell, whereas the
Epiphragm is produced for the occasion from a mucous secretion of the
animal and dissolved at the edges when no longer wanted, when it drops
off.

EPISTYLA. Sw. A subgenus of the genus HELIX. E. conical. Sw. Helix
Epistylium, fig. 281.

EPONIDES. Montf. A genus of microscopic Foraminifera.

EQUILATERAL. (Æquus, equal; latus, side.) Equal-sided. A term applied
to bivalve shells, when a line drawn down perpendicularly from the apex
would divide the shell into two equal parts. _Ex._ Pectunculus pilosus,
fig. 134.

EQUIVALVE. (Æquus, equal; _valva_, a valve.) A term applied to a
bivalve shell when the valves are equal to each other in dimensions.

ERATO. Risso. _Fam._ Convolutæ, Lam.--_Descr._ Ovate, more or less
angulated, smooth or granulated, with a dorsal scar; spire short;
aperture large, angulated, emarginated; columella slightly crenated;
outer lip reflected, denticulated on the inner edge. Suture of the
whorls covered with enamel.--_Obs._ This genus of shells resembles
Marginella in form, but has no folds on the columella. Having a scar or
groove down the back it may be considered intermediate between
Marginella and Cypræa. Fig. 454, E. Maugeriæ. In the Author's
Conchological Illustrations, seven species are enumerated and figured.

ERUCA. Sw. A subgenus of Clausilia. Sw. Malac. p. 334.

ERVILIA. Turt. A genus described as "oval, equivalve, equilateral,
closed. Hinge with a single erect tooth closing between two small
diverging ones in the opposite valve: lateral teeth none. Ligament
internal. E. nitens. Turt. Mya. nitens, Auct."

ERYCINA. Lam. _Fam._ Mactracea, Lam. Conchacea, Bl.--_Descr._ Ovate or
triangular, transverse, equivalve, inequilateral, smooth; hinge with a
ligamentary pit, two diverging cardinal and two lateral teeth in each
valve; muscular impressions two in each valve; palleal impressions
sinuated. East and West Indies and Mediterranean.--_Obs._ This genus is
distinguished from _Mactra_ and _Lutraria_ by the cardinal teeth being
placed one on each side of the ligamentiferous pit; whereas in the last
named genera they are both placed on the anterior side. Fig. 86, E.
Plebeja.

ERYTHRÆA. The ancient name for CYPRÆA.

ESCUTCHEON. The impression on the posterior dorsal margin of some
bivalve shells. That on the anterior margin is named the lunule. The
escutcheon is pointed out by the letter _e_ in some of the figures of
Cythereæ. Fig. 117, _a. b. c._

ETHERIA. Lam. (_Æther_, air.) Fam. Chamacea, Lam. and Bl.--_Descr._
Irregular, inequivalve, inequilateral, foliaceous, pearly within,
covered by an olive green epidermis without; hinge callous, undulated,
destitute of teeth; ligament partly external, partly internal, passing
through the hinge on a somewhat raised, callous area in the lower
valve. Muscular impressions elongated, two in each valve, united by a
slender palleal impression. Rivers of Africa.--_Obs._ The irregular,
unequal air-bubbles of the inner surface, whence this genus derives its
name, are very brilliant in some species, and atone, in some measure,
for the rugged ugliness of the exterior. In its irregular form,
foliated structure, and toothless hinge, it resembles OSTREA, from
which it differs in having two muscular impressions. Fig. 155, E.
semilunata.

EULIMA. Risso. _Fam._ Scalariens, Lam.--_Descr._ Elongated, smooth,
pyramidal; spire long, composed of numerous whorls; apex acute,
slightly tortuous; aperture oval, rounded anteriorly, acute at the
posterior union with the body whorl; outer lip slightly thickened;
columella smooth. Fig. 347, E. labiosa, fig. 348, E. splendidula. A
complete illustrated monograph of this genus of pretty shining little
shells, consisting of 15 known species, is given in parts 52 and 53 of
the Conchological Illustrations by the author.

EUOMPHALUS. Sow. _Fam._ Scalariens, Lam.--_Descr._ Orbicular,
planorbular spire, with three or four volutions, imbricated above;
smooth below; aperture of a round polygonal form; umbilicus large,
penetrating to the apex of the shell.--_Obs._ This genus of fossils
very nearly resembles Delphinula. The main difference appears to be
that the whorls do not increase so rapidly in size in the former as in
the latter. Fossil, in the Carboniferous Limestone. Fig. 350.

EXOGYRA. Sow. A genus of fossil bivalves, resembling Chama in shape and
Ostræa in structure, having but one muscular impression in each valve.
Fig. 183.

