A Conchological Manual by George Brettingham Sowerby (best interesting books to read txt) 📕

   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,

   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