166 ON EIYEH-CRABS OF TILE GENUS THELPHUSA. [Mar. 6 



Dr. Gregory then exhibited and made remarks upon a series 

 of photographic slides, illustrative of his recent expedition to 

 Mount Kenia. 



The following papers were read : — 



1. Note on Three Species of River-crabs of the Genus Thel- 

 phusa, from Specimens collected in Eastern Africa 

 by Dr. J. W. Gregory, Mr. H. H. Johnston, C.B., and 

 Mr. F. J. Jackson. By F. Jeffrey Bell, M.A. 



[Received February 7, 1894.] 



During his remarkable expedition to Mount Kenia Dr. Gregory 

 obtained, in the papyrus-swamp north of Rangatan Ndari, Lei- 

 kipia, a River-crab of the genus Thelphusa, which may be referred 

 to the species T. berardi, first figured by Savigny. From a 

 height of from two to three thousand feet on Mount Zomba, 

 Mr. H. H. Johnston, C.B., has lately sent a specimen which must 

 be referred to T. depressa, Krauss. Mr. F. J. Jackson has also 

 been so good as to present to the Trustees of the British Museum 

 two examples of the same genus taken on the south side of Mt. 

 Elgon, which are to be referred to T. nilotica, M.-E. 



It is very interesting that three different species should reach 

 the Museum within as many months from three distinct, though 

 not so very distant, localities in the eastern half of Central Africa. 

 What is of importance is that the species from the more northern 

 localities (Mt. Elgon aud Leikipia) are those which have a more 

 northern distribution, for both are Egyptian ; whereas T. depressa 

 was described by Krauss * from Port Natal, and a variety of the 

 same species, characterized by Mr. E. J. Miers 2 as T. depressa 

 johnstoni, was found by Mr. H. H. Johnston during his expedition 

 to Kilimanjaro in 1884. 



So far as evidence is afforded by the species of this freshwater 

 Crab, the line of demarcation between North and South Africa 

 would lie south of Mt. Elgon and north of Kilimanjaro ; and in 

 support of this view there is the fact that, as Mr. Edgar Smitb has 

 reminded me, Physopsis afrieana and Limncea natalensis, which 

 were both described by Krauss from specimens collected in Natal, 

 have been found in Lake INYassa. The latter, however, extends as 

 far north as Abyssinia, and there is some reason to suppose that it 

 also inhabits the West Coast of Africa ; so that it does not afford 

 us much assistance in the delimitation of areas of distribution in 

 this region of the African continent. 



However, the problems of distribution in Africa are so many and 

 so difficult, that what we need at present is a broader and firmer 

 basis of facts. 



1 Siidafrikan. Crust. (1843), p. 38, pi. ii. fig. 4. 

 3 Proc. Zool. Soc. 1885, p. 237. 



