A Conchological Manual, George Brettingham Sowerby [little readers .TXT] 📗

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.

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:--

 

CONULARIA. Conical, externally striated; no siphon. Fig. 469.

 

AMPLEXUS. Cylindrical; margins of the septa reflected. Fig. 463.

 

ORTHOCERATITES. Straight, gradually conical; septa simple;

       siphon central. Fig. 464.

 

NODOSARIA. Divided externally into lobes. Fig. 465.

 

BELEMNITES. Straight, conical; septa simple; siphon lateral;

       apex solid; internal cast, or nucleus, pyramidal, separable. Fig.

       466 to 468.

 

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:--

 

PEDUM. Flat, turned up at the sides, an hiatus for the passage

       of a byssus. A triangular disc on the hinge. Fig. 179.

 

OSTREA. Foliaceous, irregular, hinge on a small triangular disc.

       Including Dendostrea, Ostræa, Exogyra, Gryphæa. Fig. 180 to 183.

 

PLACUNA. Two diverging ribs near the umbones. Fig. 184.

 

PLACUNANOMIA. The same, but attached by fibres passing through a

       hole in one valve. Fig. 189 to 191.

 

ANOMIA. No costæ, attached by a bony substance passing through a

       hole in one valve. Fig. 186 to 188.

 

VULSELLA. Tongue-shaped, a ligamentary pit on the hinge. Fig.

       185.

 

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,

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.

 

   OTION. Leach. ([Greek: ôtion], a little ear.) _Order._ Pedunculated

   Cirripedes, Lam.--_Descr._ Body sub-quadrate, supported on a fleshy

   pedicle with a gaping aperture and two posterior auricular tubes;

   valves five, separate, two semilunar, placed at the sides of the

   aperture, two terminal, very small, one dorsal, minute.--_Obs._ Otion

   differs from Cineras in having two cylindrical posterior tubes, and in

   the extreme minuteness of three out of five of the valves. Found on

   spars floating in the sea, &c. O. Cuvierii, (Lepas aurita, Linn.) Fig.

   43, O. Cuvieri.

 

   OTIS. Humph. AURICULA, Lam.

 

   OVATE. (_Ovatus._) Egg-shaped or oval.

 

   OVEOLITHES. Montf. A microscopic shell resembling Bulla.

 

   OVIPAROUS MOLLUSCA. Those which produce their young in eggs. Used in

   distinction from the VIVIPAROUS MOLLUSCA, whose young are perfectly

   formed before they leave the body of the parent.

 

   OUTER LIP. See LABRUM.

 

   OVULUM. Brug. (_Ovum_, an egg, dim.) _Fam._ Convoluta, Lam.

   Angyostomata, Bl.--_Descr._ Ovate or fusiform, smooth, convolute, spire

   covered; aperture narrow, with a canal at each extremity; outer lip

   crenulated, inflected; inner lip smooth, callous towards the spiral

   extremity; dorsal area wide, sometimes indistinctly marked.--_Obs._ The

   Ovula were placed by Linnæus in his genus Bulla, from which they are

   very remote. They differ from Cypræa in having the inner lip