556 DR. W. A. CUNNIKGTON ON THE 



obtained in Victoria Nyanza by Stuhlmann in 1890 (100, p. 36), 

 It was re-taken in the lake by Neumann, and more recently by 

 Alluaud, by myself, and by Degen. From Nyasa a species of 

 prawn was brought for the first time by m}'^ expedition. These 

 species prove to be one and the same form — the Caridina nilotica 

 var. gracilipes, to which reference has just been made. During 

 the German Central Africa Expedition of 1907-08 this prawn 

 was collected by Schubotz in both Lakes Albert * and Edward 

 (109, p. 130). It is thus the only common species in the African 

 lakes, while it has in fact a yet wider distribution, ranging in 

 Africa from Natal to the Nile and extending into Asia and 

 Australia. The eastwa,rd range of this type has indeed an 

 additional interest on account of the well-marked resemblance 

 noticeable in other groups between the East African and Indian 

 faunas. 



Only tlie fii'st of the twelve species enumerated from Tangan- 

 yika can be compared at all closely with forms which are known 

 from other jjarts of the Avorld, and it has no very pronounced 

 affinities. The remaining eleven species belong to the group of 

 the Atyidas, and are not so nearly connected with tj-pes hitherto 

 known. Moreover, in common with Liinnocaridella alherti, they 

 differ from all the other species of the family in having a smaller 

 number of branchiae f, which is a feature undoubtedly due to 

 specialisation. 



To sum up then, there occurs in most of the great lakes of 

 Africa only a single species of prawn having a very wide 

 distribution. In Lake Albert this is associa'ted with an endemic 

 form, and in Tanganyika it is i-eplaced by twelve other endemic 

 forms, the majority of which are among the most highly sj^ecial- 

 ised members of the family to which they belong. Under the 

 circumstances, it is impossible to resist the suggestion that there 

 is exhibited here something very similar to what was seen in the 

 case of the fishes, and particulai'ly the Cichlidse. If the extra- 

 ordinary variety of form, and high degree of specialisation, which 

 is characteristic of the Cichlids of Tanganjdka, may have been 

 due to prolonged isolation and comparative freedom fi-om com- 

 petition, it at least seems not improbable that the rema,rkable 

 Macruran fauna of the lake owes its origin' to the same cause J. 



Brachyuka. 



There are five different species of crabs now known from 

 Tanganyika, of which one has been left unnamed for the present. 

 In a manner closely corresponding with the case of the prawns, 



* See footnote above. 



f A. reduced branchial formula is also characteristic of the remarkable West 

 Indian form for which Bouvier has established the genus Micrati/a (51, p. 181), 

 formerly Cahnania (50, p. 334). Bouvier regards this as allied to the Tanganyikan 

 genera, but this view is not accepted by Caiman (62, p. 796). 



X An important paper dealing with the origin of the peculiar prawn fauna of 

 Tanganyika was communicated by Bouvier to the International Zoological Congress 

 at Monaco (52). Consult also Bouvier's paper on the classification of the Atyidse 

 (51). 



