128 JURASSIC BIVALVIA AND GASTROPODA 



not here accepted. Although radial ornament is relatively weak and variable in 

 P. ovalis, it is more distinct than in any specimens which have been recorded as P. 

 inornata, a species which it seems preferable to include in Homomya. The African 

 fossil now recorded is imperfect, but agrees well with typical specimens from India. 



Homomya rahmuensis sp. nov. 

 PL 20, figs. 3a, b 



i960. Homomya sp. nov. ; Joubert, pi. 11, figs, ga, h. 



Diagnosis. Small for the genus (length of holotype 43 mm.), oblong-ovate, 

 height about three-fifths of length ; inflation moderate (22 mm. in holotype) and 

 even, greatest at about mid-length ; posterior gape narrow. Umbones rather 

 narrow, protruding only slightly, placed at about the anterior fifth of the length ; 

 posterior umbonal ridge, bordering a rather broad but shallow escutcheon, ill-defined 

 except near the umbones. Postero-dorsal and ventral margins straight, elongate, 

 sub-parallel. Posterior margin of feeble convexity, sub-vertical in its general direc- 

 tion. Ornament consisting of weak, irregular concentric folds. 



Holotype. No. L. 92260. The only specimen. 



Locality and horizon. Uacha, 6 miles S. of Rahmu, N.E. Kenya. Oxfordian, 

 Rahmu Shales. 



Remarks. This species is comparable to H. censoriensis (Cotteau) (Peron, 1906 : 

 43, pi. 1, fig. 1), Oxfordian of France, but is not so high at its posterior end. H. 

 corallina de Loriol (1894a : 80, pi. 6, figs. 1, la), Lower Kimmeridgian of France, is 

 more gibbose and slightly less elongate. 



Homomya hortulana Agassiz 

 PL 20, fig. 4 



1843. Homomya hortulana Agassiz : 155, pi. 15. 



1872. Pholadomya hortulana (Agassiz); de Loriol : 166, pi. 10, fig. 16. 



1893. Pholadomya (Homomya) hortulana (Agassiz) ; Choffat : 33, pi. 9, figs. 2-6. 



1933. Homomya cf. hortulana Agassiz ; Dietrich : 55, pi. 7, fig. 104. 



Material. Three specimens. 



Localities and horizons. N. of Kipande, Tendaguru, Tanganyika ; Upper 

 Kimmeridgian, Nerinella Bed. Mtapaia road, Tendaguru ; Upper Kimmeridgian, 

 " Trigonia smeei " Bed. 



Remarks. The prominence of the umbones varies considerably in European speci- 

 mens of this species. They are very broad and depressed in the East African speci- 

 mens now recorded, but these can be matched with published figures of specimens 

 from Europe, and it seems unnecessary to follow Dietrich in qualifying their specific 

 identification. 



