160 MOLLUSCA FROM THE CRAG. 



almost to have obliterated the radiating ridges. There appear to have been periods in 

 the life of the animal when the margin of the shell was more than ordinarily thickened, 

 as if the process of increase in the shell was delayed or interrupted, after which it 

 proceeded with more slender rays until they were again thickened, or rather strength- 

 ened. This fossil strongly resembles a northern form found in the sea of Ochotsck, 

 figured by Middendorff in his ' Russian Malacology,' t. xv, figs. 23 25, described 

 under the name of C. Calif orniense, Desh., but it is, I believe, specifically different, as in 

 that species (according to the figure) the posterior side is much less rounded than in 

 our Crag fossil ; the hinge also appears thicker, with a wider fulcrum for the ligament. 



10. CARDIUM VENUSTUM, 8. Wood. Tab. XIII, fig. 2 a b. 



Dale. Hist, and Antiq. of Harwich, p. 293, pi. xii, fig. 18, 1730. 



Spec. Char. Testa cordato-ovatd, odliqua, incsqmlaterali ; obsolete costatd, costis nume- 

 rosis depresses ; latere postico l&mgato. 



Shell ovately heartshaped, oblique, inequilateral ; obsoletely costated, ribs nume- 

 rous, depressed ; posterior side smooth, naked. 



Length, 2 inches; height, 2 inches. 



Localities. Red Crag, Walton-on-the-Naze, Sutton. 



This is one of the rarer shells of the Red Crag. Being unable satisfactorily to 

 assign it to any known species, I am reluctantly obliged to give it a new name. The 

 shell figured by Dale is evidently the same as ours, but I cannot, as he has done, refer 

 it to Lister's figure, which is C. Norvegicum; there is a strong general resemblance, but 

 the posterior side is too much rounded to be united with that species, and it was 

 probably a smoother shell than C. decorticatum of the Coralline Crag. 



11. CARDIUM GROENLANDICUM, Chemnitz. Tab. XIII, fig. 1 a d. 



CAKDIUM GB.OENLANDICUM. Chemn. Conch. Cab., t. vi, p. 202, t. xix, fig. 198, 1782. 



Gould. Invert. Massach., p. 92, 1841. 

 Holier. Ind. Moll. Groen., p. 20, 1842. 

 Dekay. Nat. Hist. New York Zool., p. 206, pi. xxiii, fig. 250. 

 Reeve. Conch. Icon. Card., pi. x, fig. 53. 

 Middendorff. Malacozoologia Rossica, (Me'm. de 1'Acad. Imp. 



des Sci. St. Petersb.,) p. 557, t. xvi, figs. 69, 1849. 

 EDENTULA. Mont. Test. Brit. Suppl., p. 29, 1808. 



EDENTULUM. G. Sow. Genera No. 34, Cardium, fig. 2. 



ANODONTA. Blainv. Man. Malac., p. 658, 1825. 



BOE.EALE. Reeve. Conch. Icon., pi. xxii, fig. 131. 

 MACTEA RADIATA. Don. Brit. Shells, vol. v, t. 161, 1803. 



APHKODITA COLUMBA. J. Lea. Trans. Amer. Phil. Soc., vol. v, p. 1 10, pi. xviii, fig. 54, 1833. 

 ACAKDO. Swains. Treat. Malac., p. 374, 1840. 

 SERRIPES. Seek. Fide Gould. 



MONODACNA PROPINQUA? Eichwald. Fauna Caspio-Caucasia, p. 275, t. xl, figs. 3, 4, 1841. 

 ? Encyc. Method., t. 300, fig. 7. 



