288 Annals of the South African Museum. 



Ornamentation consists of numerous narrow, slightly raised ribs 

 separated by linear grooves. On the postero-dorsal region the ribs 

 become larger and more prominent. Concentric growth-lines, or 

 lamellae, occur and become more distinct on the postero-dorsal 

 region. 



Length 21 mm. ; height, 14 mm. 



Affinities. — This species, of which I have seen a single left valve 

 only, appears to be distinct from other Cretaceous forms of Barhatia. 

 It presents a slight resemblance to the Aachen species figured by 

 Holzapfel ''•'■ as Area, cf. Gallienei, d'Orbigny, but is less convex, and 

 has the posterior margin more oblique, and the ornamentation on 

 the posterior area more strongly developed. 



Barbatia, sp. 



A single imperfect left valve resembles the last species, but is 

 much larger and has a much more distinct ridge passing from the 

 umbo to the postero-ventral extremity. 



Length about 100 mm. ; height 50 mm. 



Genus TKIGONOARCA, Conrad. 



Tkigonoarca capensis (Griesbach). 



Plate XXXIV., figs. 1, 2. 



1871. Area eapensis, Griesbach, Q.J.G.S. xxvii., p. 66, pi. iii., 



fig. 10. 



Dcseription. — Shell stout, quadrate or sub-trapezoidal, moderately 

 convex ; length a little greater than height, but sometimes nearly 

 equal. Anterior margin slightly or moderately convex, forming an 

 angle with the dorsal margin and curving regularly at the antero- 

 ventral margin. Ventral margin slightly curved or almost straight, 

 placed a little obliquely. Posterior margin slightly convex, oblique, 

 forming an acute angle with the ventral margin and an obtuse angle 

 with the hinge-margin. Umbones of moderate size, incurved, nearly 

 median, but behind the middle of the hinge-area. Carina rounded; 

 the part of the valve behind it flattened but slightly convex and 

 sloping very rapidly to the posterior margin. Hinge-area long, 

 depressed, with its antero-dorsal margin raised, and with four liga- 

 ment grooves. 



Ornamentation inconspicuous, consisting of numerous slightly 

 raised radial ribs which are somewhat wavy and separated by narrow, 



' MoUusk. Aachen. Kreide (1889), p. 204, pi. xxii., fig. 7. 



