ARCA. 33 
Affinities. —This species is distinguished by its prominent toothed carina and 
strong postero-dorsal ribs. Its forrm is somewhat similar to that of A. Sancte- 
Crucis, Pictet and Campiche (see p. 34), but its posterior margin is more oblique. 
It also appears to be related to Arca Dufrenoyi, d’Archiac,’ but in that form 
the antero-dorsal extremity is rectangular. The hinge of A. Dufrenoyi seems to 
be unknown. 
Types.—I have not seen the type; it came from the Neocomian of Marolles 
(Aube). 
Distribution.—Perna-bed of Atherfield; Atherfield Beds of East Shalford and 
Peasmarsh; Ferruginous Sands (upper beds) of Shanklin. 
Arca Carteront, d’Orbigny, 1844. Plate VI, figs. 4a—e, 5 a—e. 
1844. Arca Carreront, A. d’Orbigny. Pal. Frang. Terr. Crét., vol. iii, p. 202, 
pl. eecix, figs. 4—8. 
1845. — — E. Forbes. Quart. Journ. Geol. Soe., vol. i, p. 246. 
1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 185. 
1866. — — F. J. Pictet and G. Campiche. Foss. du Terr. Crét. de 
Ste. Croix (Matér. Pal. Suisse, ser. 4), pt. 38, pp. 436, 
468, pl. exxx, fig. 9. 
1853. — -- W. Keeping. Foss., &c., of Neoc. of Upware and Brick- 
hill, p. 114, pl. v, fig. 7. 
Description.—Shell oblong, very elongate and thick. Dorsal and ventral 
margins straight and nearly parallel. Hinge-line extends to the most anterior 
part of the shell, and forms with the anterior margin a right angle; the anterior 
margin curves ventrally from the hinge-line. Posterior margin a little oblique. 
Umbones of moderate size, widely separated, only slightly curved, with a low 
rounded carina extending to the postero-ventral angle; between the carina and 
the hinge-line is a second indistinct carina. Hinge-area very broad and large, 
lozenge-shaped, with several (about seven) ligament-grooves. Ornamentation 
consists of fine radial ribs. Hinge: the teeth near the umbo are small and 
transverse, but towards the extremities they become more oblique and longer. 
Measurements : (1) (2) 
Length . : . 40 ; . 28mm. 
Height . : é PG ; a8 Glows 
Thickness : : 20) ; i 
(1) From Upware. (2) From East Shalford. 
1 * Bull. Soe. Géol. de France,’ ser. 2, vol. xi (1854), p. 214, pl. iii, fig. 9. 
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