148 JURASSIC BIVALVIA AND GASTROPODA 



Pseudomelania dusseensis sp. nov. 

 PI. 24, figs. 11a, b, c 



Diagnosis. Shell small (height about 11 mm.), regularly conical, moderately 

 acute (spire angle about 16 °), with the spire formed of rather low, very feebly convex 

 (virtually flat) whorls, separated by flush sutures ; height of spire whorls equal to 

 about one-half of their diameter. Last whorl abruptly rounded, almost angular at 

 periphery ; base low, feebly convex, without umbilicus. Aperture broader than 

 high ; outer lip flat or very feebly convex ; columellar lip short. Surface smooth ; 

 growth-lines, where faintly visible, arched, with a shallow forward-facing concavity. 



Holotype and paratypes. Nos. 0.76399 and G.76400-02 respectively, four 

 specimens in all. 



Locality and horizon. Low hills at Dusse, ij miles S.E. of Rahmu, N.E. 

 Kenya ; Upper Oxfordian, Seir Limestones. 



Remarks. This species closely resembles Pseudomelania communis (Morris & 

 Lycett) (1851 : 48, pi. 9, figs. 21, 21a), from the English Bathonian, but is distin- 

 guished by its flatter whorls. P. laubei Cossmann (1885 : 176, pi. 11, figs. 32, 33 ; 

 pi. 15, fig. 47), from the Bathonian of France, is a larger shell (25 mm. high), with 

 slightly higher whorls. In the French Callovian species P. calloviensis (Hebert & 

 Deslongchamps) (Couffon 1919 : 126, pi. 8, figs. 19-19^ ; Cossmann 1924 : 4, pi. 1, 

 figs. 21-23) the whorls are relatively higher. P. calloviensis has axial riblets on its 

 earliest formed whorls and therefore belongs to the subgenus Hudlestoniella Coss- 

 mann. As the corresponding whorls are missing on the specimens now described it 

 is not possible to say if the species should be included in that subgenus rather than in 

 Pseudomelania s. str. Of European Oxfordian species, P. ebersteini (Thurmann) (de 

 Loriol 1899 : 133, pi. 9, fig. 20), from the Swiss Jura, is a broader shell than the form 

 now described and has more strongly convex whorls. 



Pseudomelania vittata (Phillips) 

 PI. 24, fig. 12 



1829. Melania vittata Phillips : 145, pi. 7, fig. 15. 



1863. Chemnitzia vittata (Phil.) ; Lycett : 14, pi. 31, fig. 10. 



1882. Chemnitzia vittata (Phil.) ; Hudleston : 244, pi. 6, figs. 5a, b, 6. 



1905. Pseudomelania vittata (Phil.) ; Blake : 77, pi. 8, figs. 1, 2. 



1950. Pseudomelania vittata (Phillips) ; Cox & Arkell : 62. 



Material. One specimen (no. GG.10316). 



Locality and horizon, i mile N. of Manyuli, Tanganyika ; Upper Kim- 

 meridgian. 



Remarks. Pseudomelania vittata is a large form characterized by the presence 

 on the last whorl of two strong but obtuse keels, between which the face of the shell 

 is slightly concave. On the spire whorls the upper keel lies at about the posterior 

 third of the height, while the lower keel may or may not be visible near the lower 

 suture, according to the degree of whorl overlap. I am unable to distinguish the 



