24 JURASSIC BIVALVIA AND GASTROPODA 



and Myopholas manderaensis sp. nov. Some hundreds of feet higher (according to 

 Joubert's reading of the succession), and separated from this bed by almost unf ossi- 

 ferous deposits, are the Finaguba Beds, which are of interest to palaeontologists as 

 yielding the assemblage monographed and regarded as of Bathonian age by Venzo 

 (1949). No specimens from the locality Cud Finagubi itself (the source of most of 

 Venzo's material) have been examined, but a short discussion on the age of this 

 assemblage, based on his illustrations, may be appropriate at this point. 



The most abundant fossils are trigoniids, belonging to what I would regard as only 

 two species, Trigonia dainellii Venzo (this includes specimens identified by Venzo 

 as the Callovian species T. brevicostata Kitchin) and T. stefaninii Venzo. T. dainellii 

 belongs to a subgenus of Trigonia which has not yet received a name but is represented 

 in the Upper Jurassic of Europe by a species identified by de Loriol (1868 : 160, pi. 

 10, figs. 12-16 ; 1872 : 295, pi. 16, fig. 20) as Trigonia truncata Agassiz. In the 

 Yonne Department of France this species occurs (de Loriol 1868 : 252) only a few 

 feet below the Cretaceous in beds which appear to be referable to the Portlandian 

 (as restricted by British geologists), but in the Haute-Marne it occurs (de Loriol 

 1872 : 498, 499) in beds which would be included in the Kimmeridgian in the British 

 sense, while in northern Germany Credner (1863 : 22, 36) records it from well down 

 in the Kimmeridgian. The similarity between T. dainellii and T. truncata, possibly 

 amounting to the specific identity of the two forms, thus strongly suggests that the 

 Finaguba Beds are Upper Jurassic (Kimmeridgian or Portlandian) in age. The 

 second trigoniid, Trigonia [now Rutitrigonia] stefaninii Venzo, has already been 

 commented upon when discussing the fauna of the Dakacha Limestones. Although 

 belonging to a genus previously reported only from the Cretaceous, the presence of 

 this species in N.E. Kenya in beds of which the Upper Jurassic age could not be 

 disputed shows that it does not provide evidence for a Cretaceous age for the 

 Finaguba Beds. Apart from the trigoniids and some small nondescript oysters, 

 these beds yielded a large number of internal moulds of bivalve shells not all identifi- 

 able with any certainty even generically. Venzo's application to these of the names 

 of such Bathonian species as Eonavicula eudesii (Morris & Lycett), Anisocardia 

 loweana (Morris & Lycett), Sphaera madagascariensis (Newton) and Quenstedtia 

 morrisi (Cossmann) has no stratigraphical significance. The same remark applies 

 to the identification of Grammatodon (Indogrammatodon) virgatus (J. de C. Sowerby) 

 in this fauna. This subgenus Indogrammatodon is undoubtedly represented by more 

 than one species, but it is not obvious what specific names should be applied to such 

 poor material. My present view, taking into consideration the stratigraphical 

 evidence adduced by Joubert, is that the Finaguba Beds are of Upper Kimmeridgian 

 if not of still later Jurassic age. 



The beds of the Mandera Series are succeeded by deposits for which the term 

 Marehan Series has been adopted (Saggerson & Miller 1957 : 23 ; Joubert i960 : 39). 

 The lower of the two divisions of this series (the Danissa Beds) has been dated as 

 Lower Cretaceous on palaeobotanical evidence which is not altogether convincing. 

 A fossiliferous horizon in these beds has yielded a form (Trigonia dainellii Venzo) 



