no JURASSIC BIVALVIA AND GASTROPODA 



shallow, its bordering ridges rather obscure ; diagonal ridge distinct near umbo but 

 dying out before reaching postero- ventral corner of shell. Ornament consisting of 

 narrow and rather irregularly spaced concentric folds (obliterated by erosion on 

 part of surface of holotype). Internal characters unknown. 



Holotype. No. LL.35I43, ex B.P. Coll. There is also a fragment of a second 

 specimen. 



Locality and horizon. i\ miles N.N.W. of Kidugallo, Central Railway, 

 Tanganyika ; Bajocian. 



Remarks. This species is referred to Pronoella on account of its general resemb- 

 lance to P. pindiroensis sp. nov., from which it differs in its less elongate but more 

 strongly inequilateral form, its broader lunule, and its more strongly ribbed surface. 



Genus ANISOCARDIA Munier-Chalmas 1863 



Anisocardia arkelli sp. nov. 

 PI. 18, figs. 5«, b 



Specific name. After the late Dr. W. J. Arkell. 



Diagnosis. Of medium size (length of largest specimen 17-5 mm.), subtrigonal, 

 inequilateral, length well exceeding height, beaks at about anterior third of length ; 

 inflation strong. Umbo prominent, narrowly rounded, well incurved, with beak 

 strongly prosogyrous. Postero-dorsal outline feebly convex, steeply sloping ; 

 posterior margin low, sharply convex ; ventral margin of moderate and even con- 

 vexity ; anterior margin narrowly rounded, with anterior extremity low, at about 

 one-quarter of shell height ; antero-dorsal outline strongly concave. No distinct 

 posterior umbonal ridge present. 



Holotype and paratypes. Holotype, no. LL.35051. Four paratypes, nos. LL. 



35052-55- 



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. gibbosa (Minister) (Cox, 

 1947 : 161, text-figs. 29a, b), from the European Bajocian, but is smaller and less 

 gibbose. 



Anisocardia didimtuensis sp. nov. 

 PI. 18, fig. 4 



Diagnosis. Of medium size (length of holotype 20-8 mm.), subtrigonal, inequi- 

 lateral, length well exceeding height, beaks at about anterior third of length ; in- 

 flation strong ; umbo prominent, narrowly rounded, very strongly incurved, with 

 beak strongly prosogyrous. Postero-dorsal outline strongly convex near umbo, 

 slightly concave more posteriorly, steeply sloping, forming an obtuse angle with short, 



