CASSIS. (A helmet.) _Fam._ Purpurifera, Lam. Entomostomata, Bl.--_Descr._ Oval or triangular, ventricose, thick, generally tuberculated, with a short varicose spire; aperture long, sometimes narrow, with the outer lip thickened and reflected, generally denticulated; the inner lip spread over the surface of the body whorl, indented and incrassated at its inner edge; canal turned suddenly over the back of the shell. _Hab._ Seas of tropical climates. The fossil species are rare, occurring in the tertiary strata.--_Obs._ The large, common species of this well known genus are used for shell cameos and as ornaments on chimney pieces, grottos, &c. and are remarkable for the triangular disc, presented by the inner lip, which, in many species, is thickened and spread over the front of the body whorl and the angulated outer lip. The smaller, more rounded species, which have widened apertures, have been separated by Swainson, under the generic name CASSIDEA. The C. rufa, coarctata, &c. are formed by Mr. Stutchbury into a new genus under the name CYPRÆCASSIS, for reasons which will be stated under the word. Cassidaria is distinguished by the gradual curve of the canal. Fig. 410 is Cassis tuberosa, diminished. CASTALIA. Lam. _Fam._ Trigonées, Lam.--_Descr._ Fluviatile, equivalve, inequilateral, trigonal, with corroded umbones; hinge with two laminar, transversely striated teeth, one of which is posterior, remote from the umbones, short, divided, the other anterior, elongated; epidermis thick; internal surface pearly. Lamarck, in describing this shell, states, that he regards it as intermediate between Trigonia and Unio. It should, however, certainly have been placed in the family of "Nayades," and perhaps should form a part of the genus UNIO itself. C. ambigua, Lam. fig. 140. South America. CATILLUS. Brong. (A little dish.) INOCERAMUS, Sow. CATOPHRAGMUS. Sow. (From [Greek: Katô], _beneath_; [Greek: phragmos] _a place_ _paled in_.) _Order_, Sessile Cirripedes, Lam.--_Descr._ Light principal valves, cemented side by side in a circle; eight small pointed valves beneath, covering the joints of the upper circle, and numerous still smaller valves forming the base of the shell; operculum, four valves.--_Obs._ This is the only genus of Sessile Cirripedes, consisting of eight principal valves, excepting Octomeris, which is destitute of the accessary pieces from which the genus derives its name. Fig. 23. C. imbricatus. South Africa. CAUDAL CANAL. The elongated hollow process which terminates the aperture anteriorly of some univalve shells. For instance, Murex Haustellum, fig. 396, has an elongated caudal canal. CELLANTHUS. Montf. VORTICIALIS, Bl. A genus of microscopic Foraminifera.