CUCULLtEA. 63 



Cucull.ea Mailleana {d'Orbigny), 1844. Plate XIII, figs. 4 a — c, 5 a, b. 



1832. CucuLLiEA glabha, A. Passy (non Sowerby). Geol. de la Seine-Infer., 



p. 8 (of exp]. of plates), pi. xiv, fig. 10. 

 1844. Aeca Mailleana, A. d'Orbigny. Pal. Franc. Terr. Cret., vol. iii, p. 229, 



pi. cccxviii, figs. 3 — 7. 

 1850. — — — Prodr. de Pal., vol. ii, p. 164. 



? 1852. — — B. Kner. Denkscbr. d. k. Akad. Wissensch. Math.-nat. 



Sc, vol. iii, p. 313, pi. xvii, fig. 25. 

 1866. — — F. J. Pictet and G. Campiche. Foss. Terr. Cret. de Ste. 



Croix (Matt'r. Pal. Suisse, ser. 4), pt. 3, p. 475. 

 1871. — — F. Stoliczka. Palteont. Indica, Cret. Fauna S. India, 



vol. iii, p. 343 (Triyonoarca). 



Description. — Shell oval or rhomboidal, convex, oblique, highest posteriorly. 

 Anterior margin gently curved, relatively short. Posterior margin rather long, 

 oblique, slightly curved. Ventral margin with a considerable slope posteriorly, 

 forming an acute, but rounded, angle with the posterior margin. Umbones 

 rather small, .with a carina extending to the postero-ventral angle. A curved 

 ridge passes from the umbo to just above the middle of the posterior side. Hinge- 

 area rather narrow. Ornamentation consists of well-marked concentric grooves, 

 with faint radial ribs on- the posterior and anterior portions of the shell. Lateral 

 teeth parallel to the hinge-line. 



Measurements : 



(i) (2) 



Length ... 26 . .25 mm. 



Height . . . 22-5 . ". 21 „ 



Thickness ,. ,. .. 18-5, .. ..18 „ 



Affinities. — This species can be distinguished from G. glabra, Sowerby, by the 

 great obliquity of the ventral margin of the shell, the shorter area, and the much 

 less distinct radial, and better-marked concentric, ornamentation. 



The larger forms of G. obesa are readily distinguished from C. Mailleana; in 

 the smaller the outline of the shell is more rounded, the posterior angle is less 

 sharp, the carina more rounded, and the concentric grooves less distinct than 

 in Mailleana. D'Orbigny compares this species with C. Cornuelia?ia, but in that 

 form the ventral margin is more nearly parallel to the hinge-line. 



In form, some examples of G. Mailleana resemble Area Dumortieri, d'Archiac, 1 

 but the character of the ornamentation appears to be different. 



1 ' Bull. Soc. Geol.de France,' ser. 2, vol. xi (1854), p. 213, pi. xi, figs. 8, 8 a— d. 



