CYTHEREA. 135 



prinse belong to the Northern hemisphere. The recent species 

 are not numerous. Fossil species are found in the tertiary de- 

 posits. Cyprina may be known from Venus by the remote lateral 

 tooth and the thick epidermis. C. vulgaris, fig. 116. 



CYRENA. Auct. Fam. Fluviatile Conchaceae, 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 impres- 

 sion 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. (Kvprog, 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 r exporrecta, 

 Nonnull.) fig. 204. 



CYTHEREA. Lam. Fam. " Conques Marines," Lam.— Descr. 

 Equivalve, inequilateral, oval, lenticular, or sub-trigonal ; hinge 

 with two or more short, diverging cardinal teeth, and one an- 

 terior approximate lateral tooth in each valve. — Obs. The Cy- 

 therese are distinguished from the Veneres by the lateral tooth. 

 C. Meretrix, fig. 117, and 117, a. b. c. d. 



