eigenmann: fresh water fishes. 295 



without mammals and especially placental mammals, during the Eocene. 

 When, toward the close of the Eocene this land-bridge was submerged, 

 there already existed many types that have been conserved until our 

 time. * * * Archamazonia, after the loss of the connection with Africa, 

 consisted of Archiguyana and Archibrazil. * * * While the distribution 

 of the existing types of mammals is a result of changes in geography 

 during Tertiary time, the most fundamental facts in the distribution of the 

 fresh-water fauna dates from the Mesozoic epoch. The fresh-water fauna 

 of Chili preserved such a remnant of the Cretaceous fauna almost intact, 

 and even the connection between the two Americas has not at all modi- 

 fied the South American fresh-water fauna. * * * There is a further dif- 

 ference in the distribution of mammals and fresh-water mussels. The 

 former migrate on land-bridges in most directions, the fresh-water fauna 

 generally in only one, due to the opportunity given by the currents. 

 Thus although there was an invasion of Cyprinid fishes into Africa there 

 was no corresponding emigration of yEthiopian types. * * * 



"The fresh-water fauna is not only older but also much more conserva- 

 tive than the distribution of mammals. One of the most striking examples 

 of this is given by the history of Africa. While the characteristic mam- 

 mals are Neogene immigrants, and Lydekker proceeds quite correctly in 

 making Africa an annex only of the Holarctic region, thus establishing 

 his Arctogaea, with relation to the fresh-water fauna, Africa is a part of 

 South America, somewhat modified by the Neogene invasion of Cyprinid 

 fishes. If as regards mammals Africa belongs to Arctogaea, with relation 

 to the fresh-water fauna it belongs to the Archhelenic region." 



It is seen from the above that von Ihering divides South America into 

 two distinct faunal areas, that he attributes the division to an ancient sep- 

 aration of the continent into Archiplata and Archamazonia, that he places 

 the separating sea north of Uruguay and that he divides Archhelenis into 

 Archiguyana and Archibrazil by the eastern Amazon valley. Derby has 

 objected to the Uruguayan sea because there is no geological evidence 

 for it. The fresh-water fishes demand a more southern line on the east 

 than northern Uruguay, and, considering the fresh-water fishes only, there 

 is no hesitation in placing the line in the La Plata-Paraguay valley and 

 allowing it to extend to the north-west corner of Archiplata, wherever that 

 may have been, probably in central Peru. 



