io JURASSIC BIVALVIA AND GASTROPODA 



Limestone, now definitely established by ammonites to include both Upper Bajocian 

 and Bathonian horizons, was the source of most of the material in this collection, but 

 there were also specimens from higher horizons of the Jurassic. Weir's paper 

 included descriptions of the following new species : Nucula woodae [Kambe Lime- 

 stone], Nucula (Pa/aeonitcula) gregoryi [Miritini Shales (Callovian)], Lopha krumbecki 

 [Oxfordian-Kimmeridgian], Chlamys (Acqiiipecten) spathi [Kambe Limestone], 

 Plesiopecten kenyana [Kambe Limestone], Lima (Pseudolimea?.) woodae [Kambe 

 Limestone]. 



A series of bivalves and gastropods collected mainly from the locality Cud- 

 Finagubi, about 3 miles S. of Mandera, in N.E. Kenya near the frontier with Somalia, 

 formed the subject of a series of notes by Venzo (1942a, b, 1943, \^\a-c, 1945), 

 followed by a larger memoir (Venzo 1949). About half the bivalves were identified 

 (some with qualification) with previously described species and it was concluded 

 that the age of the assemblage was Bathonian. Twenty species, a few with nume- 

 rous named varieties, were described as new. Later field work has led to the con- 

 clusion that the beds yielding this assemblage belong to a horizon very high in the 

 Jurassic and that some of Venzo's specific identifications are to be queried. The 

 age of the Cud Finagubi assemblage is discussed later in the present memoir (p. 24). 



Several reports of the Kenya Geological Survey published from 1952 onwards 

 have included lists of Jurassic bivalves and gastropods, mainly from N.E. Kenya, 

 based partly on identifications by the present writer, and in two of these (Saggerson 

 & Miller 1957 ; Joubert i960) some of the specimens have been illustrated photo- 

 graphically. Of publications of the Tanganyika Geological Survey, particular 

 reference must be made to the Bulletin by Aitken (1961) dealing with the Mandawa- 

 Mahokondo area of southern Tanganyika. This work includes a statistical study 

 of African specimens of the trigoniid subgenus Indotrigonia, which comprises Tri- 

 gonia smeei J. de C. Sowerby and related species. Aitken concludes that the true 

 T. smeei, which, as already mentioned, occurs typically in India in beds of Oxfordian 

 age, has not yet been found in East Africa, and that the common species of the 

 Upper Kimmeridgian beds at Tendaguru is a distinct form to which he assigns the 

 name Trigonia {Indotrigonia) africana. The following other trigoniids are also 

 described in the same paper: Trigonia (Indotrigonia) mandawae sp. nov. [Lower to 

 Upper Kimmeridgian], T. (I.) beyschlagi Muller [" Tithonian "], T. (I.) robusta sp. 

 nov. [" Tithonian "], T. (I.) v-striata sp. nov. [" Tithonian "], T. (Trigonia) tangany- 

 icensis sp. nov. [Middle or Upper Kimmeridgian], Laevitrigonia curta sp. nov. 

 ' Tithonian "], Opisthotrigonia curvata sp. nov. [" Tithonian "]. In addition, many 

 bivalve species belonging to other families are listed from various horizons. 



Ill EAST AFRICAN JURASSIC BIVALVE AND GASTROPOD FAUNAS 

 AND THEIR CHARACTERISTICS 



Liassic Assemblage 



The oldest beds anywhere in Kenya or Tanganyika assignable on fossil evidence to 

 the Jurassic system are limestones exposed at Didimtu Hill, 2 miles N.E. of Bur 

 Mayo, in N.E. Kenya. These beds are separated from the ancient rocks of the 



