FROM TANGANYIKA AND KENYA 81 



Remarks. This is a very typical Laevitrigonia, differing from the type-species, 

 L. gibbosa (J. Sowerby), in the absence of an ante-carinal depression, but comparable 

 to some other species from the Upper Jurassic of Europe, for example, L. acteon 

 (Munier-Chalmas) (1882 : 503, pi. 12, fig. 5) and L. oustaleti (Munier-Chalmas) (1882 : 

 503, pi. 12, fig. 7). It differs from previously known species in details of ornament. 



Genus RUTITRIGONIA Van Hoepen 1929 



Rutitrigonia stefaninii (Venzo) 



PL 12, figs. 3a, b 



1942a. Trigonia (Laevitrigonia) stefaninii Venzo : 27, fig. 10. 



1949. Trigonia (Laevitrigonia) stefaninii Venzo ; Venzo : 145, pi. 2, figs. 28-33 ; also figs. 



34-50 (varieties). 

 i960. Trigonia stefaninii Venzo ; Joubert, pi. 7, figs. 2a, b. 



Material. Two specimens (nos. L. 92180, L. 92273). 



Localities and horizon. 3 miles N.E. of Melka Dakacha, N.E. Kenya, and 2 

 miles S. of Melka Dakacha ; Upper Kimmeridgian, Dakacha Limestones. 



Remarks. The better preserved specimen, now figured, is a trigonally ovate 

 shell in which the posterior carina fades away after an early stage of growth and the 

 weak, undulating ribs are confined to the anterior end of the flank. It is closely com- 

 parable to some of Venzo's figures. This is obviously a variable species and the 

 numerous varietal names introduced by Venzo seem unnecessary. 



This species is of some interest as it appears to belong to the genus Rutitrigonia, 

 hitherto known only from Cretaceous rocks. Its umbo is rather more prominent 

 than in the more typical representatives of the genus, but the fading away of its 

 narrow, undulating flank costae on the posterior part of the flank, its smooth poste- 

 rior area, and its ill-defined marginal carina are exactly as in such species as R. 

 excentrica (Parkinson) (figured Lycett, 1875 : 94, pi. 20, figs. 5, 6 ; pi. 21, figs. 6, 7 ; 

 pi. 22, figs. 5, 5«) and R. laeviuscula (Lycett) (1875 : 96, pi. 22, fig. 6). 



Genus OPISTHOTRIGONIA Cox 1952 



Opisthotrigonia carta (Aitken) 

 PI. 12, fig. 4 

 1 961. Laevitrigonia curta Aitken : 97, pi. 14, figs. 1-3. 



Material. Two specimens (including no. LL.35112), ex B.P. Coll. 



Locality and horizon. Mpilepile stream, 800 yards E.N.E. of junction of main 

 road and Mahokondo road, Mitole, northern Mandawa area, Tanganyika ; Upper 

 Kimmeridgian. 



Remarks. Prior to the publication of Aitken's paper, these specimens had been 

 described in MS. as a new species of Opisthotrigonia. One which is 43 mm. long and 

 considerably larger than any of Aitken's specimens is here figured to illustrate the 



