134 JURASSIC BIVALVIA AND GASTROPODA 



1929. PCeratomya cf. wimmisensis (Gillieron) ; Weir : 31, pi. 3, fig. 1. 

 1935a. Ceratomya wimmisensis (Gillieron) ; Cox : 186, pi. 20, figs. 6a, b. 

 IQ 39- Ceratomya wimmisensis (Gillieron) ; Stefanini : 248, pi. 25, figs. 5, 6. 



Material. One specimen (no. L.83881). 



Locality and horizon. 14 miles W.S.W. of Rahmu, N.E. Kenya. Callovian 

 [?-Lo\ver Oxfordian], Muddo Erri Limestones. 



Remarks. This specimen shows the abrupt discordancies in ribbing characteristic 

 of this species, patches of oblique ribs occupying parts of the surface and concentric 

 ribs the remainder. The arrangement of the ribbing is altogether dissimilar on the 

 two valves. The specimen is not well enough preserved for illustration. 



Ceratomya wilder riensis sp. no v. 



PI. 21, fig. 5 



i960. Ceratomya excentrica (Roemer) ; Joubert, pi. 11, fig. 1 (non Roemer sp.). 



Diagnosis. Shell moderately large (length of holotype c. 87 mm.), ovate, with 

 height about three-quarters of length, strongly inequilateral, evenly and moderately 

 strongly inflated. Umbo terminal, strongly prosogyrous and incurved, its outline 

 continuous with postero-dorsal outline of shell, which rises slightly above it before 

 curving gently down to meet the evenly convex posterior margin. Ventral margin 

 moderately and evenly convex. Umbonal ridges absent. Ornament consisting of 

 closely and fairly evenly arranged, rounded concentric ribs (about 8 to the cm. on 

 middle of shell), separated by narrower intervals. 



Holotype and paratype. Nos. L. 92226 and L. 92246 respectively, two speci- 

 mens in all. 



Localities and horizon. Dusse, i\ miles S.E. of Rahmu, N. Kenya (type- 

 locality). Wilderri hill, 11 miles S.S.W. of Rahmu. Both Upper Oxfordian, Seir 

 Limestones. 



Remarks. This species, with its purely concentric ornament, belongs to the group 

 of Ceratomya concentrica (J. de C. Sowerby), differing from that species in the termin- 

 al position of its umbo, in the even convexity of its surface (the postero-dorsal region 

 is not in the least pinched-in), and in its larger size. In C. paucilirata (Blanford) 

 (1870 : 203, pi. 8, fig. 6 ; also Futterer 1897 : 610, pi. 22, fig. 1), Upper Jurassic of 

 S. Abyssinia, the umbo is more prominent and less anteriorly placed, the postero- 

 dorsal region is not so evenly convex, and the concentric ribs are broader. In C. 

 egerkingensis (Gerber) (1918 : 6, pi. 1, fig. 1), Lower Kimmeridgian of Switzerland, 

 the umbo is much more prominent and less anteriorly placed. 



