FROM TANGANYIKA AND KENYA 151 



weaker than the collabral rugae. Another comparable European species is P. 

 collisa de Loriol (1874 : 334, pi. 7, figs. 30, 31), from the Lower Kimmeridgian of 

 France, but its whorls are slightly more convex than those of the form now described. 



Pseudomelania {Oonia) aitkeni sp. nov. 

 PL 25, figs, ia, b, c 



Specific name. After Dr. W. G. Aitken, lately Director of the Geological 

 Survey of Nyasaland, and collector of the holotype. 



Diagnosis. Shell of medium size (height of holotype c. 22 mm.), ovate-conical, 

 with diameter equal to about one-half of height. Spire slightly coeloconoid, with 

 very acute apex. Spire whorls low, their mean height rather less than one-third of 

 their diameter, feebly convex, the later ones with a narrow, ill-defined sutural ledge. 

 Last whorl broadly and evenly convex at periphery, outline of base scarcely exca- 

 vated ; no umbilicus. Aperture oval, originally occupying about one-half of total 

 height of shell (its margin, however, is broken away in the holotype). Surface 

 smooth. 



Holotype. No. GG.10318. The only specimen. 



Locality and horizon. Along Mandawa-Namakongoro stream, about 1 mile 

 W. of Mandawa, Tanganyika ; Middle-Upper Kimmeridgian. 



Remarks. As the apertural margin is broken away in the holotype it is not 

 possible to observe if (as in the Pseudomelaniidae) it was uninterrupted anteriorly 

 or if (as in some Coelostylinidae) a small notch or sinus was present at the foot of the 

 columella. The species is here referred to the pseudomelaniid subgenus Oonia, from 

 the typical species of which it differs in its aciculate apex. It is of about the same 

 size and proportions as Pseudomelania (Oonia) recki Dietrich (1914 : 130, pi. n, 

 figs. 16a, b), from Tendaguru, but is readily distinguished by its coeloconoid spire 

 and more numerous and flatter whorls. In P. (0.) cornelia (d'Orbigny) (1851 : 60, 

 pi. 245, figs. 2, 3), from the " Corallian " of the Ardennes, and in P. (0.) quirandi de 

 Loriol (1887 : I 45> P 1 - I 5. n g s - 5- °)> from the Lower Kimmeridgian of Valfin (Jura), 

 the spire is slightly cyrtoconoid and the last whorl is less inflated. P. (0.) daphne 

 de Loriol (1890 : 87, pi. 11, fig. 6), from the Upper Oxfordian of the Bernese Jura, 

 is a smaller shell. 



Subgenus RHABDOCONCHA Gemmellaro 1878 



Pseudomelania (Rhabdoconcha) wilder riensis sp. nov. 

 PL 25, fig. 10 



i960. Pseudomelania valfinensis de Loriol ; Joubert, pi. 11, fig. 13& (non de Loriol). 



Diagnosis. Shell large (original height of holotype c. 120 mm.), acute (spire 

 angle 12 °), with feebly and evenly convex whorls the height of which is about three- 

 quarters of the diameter ; last whorl broadly convex at periphery. Surface orna- 



