208 MOLLUSCA FROM THE CRAG. 



Poll has given a beautiful drawing of the animal of this species, and its anatomy is 

 described by Professor Owen in his Lectures upon Invertebrate Animals, where he 

 considers it as one of the most highly organised of the Bivalvia. In the recent 

 state this does not appear to have been a very deep water species, and seems more 

 inclined to the southern or Mediterranean regions, where it is very abundant, and as 

 a fossil I know it only from the Sicilian beds, unless Venus chionoides, Nyst, be one of 

 its varieties. C. Chione, Dubois, Wolhyn. Podol., pi. v, figs. 13, 14, appears to 

 have ridges too regular and too numerous, and according to the figure, is rather too 

 broad on the posterior side, with the sinus in the mantle mark more rounded, and 

 appears to be intermediate between our shell and Erycinoides. 



Cytherea nitidula, Lam., a recent species from the Mediterranean, is considered by 

 Philippi as the young of this shell, but the fossil from the older Tertiaries described 

 under the same name, is quite distinct. 



2. CYTHEREA RUDIS, Poll. Tab. XX, fig. 5 a d. 



VENUS RUDIS. Poli, (not Dujard.) Test. Sicil., vol. ii, p. 94, t. xx, figs. 15, 16, 1795. 

 Middendorff. Malacozool. Rossica, p. 571, 1849. 



PECTUNCULUS. Broc. Conch. Foss. Subap., p. 560, pi. xiii, fig. 12, 1814. 



CYCLADIFORMIS. Nyst. Coq. Foss. de Belg., p. 171, pi. xii, fig. 3, 1844. 



VENETIANA. Sismonda. Syn. Meth. Invert. Pedm., p. 20, 1847. 



OCHROPICTA. Krynicki. Bull, des Natur. de Mosc., No. 11, p. 64, fide Middendorff. 

 CYTHEREA VENETIANA. Lam. Hist, des An. s. Vert., torn, v, p. 569, 1818. 



Phil. En. Moll. Sic., vol. i, p. xl, t. iv, fig. 8, 1836. 



Dujard. Mem. de la Soc. Geol. de Fr., t. ii, part ii, p. 260, 1837. 



Forbes. ^Igean Invert. Rep. Brit. Assoc., p. 182, 1843. 

 FILOSA. S. Wood. Catalogue, 1840. 

 CYCLADIFORMIS. Nyst. Rech. Coq. Foss. d'Anv., p. 10, No. 38, pi. ii, fig. 38, 



1835. 

 RUDIS. Phil. En. Moll. Sic., vol. ii, p. 32, 1844. 



Spec. Char. Testa oblique-cordatd, tumidd, inaquilateraU, tenui, transversim striatd, 

 striis tenuibus, rotundatis, confertis ; lunuld elongato-cordatd, margine integro ; umbonibus, 

 prominulis. 



Shell obliquely heartshaped, tumid, inequilateral, thin, transversely or concen- 

 trically striated ; striae fine, close, and rounded ; lunule of an elongated heartshape ; 

 margin smooth ; beaks slightly prominent. 



Length, ^ths of an inch ; height., fths of an inch. 



Localities. Cor. Crag, Button, Ramsholt, Sudbourn. 



Red Crag, Button, and Walton-on-the-Naze. 



Recent, Mediterranean, and Black Sea. 



This delicate and elegant shell is very abundant in the Red Crag at Walton-on- 

 the-Naze, and not at all rare in the Lower Formation, or Cor. Crag at Sutton. 



It is subject to considerable variation in outline, and in proportional dimensions, 



