FROM TANGANYIKA AND KENYA 35 



Family ARCIDAE 

 Genus EONAVICULA Arkell 1929 



Eonavicula sp. " A " 



PL 2, figs. 8a, b 



Material. One specimen (no. L. 92046). 



Locality and horizon. Muddo Erri, 12 miles W. of Rahmu, N.E. Kenya ; 

 Callovian [?-Lower Oxfordian], Muddo Erri Limestones. 



Description. This specimen is 31-5 mm. long, well elongated and strongly in- 

 equilateral, with the umbo at about the anterior quarter of the length. The sym- 

 metrically arched ventral margin is almost flat in the middle ; the growth-lines show 

 that it had a shallow median sinus at an earlier stage of growth. The well-marked 

 posterior carina has a gentle upward-facing concavity and borders a posterior area on 

 which the internal mould has one conspicuous radial sulcus and traces of at least one 

 other above it. Although mainly an internal mould, the specimen retains a few 

 portions of the original shell on which well-marked growth-rugae are crossed by fine 

 radial threads. 



Remarks. This specimen, which has the general appearance of an Eonavicula 

 although its hinge-structure is not seen, is more strongly inequilateral than the 

 Bathonian species E. minuta (J. de C. Sowerby), the best figure of which, published 

 by Morris & Lycett (1853, pi. 5, fig. 17), is misidentified as Area aemula. The 

 Oxfordian (Corallian) species E. quadrisulcata (J. de C. Sowerb}') (Arkell, 1929a, pi. 1, 

 figs. 3-5) is less elongate and inequilateral, and has four sulci on its posterior area. 

 The Kimmeridgian species E.fracta (Goldfuss) (1837 : 141, pi. 121, figs. 10a, b) is as 

 elongate as the present specimen but is not quite so strongly inequilateral, while, 

 according to Goldfuss's figure, its posterior area is without sulci. The specimen now 

 described may thus belong to a new species, but it seems undesirable to assign a name 

 to it as it retains so little of its shell. 



Eonavicula sp. " B " 

 PL 3, fig. 2 



Material. One specimen (no. LL.11517). 



Locality and horizon. Kindope, N.N.W. of Tendaguru, Tanganyika ; Upper 

 Kimmeridgian, Nerinella Bed. 



Description. This specimen, an internal mould, is 22-5 mm. long, well elonga- 

 ted, and moderately inequilateral, with the umbo at about the anterior third of the 

 length. The whole of the posterior half of the ventral margin forms a broad sinus. 

 The well-marked posterior carina has a gentle upward-facing concavity, and above 

 it are two radial sulci. 



Remarks. This specimen differs from the equally elongate Eonavicula sp. " A " 

 in the more anterior position of its umbo and in the broad sinus of the posterior part 



