The Soft-finned Teleostei 363 



of N. Africa are at home in brine pools, certain of which 

 even may be of relatively high temperature. 



While numerous genera and species however occur over 

 the area above indicated, none are met with in intervening 

 seas and estuaries, aside from the three migrants just noted. 

 But if we consider the group to have already developed 

 in earliest Eocene times, while S. America was joined by 

 S. Atlantis to Africa, and it again connected by a slight 

 bridge with S. Europe on the north and with S. W. Asia 

 in eastward extension, a complete understanding of the 

 problem is got. On the other hand endless difficulties arise 

 in attempting to explain their origin from marine ancestors. 

 For of such we have no trace. But had such once existed, 

 some common impulse, such as we practically never notice 

 in true marine species, must have caused them to press in- 

 ward and upward along rivers, so as ultimately to reach, 

 as in the case of Orestias and others, the waters of Lake 

 Titicaca at 13,000 ft. elevation. We have already satis- 

 factorily explained the origin of the striking fish fauna of 

 this lake, without needing to resort to marine sources. 



Further, why do a few venture seaward in rare cases, 

 but none become ocean dwellers? In face of these and 

 many other related difficulties, we are compelled to accept 

 an ancestral freshwater environment, alike for the whole 

 family and its predecessors. That no trace of them occurs 

 in the Australasian area, suggests that their main evolution 

 proceeded after Sino-Malaya had been separated from 

 Australasia in the later Oligo-Miocene period. 



The family that has been designated the Scombresoci- 

 dae next deserves mention. For its structural peculiarities 

 ally it with the Cyprinodonts. But the entire group is now 

 marine environally, and more or less highly modified in 

 structure. It first appears in the Upper Eocene, and so time 

 was given for possible derivation of the group from a more 

 primitive freshwater early Eocene stock. 



Resulting as two restricted side-lines and modifications 

 from the Cyprinodontidae, as did the Dalliidae from the 

 Esocidae, are the small freshwater families Amblyopsidae 

 and Percopsidae. 



