n6 JURASSIC BIVALVIA AND GASTROPODA 



Eomiodon dinosaurianum sp. nov. 

 PI. 18, figs. 15a, b, 16a, b 



1933. Cyrena sp. ; Dietrich : 46, pi. 8, fig. 125 ; ? pi. 11, fig. 147. 



Diagnosis. Shell small (usual length c. 12 mm.), trigonally ovate, variable in 

 proportions but always longer than high, subequilateral to moderately inequilateral, 

 with beaks lying between a position slightly posterior to median and the anterior 

 quarter of the length ; inflation moderate (most specimens, however, are crushed). 

 Umbo broadly rounded, slightly incurved to the moderately prosogyrous beak, its 

 outline continuous with straight postero-dorsal outline of shell ; postero-dorsal 

 outline sloping at a moderately steep angle to meet the usually short, straight 

 posterior margin in an obtuse angle ; ventral margin convex to a variable extent, 

 merging in an even curve with the strongly convex anterior margin ; antero-dorsal 

 outline slightly concave. Escutcheon moderately wide, bordered by well-defined 

 ridges ; lunule somewhat excavated, not bordered. A rather obscure diagonal ridge 

 runs from the umbo to postero-ventral corner of shell. Ornament consisting of thin 

 concentric ridges which fade away at a variable distance from the umbo, so that 

 later growth-stages are smooth in all full-grown specimens ; ridges separated by 

 much broader intervals. 



Holotype and paratypes. Holotype, no. L. 53322. There are also numerous 

 paratypes. 



Locality and horizon. Tendaguru, Tanganyika ; excavation in Upper Kim- 

 meridgian, dinosaur beds. 



Remarks. The specimens are preserved in fine-grained buff-coloured sandstone. 

 The great amount of variation which they show appears to be largely due to original 

 differences in shape, although many have suffered distortion and compression in 

 fossilization. The species is not closely comparable to any previously described 

 from the Upper Jurassic. E. nortonensis (Cox) (1944& : III, text-fig. 4c), from the 

 Lower Bathonian of England, is of about the same size as the East African species, 

 but differs in its cuneiform and more elongate shape. 



Eomiodon namgaruensis sp. nov. 

 PL 18, figs. 14a, b 



Diagnosis. Rather large for the genus (length of holotype 49 mm.), ovate- 

 cuneiform, inequilateral, height about four-fifths of length, beaks at anterior fifth 

 of length ; inflation strong. Umbo prominent, very broadly rounded, well incurved 

 to the strongly prosogyrous beak. Postero-dorsal outline pronouncedly parasigmoi- 

 dal, rather steep, forming an obtuse angle with the low, straight, oblique posterior 

 margin ; ventral margin strongly convex ; antero-dorsal outline strongly concave ; 

 anterior margin broadly convex. Escutcheon moderately wide, well impressed, 

 bordered by sharp ridges ; lunule broad, cordate, well impressed, smooth, also 

 bordered by a ridge in each valve. No distinct ridge runs from the beak to the 



