BARBATIA. 37 
represent the same form, but that Leymerie’s specimen was imperfect in the 
postero-dorsal region. B. aptiensis appears to differ from B. Raulini in the greater 
height of the posterior part of the shell and consequent greater obliquity and 
curvature of the ventral margin, and in the presence of a few radial ribs, stronger 
than the others, on the anterior part of the shell. The average size of the English 
form appears to be greater than that of the French. B. aptiensis is also very 
similar to A. neocomiensis, VOrbigny. Judging from the figure the latter seems 
to differ chiefly in having the posterior extremity pointed instead of obliquely 
truncate. 
Arca cymodoce, Coquand, is perhaps identical with this form, but its area 
appears to be shorter. 
Types.—From the Crackers of Atherfield and the Aptian of the Perte-du-Rhéne 
and Presta. 
Distribution. —Perna-bed, Atherfield Clay, and Crackers of Atherfield; Ferru- 
ginous Sands of Sandown; Atherfield Beds of Haslemere, East Shalford, and 
Sevenoaks. 
Sub-genus—Scarnvra, Benson, 1834. 
[‘ Proc. Zool. Soe.,’ pt. ii, p. 91.] 
BarBatia (ScapHuta ?) Austeni (Forbes), 1845. Plate VII, figs. 1a, b, 2, 3. 
1845. Carprum (Hemrcarpium) ? Ausrent, E. Forbes. Quart. Journ. Geol. 
Soc., vol. i, p. 244, pl. iii, fig. 3. 
1850. Arca AusTENI, A. d’Orbigny. Prodr. de Pal., vol. ii, p. 118. 
1854, Carprum Avstent, J. Morris. Cat. Brit. Foss., ed. 2, p. 192. 
1866. Arca Avsrent, F. J. Pictet and G. Campiche. Foss. du Terr. Crét. de 
Ste. Croix (Matér. Pal. Suisse, ser. 4), pt. 3, p. 471. 
Description.—Shell oval, very oblique and inequilateral. Anterior margin 
rounded, passing gradually into the curved and oblique ventral margin. Posterior 
margin a little convex, oblique, forming an acute angle with the ventral margin. 
Umbones of moderate size, incurved, with a very sharp carina extending to the 
postero-ventral angle; postero-dorsal area sharply depressed. Hinge-line short. 
Hinge-area small, triangular, with several ligament-grooves. Ornamentation 
consists of slightly elevated radial ribs crossed by faintly marked lines of growth ; 
the radial ribs are sometimes indistinct, but on the postero-dorsal area they are 
more prominent than elsewhere. Interior not seen. 
