FROM TANGANYIKA AND KENYA 137 



Loriol) (1878 : 141, pi. 22, figs. 2, 3) or in the two Tithonian species C. picteti (Zittel) 

 (1870 : 118, pi. 12, fig. 7) and C. transylvanica (Neumayr) (1873 : 205, pi. 43, fig. 5) ; 

 in consequence, the posterior margin has a well-defined sinus. These are the two 

 most closely comparable species described previously. 



Class GASTROPODA Cuvier 



Subclass PROSOBRANCHIA Milne Edwards 



Superfamily EUOMPHALACEA 



Family EUOMPHALIDAE de Koninck 1881 



Genus DISCOHELIX Dunker 1848 



Discohelix didimtuensis sp. nov. 

 PI. 22, figs. la, b, c, d 



Diagnosis. Rather small (diameter of largest specimen 10-5 mm.), discoidal, 

 compressed, upper face flat, lower face umbilicate. Outer face low, slightly concave, 

 inclined inwards to a slight extent in an abapical direction, and separated from upper 

 face and from base by tuberculate carinae which project in an abaxial direction. 

 Some tubercles of both carinae are elongated transversely, so that on both the upper 

 face and the base they remain partly visible along the outer suture on the earlier 

 whorls, and in some specimens they are continued across the upper face of these 

 whorls by weak transverse riblets. The entire surface of the shell is ornamented with 

 delicate spiral threads. 



Holotype AND paratypes. Nos. GG.10246 and GG. 10247-49 respectively, four 

 specimens in all. 



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

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. In Discohelix dunkeri Moore (1867 : 85, pi. 5, figs. 28, 29 ; also 

 Dumortier 1874 : 141, pi. 35, figs. 18, 19), from the Upper Lias of southern England 

 and France, the ornament of the shell is closely comparable to that of the new species, 

 but the two carinae are less prominent and, between them, the outer face of the shell 

 is feebly convex ; transverse riblets originating at the tubercles are well marked on 

 both the upper face and the base. D. sinistra (d'Orbigny) (1853 : 310, pi. 322, figs. 

 1-7), from the Middle Lias of France, differs in much the same manner. D. albinati- 

 ensis Dumortier (1874 : 284, pi. 59, figs. 3-5 ; also Kuhn 1935 : 132, pi. 10, fig. 5), 

 from the Upper Lias of France and Germany, much resembles the new species, but 

 the lower of its two carinae projects abapically instead of outward, and the outer face 

 of the shell is convex rather than concave. 



