FROM TANGANYIKA AND KENYA 113 



straight, subhorizontal, forming an obtuse angle with the straight, slightly oblique 

 posterior margin ; ventral margin almost straight ; antero-dorsal outline strongly 

 concave ; anterior margin strongly convex. An obtusely rounded ridge, curved 

 with an upward-facing convexity, runs from the umbo to the postero-ventral corner 

 in each valve. Pallial line entire. 



Holotype. No. LL. 35058. There are also two very imperfect specimens. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. The specimens are internal moulds and details of their hinge-structure 

 cannot be ascertained. The species is referred, with a query, to Eotrapezium because 

 its subrectangular outline resembles that of some specimens of the Lower Liassic 

 type species, Mesodesma germari Dunker, such as those from Portugal figured by 

 Boehm (1901, pi. 10, figs. 6, 7). Alternatively, it could conceivably belong to the 

 Astartidae, but its strongly excavated antero-dorsal outline and greater inflation 

 distinguish it from known species of the astartid subgenus Leckhamptonia, in which 

 the rectangular outline of the shell is somewhat similar. No closely comparable 

 species has been described previously from the Upper Lias. 



Eotrapezium ? thompsoni sp. nov. 

 PI. 18, figs. 2a, b 



Specific name. After Mr. A. O. Thompson, of the Kenya Geological Survey, 

 collector of the type material. 



Diagnosis. Of small-medium size (length 17 mm.), trapeziform, inequilateral, 

 length not greatly exceeding height, beaks at anterior quarter of length ; inflation 

 rather weak (but holotype somewhat crushed). Umbonal outline obtuse, umbones 

 scarcely incurved ; postero-dorsal outline feebly convex, subhorizontal, forming an 

 obtuse angle with the straight, slightly oblique posterior margin ; ventral margin of 

 feeble convexity, diverging slightly from postero-dorsal outline in a posterior direc- 

 tion ; antero-dorsal outline moderately concave ; anterior margin strongly convex. 

 An obtusely rounded ridge, curved with an upward facing convexity, runs from the 

 umbo to the postero-ventral corner. Surface ornamented with concentric threads. 



Holotype. No. LL. 35061. There is also one very imperfect specimen. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya. 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. This species bears a general resemblance to Eotrapezium? africanum, 

 described above, but differs in its much shorter form. 



Eotrapezium ? kenti sp. nov. 

 PI. 18, figs, ga, b, 10a, b 



Specific name. After Dr. P. E. Kent, of the British Petroleum Company, Ltd. 

 Diagnosis. Shell of medium size (length of holotype c. 27 mm.), ovate-cuneiform, 



