Part 26

1. CYCLOSTOMA. Aperture round; operculum spiral. Fig. 303, 304.

2. NEMATURA. Last whorl contracted; operculum spiral. Fig. 305.

3. HELICINA. Aperture semi-lunar or angulated; operculum concentric. Fig. 306, 307.

4. PUPINA. Shell polished; operculum concentric; aperture round. Fig. 524.

5. STROPHOSTOMA. Aperture turned up towards the spire, like Anostoma, but said to have an operculum. Only known fossil. Fig. 97.

COLUMBELLA. Auct. (Columba, a dove.) Fam. Columellata, Lam.--Descr. Thick, oval, or angular; with short spire, and long narrow aperture, contracted in the centre, and terminating in a short canal; outer lip thickened and dentated; inner lip irregularly crenated. Epidermis thin, brown. Operculum very small, horny.--Obs. Those species of Mitra, which resemble Columbella in shape, may easily be distinguished by the plaits on the columella. The Columbellæ are marine, and few fossil species are known. Fig. 430, C. Mercatoria. Swainson has divided this genus into the following: Columbella, consisting of C. Mercatoria, &c.; Pusiostoma, consisting of the Strombiform species; Crassispira, which is most probably a Cerithium; Nitidella, consisting of the smooth species; Conidea, consisting of the more conical species; another set of the more conical species has been removed from this family, and placed in that of the "Coninæ," but as they are separated by no essential character, we suppose this has merely been done for the purpose of completing the "circle" of the last mentioned family, which otherwise would not have reached the required number of five. Mediterranean, East and West Indies, South America, Coast of California, Gallapagos, &c.

COLUMELLA. A solid column formed by the inner sides of the volutions of a spiral univalve. It is sometimes described as the inner lip of the aperture, of which it forms a part; but the term would be more properly confined to that portion of the inner lip which is seen below the body whorl, over which the remainder of the lip is frequently spread. All the inner edge of the aperture, including that part of it which covers the body whorl, is called the columellar lip. In fig. 431, the anterior termination of the columella is indicated by the letter c. The axis, is an imaginary line drawn strictly through the centre of the whorls, whether their inner edges form a solid column or not.

COLUMELLAR LIP. The inner lip. See COLUMELLA.

COLUMELLATA. Lam. A family of the order Trachelipoda, Lam. containing the following genera:--

1. MITRA. Elongated; aperture narrow; strong folds on the columella; including Mitrella, Mitreola, Tiara, and Conohelix. Fig. 431, 432.

2. MARGINELLA. Outer lip reflected; including Volutella, Persicula, Gibberula, and Glabella. Fig. 437.

3. COLUMBELLA. Outer and inner lips denticulated or granulated. Fig. 430.

4. VOLUTA. Outer lip thickened; folds on the columella; aperture generally wide; apex papillary; including Scaphella, Harpula, Volutilithes, Cymbiola. Fig. 433, 436.

5. MELO. Shell comparatively light; spire short, sometimes hidden; apex round, spiral; folds on the columella laminar. Fig. 435.

6. CYMBA. Upper edge of the aperture separated from the body whorl by a flat disc; apex mammillated, irregular; folds on the columella. Fig. 434.

7. VOLVARIA. Cylindrical; aperture long, narrow; folds on the columella; spire hidden. Fig. 439.

COLUS. Humphrey. FUSUS, Lam.

COMPLANARIA. Sw. A subgenus of ALASMODON (Unio), thus described, "shell winged; the valves connate; the bosses very small and depressed; cardinal teeth two or three; lateral teeth represented by irregular grooves. C. gigas (Unio), Sow. Man. fig. 141. Alasmodon complanatus, Say. C. rugosa, Sw."

COMPRESSED. Pressed together, or flattened. The application is the same as in common use. A Patella may be described as a vertically compressed cone. A Ranella, on account of the two rows of varices skirting the whorls, appears, as it were, laterally compressed. A bivalve shell is said to be compressed when it is flat, that is, when but a small cavity is left in the deepest part when the valves are closed. Perhaps the Placuna placenta, fig. 184, is the most remarkable instance of this.

CONCAMERATIONS. (Con, with, camera, a chamber.) A series of Chambers joining each other, as in Nautilus, Spirula, &c.

CONCENTRIC. A term applied to the direction taken by the lines of growth in spiral and other shells, (longitudinal of some authors.) Every fresh layer of shelly matter forms a new circle round an imaginary line, drawn through the centre of the spiral cone, down from the nucleus. When the edges of the successive layers are marked by any external characters, the shell is said to be concentrically striated, banded, grooved, costated, &c. A fine illustration of the latter is to be seen in the Scalaria or Wentletrap, fig. 351, Lines, bands, ribs, &c. in the opposite direction, (transverse of some authors,) are "radiating" in bivalves, as the ribs of Cardium, fig. 123, and "spiral" in univalves, that is, following the direction of the whorls, as the bands of colour in Pyramidella, fig. 342.

CONCHACEA. Bl. The eighth family of the order Lamellibranchiata, Bl. The shells are described as follows: nearly always regular, valves closed all round; apices curved towards the anterior; dorsal hinge complete, with teeth and ligament; the latter external or internal, short and thick; two distinct muscular impressions, united at the lower part by a parallel impression, which is frequently sinuated at the posterior. The genera described in this family are divided into three sections. First, those which are regular, and have distant lateral teeth, Cardium, Donax, Tellina, Lucina, Cyclas, Cyprina, Mactra, and Erycina. Second, those which are regular, and have no distant lateral teeth, Crassatella and Venus. Third, those which are irregular, Venerupis, Coralliophaga, Clotho, Corbula, Sphænia, and Ungulina.

CONCHACEA. Lam. A family of Lamarck's order Conchifera Dimyaria. Regular, unattached in general, closed at the sides. They are always more or less inequilateral. The Marine Conchacea are those which inhabit the sea. The fluviatile Conchacea are those which are found in rivers, ponds, &c. Each of these contain various genera, which may be arranged as follows:--

Fluviatile.

1. CYRENELLA. Three cardinal teeth; ligament long; shell thin. Fig. 114.

2. CYCLAS. Thin, oval; cardinal and lateral teeth; anterior side shortest, including Pera.

3. PISIDIUM. The same, with the posterior side shortest. Fig. 112.

4. CYRENA. Thick; cardinal and lateral teeth. Fig. 113.