Part 31

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.