FROM TANGANYIKA AND KENYA 77 



Trigonia migeodi sp. nov. 

 PI. 11, figs. 11a, b 



Specific name. After the late F. W. H. Migeod, for some years leader of the 

 British Museum East Africa Expedition. 



Diagnosis. Small (length of holotype 17-5 mm.), moderately inflated, length 

 well in excess of height, umbones moderately prominent, marginal carina well 

 curved ; posterior area broad ; ventral margin rather feebly convex, almost straight 

 towards its posterior end. Flank ornamented with relatively narrow and numerous, 

 round-topped concentric ribs separated by intervals of almost the same width ; 

 number on each valve of holotype estimated at about 30 (those on umbonal region 

 worn away). Ribs almost reach carina on right valve. The posterior area has a 

 median groove and bears about 6 radial threads on its antero-ventral side and 

 probably about the same on its postero-dorsal side, where, however, they are not 

 well seen. 



Holotype. No. L.51193, a right valve. The only specimen. 



Locality and horizon, i mile N.W. of Tendaguru hill, Tanganyika ; Upper 

 Kimmeridgian, Nerinella Bed. 



Remarks. This specimen differs from T. kidugalloensis in its more elongate out- 

 line, its more strongly curved marginal carina, and its more closely spaced ribs. It 

 is quite close to the European Bajocian species T. hemisphaerica Lycett but has more 

 closely spaced ribs. It also much resembles T. tenuis Kitchin (1903 : 35, pi. 3, 

 figs. 5, 6), from the Upper Jurassic of India (re-named T. oomia by Strand 1928 : 72), 

 but it has more closely spaced ribs and a more conspicuous median groove on its 

 posterior area. 



Trigonia dainellii Venzo 

 PL 11, fig. 9 



1945. Trigonia (Lyriodon) dainellii Venzo : 15, figs. la-c. 



1949. Trigonia [Lyriodon) dainellii Venzo ; Venzo : 138, pi. 2, figs. 1-5. 



1949. Trigonia [Lyriodon) brevicostata Kitchin ; Venzo : 137, pi. 1, figs. 34, 35. 



i960. Trigonia sp. nov. [brevicostata Venzo non Kitchin) ; Joubert, pi. 7, figs. \a, b. 



Material. Several specimens. 



Localities and horizon. Odda, and W. slope of hill \ mile E. of Hafura, both 

 N.E. Kenya ; Uppermost Jurassic or basal Cretaceous, Danissa Beds. 



Remarks. The general form and the flank ornament of this species are those of a 

 typical costate Trigonia, but there is a tendency for the ribs to undulate irregularly 

 in later stages of growth. A peculiar feature of the specimens now recorded is that 

 the ribs of the flank are continued across the marginal carina, some of them bifurcat- 

 ing at the same time. There is a shallow, linear ante-carinal groove. The posterior 

 area bears two or three strong radial ribs, and in later stages of growth these are 

 crossed by transverse ridges. 



