BIVALVIA. 207 



of Venus, which has the outer portion of a fibrous character, while in this it is more 

 compact, and in the recent shell is often enamelled. 



This genus is found extensively in the warmer regions of the globe ; as a fossil it 

 has been obtained very low in the secondary Formations, and was largely developed 

 during the early Tertiary Periods. 



1. CYTHEREA CHIONE, Linnceus. Tab. XX, fig. 4 a, b. 



CHAMA. Reyenfuss. Choix Coquil., p. 56, t. viii, fig. 17. 

 CURVIROSTRUM. Leigh. Nat. Hist. Chesh., p. 179, pi. iii, fig. 5, 1700. 

 VENUS CHIONE. Linn. Syst. Nat., ed. 12, p. 1131, No. 125, 1767. 



Poli. Test. Sicil., vol. ii, p. 85, pi. xx, figs. 1, 2, 1795. 

 Broc. Conch. Foss. Subap., p. 547, 1814. 

 Sismonda. Syn. Meth. Invert. Foss. Fed., p. 19, 1847. 



CHIONOIDES? Nyst. Coq. Foss. de Belg., p. 175, pi. xii, fig. 5 a, b, 1844. 

 PECTUNCULUS GLABER. Dacosta. Brit. Conch., p. 184, pi. xiv, fig. 7, 1778. 

 DIONE GLABER. Gray. List Brit. Moll., p. 6, 1851. 

 CYTHEREA CHIONE. Turt. Brit. Biv., p. 160, pi. viii, fig. 11, 1822. 

 Payr. Catal. Moll. Corse., p. 47, 1826. 

 Bronn. Leth. Geogn., ii, p. 954, t. xxxyiii, fig. 3a c, 1838. 

 Phil. En. Moll. Sic., vol. i, p. 40, vol. ii, p. 31. 

 Owen. Comp. Anat. Invert. An. p. 282, fig. 118, 1843. 

 Forbes. JSgean Invert. Rep. Brit. Assoc., p. 180, 1843. 

 Agass. Icon. des. Coq. Tert., p. 45, t. x, figs. 10 13, 1845. 



NITENS. Andr. Bull, de Sc. de Mosc. p. 104, pi. vi, fig. 9, 1830, fide Bronn. 



L^EVIS. Agass. Loc. cit. supra, t. x. 

 CYTHEREE FAUVE. Chenu. Traite Element., pi. iii, fig. 10. 



Encyc. Method., pi. 266, fig. 1 a. b, 



Spec. Char. Testa transversd, ovato-cordatd, incequilaterali, glabrd, politd, trans- 

 versim obsolete sulcatd ; lunuld elongatd ; antice et postice rotundatd. 



Shell transverse, ovate, heartshaped, inequilateral, very smooth, and glossy ; with 

 obsolete transverse ridges ; lunule elongate, and cordiform : anterior and posterior 

 sides rounded. 



Length, 2^ inches ; height, 1 f ditto. 



Locality. Cor. Crag, Ramsholt 



Recent, Britain, Mediterranean. 



This elegant and beautiful shell I have seen only from the oldest of the Crag 

 Deposits, and in that from the lowest part, where it is not rare, but of extreme 

 fragility, and specimens are very difficult to be obtained. 



The Crag shell agrees precisely with the British form of this species, in the exterior 

 being smooth and glossy, and marked in a concentric direction, with occasionally 

 shallow or indistinct furrows, or depressions, and with the aid of a lens may be seen 

 numerous, fine, radiating striae, most visible upon the posterior side ; these, however, 

 are quite superficial, and are not seen when the surface is removed, nor is it imparted 

 in any way to the margin of the shell which is quite smooth. 



27 



