FROM TANGANYIKA AND KENYA 117 



postero-ventral corner of the shell. Early growth-stages ornamented with narrow, 

 regular concentric ridges of which those farthest from the umbo are about 1 mm. 

 apart ; remainder of shell with only irregular concentric rugae. 



Holotype and paratype. Holotype, no. LL.35146 ; one broken paratype. 

 Both ex B.P. Coll. 



Locality and horizon. About 1 mile E.S.E. of Uleka, Mavudyi-Namgaru area, 

 Tanganyika ; Jurassic (stage uncertain). 



Remarks. The dimensions of this shell, which has the unmistakable external 

 characters of Eomiodon, exceed those of any previously known Jurassic species of the 

 genus, but are less than those of E. libanotica (Fraas) (Vokes, 1946 : 172, pi. 5, figs. 

 1-12, as Protocyprina libanotica) from the Aptian of the Lebanon. 



Subgenus AFRICOMIODON nov. 



Diagnosis. Well inflated, with anteriorly placed, prominent, strongly proso- 

 gyrous and incurved umbones. Escutcheon broader than in Eomiodon s.str. and 

 bordered by ridges which are not so well defined as in that group ; in each valve one 

 cardinal tooth (26 in the left, 36 in the right) is stoutly triangular, but remaining 

 cardinals only feebly developed. Anterior lateral (Aii) in left valve and posterior 

 lateral (Pi) in right valve strongly developed, remaining laterals weak. 



Type species. Eomiodon (Africomiodon) cutleri sp. nov. 



Remarks. This new subgenus resembles Eomiodon s.str. in the general arrange- 

 ment of the hinge teeth and in the presence of evenly spaced concentric ridges which 

 are confined to earlier growth stages. It is distinguished by the very different shape 

 and strong inflation of the shell and by the weakness of all the teeth except the four 

 mentioned. 



Eomiodon (Africomiodon) cutleri sp. nov. 

 PI. 18, figs. 17, 18a, b 



Specific name. After the late W. E. Cutler, the first leader of the British Museum 

 East Africa Expedition. 



Diagnosis. Shell of medium size, with characteristic asymmetrical outline due 

 to pronounced postero-dorsal angle and rather protruding, very anteriorly placed, 

 prosogyrous umbones ; height (20-5 mm. in holotype) slightly exceeding length in 

 most specimens. Postero-dorsal outline convex, gently sloping, forming rather pro- 

 nounced, obtuse angle with feebly convex posterior margin ; this merges into the 

 strongly and evenly convex ventral margin which is continued by the equally con- 

 vex anterior margin, the two forming almost a semicircle ; antero-dorsal outline 

 strongly excavated. The evenly spaced, well separated concentric ridges present 

 in early growth stages (where they are particularly prominent on the posterior part 

 of the surface) soon give way to the unevenly arranged concentric threads and rugae 

 which occupy the greater part of the surface. Dentition as described in the sub- 



