208 MOLLUSCA FROM THE CRAG. 
Poli 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., pl. 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 Lrycinoides. 
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, Poli. Tab. XX, fig. 5 a—d. 
Vents rupIs. Poli, (not Dujard.) Test. Sicil., vol. ii, p. 94, t. xx, figs. 15, 16, 1795. 
= = Middendorff. Malacozool. Rossica, p. 571, 1849. 
— prctuncuLus. Broce. Conch. Foss. Subap., p. 560, pl. xiii, fig. 12, 1814. 
— cycLapirormis. Nyst. Coq. Foss. de Belg., p. 171, pl. xii, fig. 3, 1844. 
— Venetrana. Sismonda. Syn. Meth. Invert. Pedm., p. 20, 1847. 
— ocnropicta. Krynicki. Bull. des Natur. de Mosc., No. 11, p. 64, fide Middendorf. 
CytHEreA VENETIANA. Lam. Hist. des An. s. Vert., tom. v, p. 569, 1818. 
— — Phil. En. Moll. Sic., vol. i, p. xl, t. iv, fig. 8, 1836. 
_— _ Dujard. Mem. de la Soe. Geol. de Fr., t. ii, part ii, p. 260, 1837. 
— — Forbes. Aigean Invert. Rep. Brit. Assoc., p. 182, 1843. 
— ritosa. SS. Wood. Catalogue, 1840. 
— cycLapirormis. Nyst. Rech. Coq. Foss. d’Anv., p. 10, No. 38, pl. ii, fig. 38, 
1835. 
— ruvIs. Phil. En. Moll. Sic., vol. i, p. 32, 1844. 
Spec. Char. Testé oblique-cordatd, tumidd, inequilaterah, tenui, transversim striata, 
striis tenuibus, rotundatis, confertis ; lunula elongato-cordatd, margine integro ; umbonibus, 
prominulis. 
Shell obliquely heartshaped, tumid, inequilateral, thin, transversely or concen- 
trically striated ; striz fine, close, and rounded; lunule of an elongated heartshape : 
margin smooth ; beaks slightly prominent. 
Length, Zths of an inch ; height, $ths of an inch. 
Localities. Cor. Crag, Sutton, Ramsholt, Sudbourn. 
Red Crag, Sutton, 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, 
e* 
