480 Evolution and Distribution of Fishes 



glossidae, that is represented by Heterotis from the Sene- 

 gal-Gambia to the Nile. This in turn connects with Osteo- 

 glossum and Arapatma in S. America, and with the more 

 primitive Dapedoglossum of N. America. The eastward 

 extension as Scleropages into the E. Indies and Australia, 

 has already been noted (p. 354). 



The puzzling family Mastacembelidae must have en- 

 tered, or evolved in, Africa, not later than early Eocene 

 time. It now includes some 38 or 40 species, at least 7 of 

 which are peculiar to Tanganyika, and 24 are tropical 

 African. The remainder extend from the Nile through 

 Syria and Mesopotamia to the East Indies. The entire 

 family is as typically freshwater as any of those studied 

 in this chapter, but its derivation is puzzling. It seems to 

 combine characters of the Notopteridae and the Mor- 

 myridae, specially of Gymnarchus in the latter family. But 

 other characters are markedly divergent, and seem to ally 

 it with the acanthopterous family Blenniidae, near which 

 it is usually placed. 



In condensed review then of this chapter, it is suggested 

 that toward mid or late Cretaceous time the Brazilian and 

 Guiana areas of S. America, that collectively have been 

 called Archenchelis, formed a rather elevated table-land, 

 over which there already existed, or there were evolving, 

 not merely a varied invertebrate fauna, but more im- 

 portantly a fish fauna in which four families — the Siluridae, 

 the Characinidae, the Cyprinodontidae and the Cichlidae — 

 were becoming dominant, alongside others. Through earth- 

 shrinkage and volcanic upheaval a large part of the central 

 Atlantis region became considerably elevated as a south 

 Atlantis bridge, that at least for a time connected Brazil- 

 Guiana with West Africa. Into and across this were 

 probably continued the large Brazilian rivers, and at least 

 the Niger, possibly also other West African rivers like 

 the Komoe and Volta. The entire area, traversed by the 

 lower reaches of these, seems to have consisted of lakes, 

 marshlands and streams, that were subject then — as a large 

 part of central Africa is still — to alternating periods of 

 flood expansion and of drying. 



