144 JURASSIC BIVALVIA AND GASTROPODA 



Holotype and paratypes. Nos. GG.10258 and GG.10259-62 respectively, five 

 specimens in all. 



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

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. The characters of the inner lip of this species agree with those of 

 Trochopsidea, the presence of the groove on the outer face of this lip distinguishing 

 the species from representatives of Ataphrus, which it resembles in its general 

 morphology. Turbo garnieri Dumortier (1874 : 139, pi. 35, figs. 15-17), from the 

 Upper Lias of southern France, which much resembles the present species except 

 that it is slightly more elevated, has not a grooved inner lip and appears to belong to 

 Ataphrus (Endianaulax). A specimen from the Upper Lias of Germany identified by 

 Kuhn (1935 : 136, pi. 8, fig. 21) as Ataphrus cf. lucidus (Thorent) (a species included 

 by Cossmann in the subgenus Endianaulax) is more depressed than the present form. 



Superfamily NERITACEA 



Family NERITIDAE Rafinesque 1815 



Genus NERITOMA Morris 1849 



Subgenus NERIDOMUS Morris & Lycett 1851 



Neritotna (Neridomus) aff. gea (d'Orbigny) 

 PI. 24, figs, ya, b 



1852. Aff. Nerita Gea d'Orbigny : 232, pi. 302, figs. 5-7. 



1885. Aff. Nerita Gea d'Orb. ; Cossmann : 155, pi. 3, figs. 1, 2. 



1908. Aff. Nerita gea d'Orbigny ; H. Fischer : 268, pi. 11, figs. 5-12. 



Material. Three specimens (nos. G.61310-12). 



Locality and horizon. S. of Tarawanda, 26 miles W.S.W. of Bagamoyo, 

 Tanganyika ; Callovian. 



Remarks. The specimens now recorded, the best of which is just under 10 mm. 

 in height and diameter, are characterized by their low spire, obtusely rounded apex, 

 and flush sutures. The apex and axis are rather strongly eccentric. The speci- 

 mens belong to a group of species which is well represented in the Bathonian of 

 Europe and has been discussed by H. Fischer (1908). They seem to be very closely 

 comparable to Neritoma (Neridomus) gea, but they are a little larger than the 

 specimens figured by the authors cited above, and their axis is more eccentric. 

 They are also rather similar in shape to N. (N.) louisiae Fischer (1953 : 15, pi. 1, 

 figs. 21-27), also from the French Bathonian, but that species attains a much 

 larger size (20 mm.) and has a more pointed apex. Cossmann (1926 : 305, pi. 5, 

 figs, la-c) has recorded a specimen of the same group from the Callovian of Sinai 

 under the name Neridomus punctatus (Piette), but it is also considerably larger 

 than the specimens now recorded. The species Neritodomus sukidugallensis Reck 

 (1921 : 435, text-fig. 3) was founded on a small broken shell from the Bajocian 



