The Cretaceous Fauna of Pondoland. 305 



Gosau, but has a longer lunular margin, a longer lunular tooth in 

 the left valve, and the posterior margin is less truncated. 



Mebetrix euglypha, sp. nov. 

 Plate XXXVI., figs. 7-10. 



Description.— ^YieW oval, of moderate or small convexity. Margin 

 near the lunule concave. Anterior margin well rounded, and forming 

 a continuous curve with the ventral margin. Posterior margin 

 rounded, but often slightly truncate. Postero-dorsal margin with 

 a gentle curvature. Umbones of moderate size, curving slightly. 

 Lunule small, elongate, bounded by a groove. 



Ornamentation consists of numerous strong, sharp, regularly con- 

 centric ribs, separated by deep and narrow grooves. The ribs are 

 usually continued on to the lunule. 



Interior of valves not seen. 



Length 21 . 25 . 23 . 22 . 21 . 19 mm. 

 Height 25 . 20 . 19 . 18 . 17 . 15 „ 



Affinities. — M. Hornesi (Zittel) * from the Gosau Beds, is similar 

 to this species in outline and ornamentation, but the umbones have 

 a greater curvature anteriorly, the valves are less flattened, and the 

 lunule is smooth. 



M. fahulina (Stoliczka) f differs from M. eughjplia in the more 

 anterior position of its umbones ; in having fewer ribs, which cut the 

 postero-dorsal margin less obUquely, and in the broader lunule and 

 distinct escutcheon. M. discoidalis, Stoliczka,]: is less elongate. 



M. arata, Gabb, § has larger and more prominent umbones and 

 its ornamentation consists of " impressed lines." 



M. Horni, Gabb, || is similar to M. euglypha, but the posterior end 

 is narrower, so that the outline of the valve is more ti'igonal. 



M. (?) kaffraria (Etheridge) * may, perhaps, be closely allied 

 to M. euglypha, but the figures do not give a clear idea of the 

 characters of the species. 



This appears to be the species which was referred by Griesbach to 

 Venus arcotensis, Forbes. 



* Bivalv. d. Gos.augeb., i. (1865), p. 126, pi. iii., fig. 5. 

 t Ci-et. Fauna S. India, vol. iii. (1870), p. 174, pi. xvi., figs. 31-33. 

 + Ibid., p. 17o, pi. vii., figs. 30, 31. 



§ Geol. Surv. California, Palseont., vol. i. (1864), p. 166, pi. xxx., fig. 2.50. 

 II Ihid., p. 164, pi. xxiii., fig. 144. 



H Second Report Geol. Survey Natal and Zululand (1904), p. 81, pi. ii., 

 figs. 20-22. 



