The Tanganyika Problem Reviewed 473 



A large part of the Niger, South Soudan, and central 

 African region seems to have been of no great elevation, 

 though what is now the Congo drainage area may have 

 been considerably higher on till Miocene time. The united 

 eastern American and Niger rivers may gradually have 

 joined over this S. Atlantis basin, and discharged south- 

 wardly into a South Atlantic sea. Such would again ex- 

 plain how various primitively freshwater teleosts sent out- 

 lying members into brakish and ultimately marine surround- 

 ings of southern waters, from which they could spread 

 widely during succeeding periods of time. 



Across the connecting land a few representatives of 

 silurid, characinid, cyprinodont and cichlid families, with 

 others of lesser subsequent importance, must have passed, 

 their migration being doubtless greatly helped during 

 periods of marsh-land flooding. That the migration was 

 not wholly eastward from America to Africa however, but 

 that a westward invasion also took place, is suggested by 

 the probable relation of the African Protopterus to the 

 American Lepidosiren. For owing to the more primitive 

 structure of Protopterus, as compared with the closely 

 allied Lepidosiren, Kerr, Boulenger and other authors have 

 considered it probable that modified derivatives of Protop- 

 terus crossed the connecting land-area — possibly in early 

 Eocene times — and gave rise to the American genus. At 

 the time of the early Eocene then, Africa and S. America 

 were simultaneously being stocked with evolving members 

 of the above four families, though on the whole conditions 

 seem to have been more helpful in America for their multi- 

 plication from that time to the present. For while S. 

 America now has about 300 species of silurids, Africa has 

 150; while the characinids number 659 species in the form- 

 er area, there are about 100 in the latter; while the cyprino- 

 donts number about 160 species in S. America, there are 42 

 in Africa. The cichlids alone seem to have found a more 

 congenial home, or special environal factors that hastened 

 specific variation in Africa over America. For while the 

 latter contains about 190 species, there are close on 220 

 in the former. 



