32 CRETACEOUS LAMELLIBRANCHIA. 
Family—ARCIDA, Lamarck. 
Genus—Anca, Linneus, 1758 (sensu stricto). 
(‘ Syst. Nat.,’ ed. 10, p. 693.) 
1. Lower Cretaceous Species. 
Arca Dupryrana, d’Orbigny, 1844. Plate VI, figs. 1a, b, 2, 3. 
1844. Arca Dupintana, dA. d’Orbigny. Pal. Franc. Terr. Crét., vol. iii, p. 207, 
pl. ecex, figs. 9, 10. 
1845. — _ E. Forbes. Quart. Journ. Geol. Soc., vol. i, p. 246. 
1850. — — A.d’Orbigny. Prodr. de Pal., vol. ii, p. 80. 
1854 -- — J. Morris. Cat. Brit. Foss., ed. 2, p. 185. 
1855 — — G. Cotteau. Moll. Foss. de l’Yonne, p. 86. 
1866 _— — F. J. Pictet and G. Campiche. Foss. du Terr. Crét, 
Ste. Croix (Matér. Pal. Suisse, ser. 4), pt. 3, 
pp. 438, 468. 
1867. — — P. de Loriol. In A. Favre, Recherch. géol. dans 
Savoie, &e., vol. i, p. 381. 
1871. — — F. Stoliczka. Paleont. Indica, Cret. Fauna 8. India, 
vol. iii, p. 842 (Barbatia). 
Description.—Shell elongate, very inequilateral, convex. Anterior margin 
rounded. Ventral margin sinuous, roughly parallel to the hinge-line. Posterior 
margin very oblique, nearly straight, forming sharply marked obtuse and acute 
angles with the dorsal and ventral margins respectively. Umbones prominent, 
moderately distant, with a prominent toothed carina extending to the postero- 
ventral angle, and cutting off a depressed postero-dorsal area. Hinge-line long. 
Hinge-area rather large. Ornamentation consists of numerous fine radial ribs— 
more prominent at the anterior end—crossed by concentric growth-lines. Pos- 
tero-dorsal area with four strong radial ribs which project posteriorly, giving a 
toothed margin. Teeth numerous, small, transverse, the terminal teeth slightly 
oblique. 
Measurements : 
Leneth . p : ; , , : ‘ » 25) mm, 
SH Dar 
Height . : , ; : . : : . diosa. 
Thickness , . : ; ; . ‘ > I 
