FAUNA OP THE AFRICAN LAKES. ODo 



Tanganyika with 14 endemics out of 17 leads the way as far 

 as endemic Lamellibranchs are concerned (82 per cent.), Lake 

 Victoria coming near with 12 out of 18 (66 per cent.), while 

 jSTyasa has 7 out of 13 (54 per cent.). Even the smaller lakes 

 have each two endemic species. It will be observed that the 

 proportion of peculiar forms is very high in tins group also ; 

 indeed, in some instances it is higher than in the case of the 

 Gasteropoda. Endemic genera are known only from Tanganyika, 

 three being retained in the list out of a larger number distiii- 

 guisbed by Bourguignat. The genus Moncetia of Bourguignat, 

 inserted in the table as endemic, though not deiinitely rejected, 

 is nevei'theless considered by Smith as only doubtfully separable 

 from Spatha (170, p. 101). 



A brief survey of the list of species will suffice. Corhicula 

 radiata, a representative of the Cja-enidas, is the only form which 

 is on record from all the lakes concerned. It is a widely disti-i- 

 buted African type, being known fi-om other parts of East Africa 

 and from the valley of the Nile. — The familj'^ Splueriidfe is 

 represented by the genera Sphcerium and Eujyera. It is some- 

 what strange that the four species enumerated are all found in 

 Lake Victoria, but not in Tanganyika or Nyasa. Sphterium 

 nyanzce is knox^n from Victoria, Albei-t and Edward Nyanzas, as 

 well as from other parts of the continent, but it is associated in 

 Victoria with two additional species which are peculiar to that 

 lake. Eupera parasitica, which is a Nilotic and IST. African form, 

 is at present only recorded from Victoria Nyanza. — In the family 

 Unionidee there are associated with the extensive genus Unto 

 itself only the two closely related genera Burtonia and Brazzcea, 

 which are confined to Tanganyika. No fewer than 29 different 

 species of Unio are enumerated, not one of which is on record 

 from more than a single lake. Tanganyika exhibits 8 and Lake 

 Victoria 7 endemic species. Of 7 types in Nyasa 3 are endemic ; 

 of 5 in Lake Albert 2 are endemic. Lake Edward, lastly, 

 contains 2 forms, both of which are endemic. — In addition to 

 three genera of wider distribution, the Mutelidas contains the 

 doubtful genus Moncetia, to which reference has already been 

 made — a genus described as peculiar to Tanganyika, lluiela 

 nilotica is the only species in the family recorded from more than 

 one lake, it being found in both Albert and Edward Nyanza as 

 well as in Egypt. Each of the bigger lakes exhibits a single 

 endemic form of Miitela. The genus Pleiodon is only represented 

 by P. spekei, confined to Tanganyika — it is one of the species 

 named by Woodward from Speke's original collection. Spatha i.s 

 unrepresented in Tnng.-myika and the smaller lakes, but a series 

 of three endemic forms is known in Nyasa. — Lastly, yEtheria 

 eUiptica, sole representative of the ^theriidfe, occurs in Tangan- 

 yika and Victoria Nyanza, but has not been recorded from the 

 other lakes, although it is widely distributed in Tropical Africa. 



While a considerably smaller number of forms is involved here 

 than was the case with the Gasteropods, there is yet an indication 



Proc. Zool. Soc— 1920, No. XXXVII. 37 



