Geographic and Geologic Relations 429 



obliterated Oligocene, Miocene or recent remains over the 

 western part, the existence of two species of Scleropages, 

 as little modified but far-travelled descendants of an osteo- 

 glossid type, from Sumatra and Borneo to N. E. Australia, 

 links up the whole in geologic continuity. 



A second Arapaima offshoot may either have worked 

 northward as Brychaetiis by the Afro-Hispanic bridge or 

 may have crossed directly by the N. Atlantis bridge. 



The Notopteridae are remnants of a group that must 

 have had a wide distribution in geologic time, and which 

 during their evolution must have followed pretty closely, 

 the later line of travel pursued by the Osteoglossidae, to 

 which and to the Hyodontidae, rather than to the Clupe- 

 idae, we would most nearly assign them. So the rather 

 primitive and normal genus Notopterus, and the more modi- 

 fied Xenomystus, that are found from West Africa to the 

 White Nile, are represented by three species of the former 

 in India, Burmah, and Malaya, having doubtless spread 

 thither by the Afro-Indian land mass, that the Osteoglossids 

 and numerous others took advantage of. Many structural 

 characters again ally Notopterus with Osteoglossinn and 

 Arapaima. All of these facts then require for their explana- 

 tion, such past geologic connections as those already indi- 

 cated, for their proper interpretation. 



The remarkable family Mormyridae, that includes 93 

 species peculiar to central Africa, from the west coast to 

 the Nile, shows marked affinities with the Notopteridae, 

 the Osteoglossidae, the Hyodontidae, and the Albulidae. 

 They are probably descended from a type that more or less 

 combined characters of all of these. The very circum- 

 scribed area in Africa that some species or genera occupy; 

 the extreme modification in oral structure that many of 

 them show — which however is paralleled in central S. 

 America by Sternarchus and related genera of Gymnod- 

 ontidae; — their entire absence from the American conti- 

 nents; as well as the affinities above suggested; would all 

 incline one to believe that from some primitively American 

 ancestry, related to the families just treated of, descendants 

 that alone survived in the Central African area, evolved 

 actively into many as well as varied new species and genera. 



