2902.] AND ANCIENT GEOGBAPHY. 367 



Amazonas. But we have no evidence for this, the Geology of the 

 respective countries being too incompletely known. 



9. THE RELATIONS OF AFRICA TO THE REST OF THE WORLD. 



We have seen (p. 303) that for the two main divisions of the 

 range of the Potamonince. in the Old World Egypt and the Nile 

 valley form an actual connection ; but examining this more closely 

 we find that this subfamily cannot have migrated along this route 

 from Africa to India (or vice versa), but entered Egypt from two 

 opposite directions, from the south ( Central Africa) and the north 

 (resp. northeast) over Persia, Mesopotamia and Syria. 



The causes why this way was not open in former times have been 

 briefly mentioned above (p. 333), and we shall here try to investi- 

 gate the relations of Africa and Asia with respect chiefly to this 

 northern connection. For this purpose we are to discuss also the 

 northern boundaries of Africa with reference to Europe. This is 

 the more important, since we have to consider the alleged fact that 

 fossil forms of the Potamonince have been found in Miocene fresh- 

 water deposits of Oeningen (Switzerland), Sigmaringen (Southern 

 Germany) and Northern Italy. 1 



Very important for a study of these questions is the former exist- 

 ence of a Central Mediterranean Sea, as Neumayr calls it (1890, pp. 

 332, 2,33, an d m a P P 336), or the Tethys of Suess (1894). This 

 ancient sea goes back to Paleozoic times and covered in Mesozoic 

 times the whole of Middle and Southern Europe, the present Medi- 

 terranean Sea, Northern Africa and extended eastward over Asia 

 Minor, Syria, the Caucasus Mountains and Mesopotamia as far as 

 Northern India. In the east a large bay extended southward along 

 the East African coast, which separated the Indo-Madagassian 

 peninsula (Lemuria) from Africa. In a westerly direction the 

 Tethys was broadly connected with the Atlantic Ocean, leaving 

 only the island of Spain (Meseta) uncovered. 



In these general outlines the Tethys existed in Jurassic as well as 

 in Cretaceous times, thus completely circumscribing the African 

 continent toward the north and northeast. Europe did not then 

 exist at all as a continental mass and Africa was separated from the 

 Sinic continent by an eastern continuation of the Tethys, the 



1 Thelphusa speciosa Mey. and Th. quenstedti Zitt., see Zittel, Handbuch d. 

 PalaontoL, Vol. 2, 1885, p. 714. These forms have a remote resemblance to the 

 subgenus Potamonautes, if they belong here at all. 



