XX IXTRODUCTION. 



fauna, although there is much to be said for the opposite view. The Anthracotheriidse 

 are represented in the almost contemporary deposits of Egerkingen by the genera 

 Ancodon and Ehagatherium, just as in the Fayum, aijd, moreover, in both places they 

 are accompanied by Creodonts belonging to the Hysenodontidse ; but while the 

 Creodonts occur in the earlier beds of Europe, this does not seem to be the case with 

 the Anthracotheres, so that here there may be a trace of an interchange of forms 

 possibly towards the end of the Middle Eocene, the Creodonts having passed into 

 Africa at the same time as the Anthracotheres migrated north. Professor Osborn 

 has already suggested that such a migration took place about this time, in order to 

 account for the appearance in the Upper Eocene of Europe of forms like certain 

 highly specialised Ruminants, the Anomalures, and perhaps some Edentates. The 

 Anthracotheres persisted in Africa at least till the Lower Miocene, at which horizon 

 they are represented by Brachyodus africanus, and it is pointed out below that these 

 animals in many points, e.g. in the pelvis (see p. 185), approach very nearly 

 to the Hippopotamidse, which are probably derived from them. Remains of one 

 of the earliest and most primitive Hippopotami known, viz. H. hipponensis, hnve 

 already been found in the Middle Pliocene of Egypt, so that there is every prospect 

 that annectant forms between Hippopotamus and the Anthracotheres may be discovered 

 in this region in deposits between the Lower Miocene and the Pliocene. 



The peculiar genus GenioJiyus is perhaps the earliest-known member of the 

 Suidse, but although the lower cheek-teeth seem to be undoubtedly those of 

 a primitive Pig, the great enlargement of the anterior pair of incisors and the 

 reduction of the posterior incisors and canines are quite different from what is usually 

 found in members of this family. Geniohyus, in fact, may be regarded as an early 

 specialised form of a group of which the generalised members have still to be found ; 

 they probably inhabited Africa and passed north, perhaps in the Middle Eocene 

 migration referred to above. The occurrence of the peculiar ventral process arising 

 from the symphysial region of the mandible suggests some possible relationship with 

 the Elotheriidse of the Miocene of Europe and America, a group in which somewhat 

 similar processes occur ; but, if only on account of the peculiarities of its anterior teeth, 

 it seems impossible that Geniohyus can at most be more than an early offshoot of the 

 ancestral stock of that group. 



In the Fayum the Sirenia are represented by one genus, JEosiren, only, but in the 

 earlier and more exclusively marine beds of the Mokattam Hills, near Cairo, other 

 more primitive types occur, the skull of one of which, jEotheriiim, is described below 



