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.