BARB ATI A. 37 



represent the same form, but that Leymerie's specimen was imperfect in the 

 postero-dorsal region. B. aptiensis appears to differ from B. Baulini 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 veri- 

 similar to A. neocomiensis , d'Orbigny. Judging from the figure the latter seems 

 to differ chiefly in having the posterior extremity pointed instead of obliquely 

 truncate. 



Area 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-Rhone 

 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 — Scaphula, Benson, 1834. 



[' Proc. Zool. Soc.,' pt. ii, p. 91.] 



Baebatia (Scaphula?) Austeni (Forbes), 1845. Plate VII, figs. 1 a, b, 2, 3. 



1845. Caedium (Hemicaedium) ? Austeni, F. Forbes. Quart. Journ. Geol. 



Soc, vol. i, p. 244, pi. iii, fig. 3. 

 1850. Aeca Austeni, A. d'Orbigny. Prodr. de Pal., vol. ii, p. 118. 

 1854. Caedium Austeni, J. Morris. Cat. Brit. Poss., ed. 2, p. 192. 

 1866. Aeca Austeni, F. J. Pictet and O. CampicJie. Poss. du Terr. Cret. de 

 Ste. Croix (Mater. 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 growtli ; 

 the radial ribs are sometimes indistinct, but on the postero-dorsal area they are 

 more prominent than elsewhere. Interior not seen. 



