ARCA. 33 



Affinities. —This species is distinguished by its prominent toothed carina and 

 strong postei-o-dorsal ribs. Its form is somewhat similar to that of A. Sanctse- 

 Crucis, Pictet and Campiche (see p. 34), but its posterior margin is more oblique. 



It also appears to be related to Area Dufrenoyi, d'Archiac, 1 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. — Pema-bed of Atherfield ; Atherfield Beds of Bast Shalford and 

 Peasmarsh ; Ferruginous Sands (upper beds) of Shanklin. 



Arca Cartekoni, (VOrbigny, 1844. Plate VI, figs. 4 a — c, 5 a — c. 



1844. Arca Carteroni, A. (VOrbigny. Pal. Franc. Terr. Cret., vol. iii, p. 202, 



pi. cccix, figs. 4 — 8. 



1845. — — E. Forbes. Quart. Journ. Geol. Soc, vol. i, p. 246. 

 1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 185. 



18(36. — — F. J. Pictet and O. Campiche. Toss, du Terr. Cret. de 



Ste. Croix (Mater. Pal. Suisse, ser. 4), pt. 3, pp. 436, 

 468, pi. exxx, fig. 9. 



1883. — — W. Keeping. Foss., &c, of Neoc. of Upware and Brick- 



hill, p. 114, pi. 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 



28 mm. 



Height . 





. 16 



13 „ 



Thickness 





. 20 



— „ 



(1) From 



Upware. 



(2) From East Shi 



ilford. 



' Bull. Soc. Geol. de France,' ser. 2, vol. xi (1S54), p. 214, pi. iii, fig. 9. 



