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Show 166 ON RIVER-CRABS OF THE 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 Biver-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 Bangatan Ndari, Lei-kipia, a Biver-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. P. 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 and Leikipia) are those which have a more northern distribution, for both are Egyptian; whereas T. depressa was described by Kraussl 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 Smith has reminded me, Physopsis africana and Limncea natalensis, which were both described by Krauss from specimens collected in Natal, have been found in Lake Nyassa. 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. 2 Proc. Zool. Soc. 1885, p. 237. |