FROM TANGANYIKA AND KENYA 155 



species with which the present one could be brought into comparison. Z. subrugosa 

 McDonald & Trueman (1921 : 330, text-fig. 18), from the Upper Lias of Grantham, 

 Lincolnshire, resembles the East African species in its angular whorl profile and does 

 not greatly exceed it in height, but it is a less acute shell, the periphery of its whorls is 

 much more protruding, and the number of costae on each whorl is greater. 



Superfamily LITTORINACEA 



Family PURPURINIDAE Zittel 1895 



Genus PURPUROIDEA Lycett 1848 



Purpuroidea supraliasica sp. nov. 

 PI. 28, figs. 4a, b 



Diagnosis. Shell rather small for the genus (height of largest specimen c. 30 

 mm.), conical-ovate, diameter two-thirds of height, spire elevated, acute, occupying 

 up to one-half of total height. Whorls with almost flat sides, slightly convergent 

 adapically, separated from narrow sutural ramp by shoulder bearing large rounded 

 tubercles. Base extended, slightly convex in outline, and limited by an obtuse, 

 rounded-off angulation that continues the line of the suture. Parietal lip straight, 

 oblique, with a narrow, distinctly margined layer of callus, and joining the apparently 

 very short columellar lip (not preserved complete in the available specimens) in an 

 obtuse angle. Outer lip not preserved in the available specimens, in which any finer 

 ornament that may have been present has been obliterated by erosion. 



Holotype and paratypes. Nos. GG.10264 and GG.10265-69 respectively, six 

 specimens in all. 



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

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. This shell is comparable in shape to the much larger species Purpuroi- 

 dea berberica Dubar (1948 : 94, pi. 7, figs. 6-8), from the Middle Lias of Morocco, 

 and has a similar tuberculate shoulder to its whorls. Its base, however, is more 

 extended than in that species. 



Purpuroidea aff. gigas (Thurmann & Etallon) 

 PI. 26, fig. 2 ; PI. 27, fig. 15 



1861. Aff. Purpura gigas Thurmann & Etallon : 138, pi. 13, fig. 121. 



1874. ?Aff. Purpurina subnodosa (Roemer) ; Brauns : 169 (non Natica? subnodosa Roemer). 



1881. Aff. Purpuroidea gigas (Etallon) ; Schlosser : 68, pi. 10, figs. 4, 4a. 



1909. ?Aff. Purpuroidea subnodosa (Roemer) ; Brosamlen : 251 {non Roemer sp.). 



Material. One specimen (no. GG. 10328). 



Locality and horizon, £ mile N.W. of Mbinga, Tanganyika ; Upper Kim- 

 meridgian. 



