FROM TANGANYIKA AND KENYA 41 



and scarcely curved ridge runs from the beak to the ventral margin and separates the 

 flank from a narrow antero-ventral region, the margin of which presents only a slight 

 concavity below the beak and does not project anteriorly to it. Surface unornamen- 

 ted. 



Holotype and paratypes. Holotype, no. L.52187 ; numerous paratypes. 



Localities and horizons. Dirahara, 24 miles E.N.E. of Aus Mandula, N.E. 

 Kenya, and Tifo, 14 miles N. of Wergudud, N.E. Kenya ; Oxfordian, Golberobe 

 Beds. Tendaguru neighbourhood (Kindope valley, Tingutitinguti creek, Lilomba 

 creek), and Kinjele, 5 miles W. of Mtapaia, N. of Tendaguru, Tanganyika ; all 

 Upper Kimmeridgian, " Trigonia smeei " Bed. 



Remarks. Mytilus galliennei d'Orbigny, the Cenomanian species from France 

 to which this form was originally compared by Hennig, has a less marked diagonal 

 ridge, lacks any convexity of the anterior margin below the beak, and has weak 

 transverse striations on its antero-ventral region. 



Genus BRACHIDONTES Swainson 1840 



Subgenus ARCOMYTILUS Agassiz 1842 



Brachidontes (Arcomytilus) asper (J. Sowerby) 

 PI. 4, figs. 2a, b 



1818a. Modiola aspera J. Sowerby : 22, pi. 212, fig. 4. 



1948. Brachidontes (Acromytilus) asper (J. Sowerby) ; Cox & Arkell : 5. 



i960. Brachidontes (Arcomytilus) asper (J. Sowerby) ; Joubert, pi. 6, figs, ioa-c. 



Material. Two specimens (nos. L. 92067, L. 92177). 



Localities and horizons. 2 miles W. of Melka Biini, N.E. Kenya ; Bathonian, 

 Murri Limestones. Kulong, 2 miles S.W. of Muddo Erri, N.E. Kenya ; Callovian 

 [?-Lower Oxfordian], Muddo Erri Limestones. 



Remarks. The specimens now recorded are typical examples of this species, 

 which in England appears to be restricted to the Bathonian, but is known from the 

 Callovian of various other areas. 



Brachidontes (Arcomytilus) laitmairensis (de Loriol) 



PI. 4. %• 3 



1883. Mytilus laitmairensis de Loriol : 57, pi. 8, figs. 6-12. 



1935a. Mytilus (Arcomytilus) laitmairensis de Loriol ; Cox : 164, pi. 15, figs. 13, 14. 



i960. Mytilus (Arcomytilus) sp. ; Joubert, pi. 6, fig. 9. 



Material. Four specimens. 



Localities and horizons. Kulong, 2 miles S.W. of Muddo Erri, N.E. Kenya ; 

 Callovian [?-Lower Oxfordian], Muddo Erri Limestones. Tifo, 14 miles N. of 

 Wergudud, N.E. Kenya ; Oxfordian, Golberobe Beds. N. of Matapwa, Pindiro 

 area, Tanganyika ; Upper Kimmeridgian. 