EXSERTED. Standing out, protruding.

EXTERNAL. An external shell is one which contains the animal, and is
not covered by the mantle.

FASCIATED. (_fascia_, a band.) Banded or striped. Ex. Carocolla
marginata, fig. 277.

FASCICULATED. (from fasciculum.) A little bunch of hairs or bristles
against each end of each valve, characterizes some species of the genus
Chiton, which are termed fasciculated species.

FASCIOLARIA. Lam. _Fam._ Canalifera, Lam. Siphonostomata, Bl.--_Descr._
Elongated, fusiform, ventricose; spire conical, consisting of few
rounded or angulated whorls; aperture wide, terminating in a long
straight open canal: columella lip with several oblique folds, the
lower of which is larger than the rest; operculum horny,
pyriform.--_Obs._ This genus is known from Fusus by the folds on the
columella; from Turbinella, by their obliquity and the last being
larger than the rest. Fig. 386, F. Trapezium. East and West Indies and
Australia.

FAUNUS. Montf. MELANOPSIS, Auct.

FERRUGINEOUS. Of an iron rust colour.

FERUSSINA. Grateloup. STROPHOSTOMA, Deshayes.

FIBROUS. A shell is said to be of a fibrous structure when a fracture
would present a series of perpendicular fibres, as Pinna.

FICULA. Sw. A generic group of shells, consisting of those species of
PYRULA, Auct. which have the true pear-shaped character. Fig. 390, P.
Ficus. Sowerby confines the name Pyrula to these species.

FIMBRIA. Megerle. CORBIS, Lam.

FIMBRIATED. Fringed; as Murex fimbriatus, a delicate white species,
with broad fringed varices.

FISSURE. (_Fissura_, a slit.) A slit or cut, a narrow perforation, as
in Emarginula and Fissurella.

FISSURELLA. Brug. (_Fissura_, a fissure.) _Fam._ Calyptracia, Lam.
Branchifera, Bl.--_Descr._ Patelliform, oval or oblong, radiated; apex
anterior, perforated.--_Obs._ The Fissurellæ are known from Patellæ by
the perforation in the apex. Fig. 245. The catalogue published by the
author in the Conchological Illustrations, enumerates 68 species.

FISTULANA. Lam. (_Fistula_, a pipe.) _Fam._ Tubicolæ, Lam. Adesmacea,
Bl.--_Descr._ A transversely elongated, equivalve, inequilateral
bivalve, enclosed by a septum within the widest, closed extremity of a
straight calcareous tube. Fistulana is known from Gastrochæna by the
straightness of the tubes, and the oblong state of the valves. Fig. 54,
Fistulana Clava.

FLEXUOUS. Having windings or bendings. _Ex._ The Tellinæ are known by
the twist or flexuosity in the posterior ventral margin of the shell.

FLORILLUS. Montf. A genus of microscopic Foraminifera.

FLUVIATILE. (Fluviatilis.) Belonging to a river or running stream.
_Ex._ Limnæa fluviatilis.

FLUVIATILE CONCHACEA. See CONCHACEA.

FOLIATED, or FOLIACEOUS. (From _folium_, a leaf.) When the edges of the
successive layers of which a shell is composed are not compacted but
placed apart from each other, projecting like tiles, the shell is said
to be of a foliated structure. The common Oyster, fig. 180, presents a
familiar example.

FORAMINIFERA. D'Orb. (_Foramen_, a hole or pit.) An order established
for minute many chambered internal shells, which have no open chamber
beyond the last partition. Lamarck, D'Orbigny, and other writers have
placed them among the Cephalopoda in their systems, but Du Jardin, on
comparing the fossils with some recent species of the same class,
arrived at the conclusion, now generally adopted, that they constitute
a distinct class, much lower in degree of organization than even the
Radiata. Not recognizing these microscopic bodies as shells, properly
so called, but considering them sufficiently numerous and interesting
to form a distinct branch of study, I do not think it desirable to
describe the genera, or to present any arrangement of them in this
work.

FORNICATED. Arched or vaulted, as the exfoliations on the costæ of
Tridacna Elongata, fig. 157.

