FROM TANGANYIKA AMD KENYA m 



subvertical posterior margin ; ventral margin of even and very feeble convexity ; 

 anterior margin abruptly rounded, anterior extremity low, at about one-fifth of shell 

 height. No well-defined posterior umbonal ridge present. 



Holotype. No. L. 35056. The only specimen. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. This species appears to be distinct from A. arkelli, with which it 

 occurs associated. The umbo is more elevated than in that species, the beak 

 considerably more incurved and strongly prosogyrous, and the antero-dorsal outline 

 more excavated. The slight concavity of the postero-dorsal outline, moreover, is 

 not seen in A. arkelli. 



A specimen from the Upper Lias of Madagascar figured by Thevenin (19086 : 29, 

 text-fig. 24) as Gresslya cf. pingnis Agassiz is not a Gresslya, but an Anisocardia which 

 differs from the species now described in its rather higher anterior extremity and its 

 less strongly prosogyrous beak. Anisocardia fullonica Cox (1947 : 164, text-figs. 

 34a, b ; pi. 9, fig. 73), from the Lower Bathonian (Fuller's Earth Rock) of southern 

 England, closely resembles the form now described but is more tumid and has a less 

 evenly convex ventral margin. 



Anisocardia ayersi sp. nov. 

 PI. 18, figs. 6a, b 



Specific name. After Mr. F. M. Ayers, of the Kenya Geological Survey, who 

 first discovered the beds at Didimtu. 



Diagnosis. Of medium size (length of holotype 20-5 mm.), subovate, length 

 slightly exceeding height, beaks at about anterior quarter of length, inflation moder- 

 ate. Umbo not prominent, narrowly rounded in outline, moderately incurved and 

 prosogyrous. Postero-dorsal outline feebly convex, sloping gently, and forming an 

 obtuse angle with the straight, slightly oblique posterior margin ; ventral margin of 

 moderate and even convexity ; antero-dorsal outline slightly concave ; anterior 

 margin broadly rounded, anterior extremity at about one-third of shell height. No 

 distinct posterior umbonal ridge present. 



Holotype. No. LL. 35057. The only specimen. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. This species bears some resemblance to A. stamfordensis Cox (1947 : 

 160, text-figs. 24a, b ; pi. 9, fig. 72), Bajocian of England, but its umbo is less promin- 

 ent, it lacks a posterior umbonal ridge, and its ventral margin is not flattened poste- 

 riorly, as in that species. 



