212 Geological Society. 



LiMicoLAEiA eectisteigataE. A.Smith. Locality. — Archer's 

 Post. 



Distribution. — Recent: Rudolf and Tanganyika regions. 



Rhachis ehodot^kia Martens. Locality. — Chukali Grhofu. 

 Distribution. — Recent: Victoria Nyanza and Mount Kenya 

 plateau. 



Leptospatha spathuliformis (Bourguignat). Localities. — 

 Turbi and Lak Buna. 



Distribution. — Recent: Rudolf and Zanzibar. 



CoRBicFLA FLUMiisrALis (Miiller) (= saha7'ica Fischer). 

 Localities. — Turbi; Lak Buna and Chukali Ghofu. 



Distribution. — Recent: Nile, Rudolf, Marguerite, and 

 Abyssinia ; Post-Pliocene: Egypt and Sahara ; Pliocene: 

 French Somaliland ; Miocene : Rudolf (Omo-River beds). 



CoRBiCFLA EADiATA {^pusUla?) Philippi. Locality, — 

 Chukali Ghofu. 



Distribution. — Recent: Nile, Rudolf, Victoria Nyanza, 

 Albert Edward, Nyasa, Tanganyika; Post-Pliocene: Egyjjt ; 

 Pliocene: French Somaliland; Miocene: Rudolf (Omo-River 

 beds). 



No vertebrates occurred with these shells, hence their age Avould 

 probably be younger than the Omo-River deposits north of Lake 

 Rudolf, that have yielded a somewhat similar moUuscan fauna, 

 but with the addition of Dinotlierium and other vertebrate remains. 

 The presence of that genus, as pointed out by Dr. Haug ('Traite 

 de Geologic' 1908-11, vol. ii, p. 1727), was indicative of the 

 Pontian or Upper Miocene Period. There are, however, some 

 lacustrine beds near Lake Assal, in French Somaliland (formerly 

 regarded as Abyssinia), which contain shells also bearing a resem- 

 blance to those collected by Mr. Parkinson in British East Africa, 

 especially Melania tiiberculata, Cleopatra hidimoides, Corhicula 

 fluminalis, and O. radiata, which are common to both sets of 

 deposits. These Lake Assal beds, which are also without vertebrate 

 remains, have been identified by Aubry (Bull. Soc. Geol. France, 

 ser. 3, vol. xiv, 1885, pp. 206-209), and Pantanelli (Atti Soc. 

 Toscana Sci. Nat. Proc.-verb. vol. v, 1887, pp. 204-206, and ibid. 

 vol. vi, 1888, p. 169) as of Pliocene age. If, from these facts, such 

 widely distant beds can be recognized as contemporaneous, then 

 the suggestion may be made that the northern half of British East 

 Africa was probably an extensive freshwater region during Pliocene 

 times, limited on the north by Lake Assal, on the east by Suddidima, 

 on the south by Archer's Post and the Mount Kenya plateau, and 

 on the west by Lakes Rudolf, Stefanie, and Marguerite. 



Assistance in the determination of these shells had been kindly 

 rendered by Mr. E. A. Smith, I.S.O. 



