CIONELLA. Jeffreys. _Fam._ Colimacea, Lam.--_Descr._ Oblong or elongated; last whorl large; apex rather acute; columella, sub-interrupted; aperture canaliculated, sub-effuse at the base; margins very unequal; no umbilicus. BULINUS octonus, lubricus, acicula, &c. Auct. C. lubrica, fig. 285. CIRCE. Schum. VENUS castrensis, fig. 117 d. V. sulcatina, arabica, pectinata, Auct. and other similar species. CIRRIPEDES. Lam. The tenth class of invertebrated animals, so named from the curled and ciliated branchia which protrude from the oval aperture of the shells. The class Cirripedes of Lamarck constitutes the entire genus _Lepas_ of Linnæus. They are divided into two sections; first, Sessile Cirr. attached by the basal portion of the shell; second, Pedunculated Cirr. supported upon a Peduncle. Figs. 14 to 45. CIRROBRANCHIATA. Bl. The first order of Paracephalophora Hermaphrodita, Bl. This order has been formed for the purpose of giving a place in the system to the genus Dentalium. The animal of which has lungs, consisting of numerous filaments, having their basal origin in two radical lobes under the neck. CIRRUS. J. Sowerby (cirrus, a tendril.) _Fam._ Turbinacea, Bl. and Lam.--_Descr._ Spiral, conical, with a hollow axis; whorls contiguous, numerous, rounded, or slightly angulated.--_Obs._ This fossil genus resembles Trochus, from which it is known by the deep funnel-shaped umbilicus. Fig. 349, C. nodosus. CISTULA. Humph. CYCLOSTOMA, Lam. CLANCULUS. Montf. TROCHUS _Pharaonis_, Lam.--_Obs._ This, with several other species, belong more properly to MONODONTA, Lam. ODONTIS, Sow. Fig. 361. CLATHODON. Conrad. GNATHODON, Gray. CLAUSILIA. Drap. (_Clausium_, a valve or folding door.) _Fam._ Colimacea, Lam. Limacinea, Bl.--_Descr._ Spire elongated, consisting of many volutions; aperture small, sub quadrate, having several tooth-shaped folds on the columella. A small, elastic, shelly plate, attached to the columella within, called the Clausium, its office being to enclose the aperture when the animal has retired within the shell.--_Obs._ This last character distinguishes it from the Pupæ, to some of which it bears a very near resemblance. _Hab._ Land, in the central and southern parts of Europe, several British species. Fig. 295, C. Macascarensis. CLAUSIUM. A name applied to the beautiful contrivance whence the genus Clausilia derives its name, consisting of a little bony tortuous plate, placed in a groove on the columella. Here it serves the purpose of a door, which, when not prevented by counteracting pressure, springs forward on its elastic ligament, and encloses the animal in his retirement. The aperture is opened by pushing back the clausium into the groove. CLAUSULUS. Montf. Conch. Syst. 1, 179. A genus of microscopic Foraminifera.