4 o JURASSIC BIVALVIA AND GASTROPODA 



forming an angle of about 45 ° with the hinge-margin), variable in breadth, moderate- 

 ly inflated ; dorsal margin not much elongated, meeting the convex posterior margin 

 in a broad curve. A very sharp ridge, strongly curved and forming almost a quad- 

 rant, runs from the beak to the ventral extremity and separates the flank from a 

 narrow antero-ventral region which slopes steeply to the margin and protrudes 

 beyond the ridge, so as to be visible in the side-view of the shell only near the beak. 

 Surface ornament unknown, the specimens being internal moulds. 



Holotype and paratypes. Holotype, no L.93615. Three paratypes, nos. 

 L.93581, L.93616-17. 



Localities and horizon. Tifo, 14 miles N. of Wergudud, and Ogar Wein hills, 

 17 miles N.W. of Wergudud, N.E. Kenya ; Oxfordian, Golberobe Beds. 



Remarks. The specimens upon which this species is founded were originally 

 recorded (Saggerson & Miller 1957 : 14) as Lycettia dalpiazi Venzo. On careful 

 examination, however, they prove to belong to a species of Falcimytilus in which the 

 diagonal ridge is unusually sharp, as they differ from Lycettia in the distinct protru- 

 sion of the anterior margin beyond the ridge. Mytilus (Falcimytilus) suprajurensis 

 Cox (1925 : 142, pi. 1, fig. 9 ; pi. 3, fig. 2 ; 1937c : 344, pi. 17, figs. 1-3), from the 

 Kimmeridgian and Portlandian of England, is a closely related but rather larger 

 species. 



Mytilus (Falcimytilus) jurensis Roemer 



1836. Mytilus jurensis [ex Merian MS.] Roemer : 89, pi. 4, fig. 10. 

 1935a. Mytilus jurensis Roemer ; Cox : 161, pi. 15, figs. 15-17. 



Material. Six specimens. 



Localities and horizons. Romicho, 25 miles S.W. of El Wak, N.E. Kenya ; 

 beds just underlying Golberobe Beds (Oxfordian). i\ miles S.W. of Rahmu, N.E. 

 Kenya ; Oxfordian, Rahmu Shales. Dusse, 1^ miles S.E. of Rahmu, N.E. Kenya ; 

 Upper Oxfordian, Seir Limestones. Hereri river crossing, 3 miles S. of Melka 

 Kunha, N.E. Kenya ; Kimmeridgian, Hereri Shales. 



Remarks. Like those from Somaliland figured in the work cited (Cox 1935a), 

 these specimens vary considerably in obliquity and in the development of an antero- 

 ventral bulge, which gives some of them a modioliform outline. 



Mytilus (Falcimytilus) dietrichi sp. nov. 

 PL 3, figs. 15, 16 



19146. Mytilus cf. galliennei d'Orbigny ; Hennig : 157, pi. 14, figs. 3a, b. 

 1933. Mytilus sp. ; Dietrich : 72. 



Diagnosis. Of medium size (diagonal measurement from beak to postero-ventral 

 corner 33 mm. in holotype), oblique (the diagonal forming an angle of about 45 ° 

 with the hinge-margin), variable in breadth, moderately inflated ; dorsal margin not 

 much elongated, meeting the convex posterior margin in a broad curve. A blunt 



