Decembbb 7, 1900.] 



SCIENCE. 



863 



I may uote here one more fact referring 

 to the fresh water fauna : the dispersion of 

 the cyprinoid fishes. These Holarctic fishes 

 did not reach Australia, already isolated 

 by the sea, but invaded Africa and Mad- 

 agascar. Lemuria must therefore have per- 

 sisted in connection with Asia, when the 

 Australian region was already isolated. 

 Thus Africa offers the same mixture of an- 

 cient indigenous elements and l^eogene im- 

 migrants as Argentina and Southern Brazil, 

 on account of the intrusion of archamazonic 

 immigrants. Had this invasion occurred in 

 the Eocene period, the Cyprinidse would 

 have reached Brazil ; supposing it to be Pli- 

 ocene, these fishes would not have reached 

 Madagascar. Probably Africa received its 

 placental mammals at the same time that 

 the invasion of Cyprinidse into Africa took 

 place, one of the most remarkable events in 

 zoogeography. 



We have no knowledge at all of the Cre- 

 taceous and Eocene mammals of Brazil, 

 Guyana, Africa and Australia ; it is im- 

 possible to give a complete historj' of the 

 mammals with incomplete materials. But 

 combination of the known facts makes it 

 probable that during the Cretaceous and 

 Eocene period Archhelenis, or Stenogsea, 

 was without placental mammals and that 

 their origin was in Eurygsea. In regard 

 to the flora the same holds good for many 

 families of wide distribution, as for example 

 the Cupuliferse. 



With reference to the terms used by 

 Blandford, Lydekker and the writer, it 

 must be said that the intention of the first 

 two was to give names to existing zoogeo- 

 graphical regions, while the terms intro- 

 duced by me refer to supposed, ancient zoo- 

 geographical and geographical regions. The 

 two great Cretaceous continents Eurygsea 

 and Stenogsea may have existed also during 

 a part of the Eocene period and then dis- 

 membered. From Stenogsea, or Archhelenis, 

 were separated first Bengal and then Mada- 



gascar, while Archamazonia after the loss 

 of the connection with Africa consisted of 

 Archiguyana and Archibrazil. Eurygsea 

 split into (1) Archiboreas corresponding to 

 the actual holarctic region and (2) Archi- 

 notis from which, in the Eocene, Archiplata 

 was separated. 



The comparison of the distribution of the 

 mammals with the fresh water fauna makes 

 especially evident the differences in the geo- 

 graphical conditions which must have de- 

 termined their distribution. While the dis- 

 tribution 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 rem- 

 nant of the Cretaceous fauna almost intact, 

 and even the connection between the two 

 Americas has not at all modified the South 

 American fresh-water fauna. On the other 

 hand, representatives of the Archamazon- 

 ian fauna, in correlation with the geo- 

 graphical modifications of Central America 

 and the Antilles have invaded the southern 

 parts of the nearctic region. Thus in the 

 Rio Usumacinta of Mexicao beside Cyprini- 

 dse and Chromidse we find also CharacinidsB 

 and Lepidosteus, also species of Glaharis in- 

 termediate between the northern Unios and 

 Anodontas. There is a further diiference 

 in the distribution of mammals and fresh- 

 water mussels. The former migrate on 

 land bridges in both 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 ^Ethiopian types. A similar 

 fact is the sudden appearance of the Ethi- 

 opian faunal elements in the valley of the 

 Nile, which occurred only at the close of 

 the Pleistocene, as proved by paleontolog- 

 ical facts. While the Pliocene connection 

 of the two Americas was sufficient to mod- 