FOSSIL SHELL. A shell is considered to be in a fossil state when, the
soft parts having ceased to exist, it is deprived of all its animal
juices, has lost all, or nearly all its natural colour, and is thus
changed in its chemical composition, when little or nothing is left but
a mere bone, which is embedded in a sedimentary deposit. In this state,
it is fragile, prehensile to the tongue, and either destitute of colour
or tinged with the diluted mineral matters which pervade the stratum in
which it lies. In some cases, the mineral composition of the shell is
so completely changed as no longer to present its proper structure,
consisting of successive oblique layers of shelly matter; but is
altered into a fibrous structure, composed of rhomboidal particles. An
example of this will be found in the Belemnites, which if broken, shew
the perpendicular fibres. In other cases, the matter which has entered
and filled up the cavities of the shell has become silicified, or
changed into flint, and the shell itself has been decomposed and fallen
off, so as to leave nothing but an external or internal cast of its
form, in flint. This is called a Conchyliomorphite by continental
writers. Some of the most important of Geological data are obtained by
a minute comparison of fossil shells, found in various beds, with
recent ones presenting the nearest resemblance to them. Some species of
fossil shells are considered as identical with recent species. And many
Geologists seek to fix the chronology of the different strata by the
number of species which they inclose bearing a resemblance to the
recent species. Indeed, all who would study Geology with success, will
find it indispensably necessary to obtain a thorough knowledge of
Conchology.

FRAGELLA. Sw. A sub-genus of Monodonta, corresponding with the genus
Clanculus, Montf. consisting of M. Pharaonis (fig. 361), and similar
species. Sw. p. 352.

FRAGILE. (_Fragilis._) Tender, easily broken.

FREE SHELL. One that is not attached.

FREE VALVE. In attached bivalve shells, one only is fixed; the other is
then _free_, as far as to the action of opening and shutting.

FRESH-WATER SHELLS, (sometimes described as aquatic) are those which
either inhabit rivers, running pools and ditches, in which case they
are _fluviatile_; or wells and ponds of standing water, &c. Fresh-water
shells are either thin and horny in their texture, as the Limneana of
Lamarck; or are covered with a compact, smooth, horny epidermis. They
are generally simple in form, subject to corrosion where the epidermis
is wounded or broken, and are circumscribed with regard to the classes
and genera to which they belong. The family of Nayades includes nearly
all the fresh-water bivalves; and the Melaniana and Limneana are the
principal among univalves.

FRONDICULARIA. Defr. A genus of microscopic Foraminifera.

FRONT. The surface of a shell on which the aperture appears.

FULCRUM. That part of a shell on which any other part rests or turns.
The term is applied more particularly to the tumid part in the hinge of
bivalve shells on which the ligament is fixed.

FULGUR. Montf. PYRULA perversa, Auct. and such other species as have an
angulated spire. Fig. 388.

FUSIFORM. (_Fusus_, a spindle.) Shaped like a spindle, swelling in the
centre and tapering at the extremities. _Ex._ Fusus, fig. 387.

FUSUS. Brug. (A spindle.) _Fam._ Canalifera, Lam. Siphonostomata,
Bl.--_Descr._ Fusiform, turrited, with many rounded whorls; aperture
generally oval, terminating in a long straight canal; operculum horny,
pyriform.--_Obs._ The Fusi are subject to considerable variations in
form. The recent species are numerous and do not appear to be confined
to any climate. The fossil species are also numerous, chiefly abounding
in the tertiary formations. The recent species are mostly tropical.
Fig. 387, F. Colus.

GALATHÆA. Brug. POTAMOPHILA, Sow. MEGADESMA, Bowd.

GALEA. Klein. PURPURA, Auct.

GALEOLARIA. Lam. (From Galea, a helmet or crest.) A genus composed of
species of SERPULA, Auct. Distinguished as being fixed by the side of
the shell, and having the anterior extremity erect, the aperture
terminating in a tongue-shaped projection.--_Obs._ This genus is said
by Lamarck to resemble Vermilia in other respects, but to differ in
having the anterior part raised. Fig. 6, G. decumbens. Africa and
Australia.

GALEOMMA. Turt. _Fam._ PHOLADARIA, Lam.--_Descr._ Thin, oval,
equivalve, equilateral, with the ventral margin gaping; hinge with one
cardinal tooth in each valve; muscular impressions two, approximate;
palleal impression interrupted, not sinuated; ligament small, partly
internal, partly external, fixed on a prominent fulcrum.--_Obs._ The
wide hiatus in the ventral margins of this equilateral shell prevents
the possibility of confounding it with any other. Four or five recent
species are known, one of which is found on the coast of Sicily, and
also in the British Channel. G. Turtoni, fig. 58.

GALERICULUS. (_Galericulum_, a little cap or bonnet.) VELUTINA, Auct.
fig. 337.

GALERUS. Humph. CALYPTRÆA, Lam.

GAPING. (_Hians._) Bivalve shells are said to gape when the margins do
not meet all round. _Ex._ Gastrochæna, fig. 52.

GARI. Schum. PSAMMOBIA, Lam.