EGYPTIAN TERTIARY VERTEBRATA 671 



uncertain. It is, however, from the Upper Eocene fluviatile 

 beds that by far the greater number of forms have been ob- 

 tained. These beds are obviously the deposits of a great 

 river, probably flowing from the south-west, and carrying 

 down in its floods the carcasses of drowned animals inhabiting 

 its banks, together with vast numbers of tree-trunks which 

 to-day, in a silicified state, are strewn over the plains formed 

 by the dip slopes of these beds. This series of fluviatile beds 

 seems to have continued with some interruptions throughout 

 the Oligocene and Miocene periods, continuing, probably, till 

 well on in the Pliocene ; and it is in such deposits at Mogara 

 and the Wadi Natrun that the Miocene and Pliocene faunas 

 above referred to are derived. In fact, the conditions seem so 

 favourable to the preservation of vertebrate remains, that it is 

 almost certain that only further exploration of the region to 

 the north of the Fayum depression is necessary to lead to the 

 discovery of faunas at other horizons. If this should prove to 

 be the case, then it seems certain that in Northern Africa we 

 shall have a succession of mammalian types second in interest 

 only to the wonderful series found in North America. 



A brief account of some of the more important of the fossil 

 Vertebrata, more especially the mammals, at present known 

 from the Fayum, may now be given. In the first place it 

 should be noted that, in addition to early forms of groups 

 already known, several entirely peculiar types of mammalian 

 life have been found. Amongst these the most important are 

 Arsinoitherium, which has been regarded as representing a new 

 order of mammalia, most nearly allied to the Hyracoidea, and 

 Barythcriitm, which not improbably may also represent a new 

 sub-ordinal group, but of which the affinities are at present 

 quite uncertain. 



Arsinoitherium is one of those extremely peculiar types 

 which, as in so many other instances, shows by its extreme 

 specialisation in certain directions that loss of adaptability to 

 new conditions of life which almost inevitably leads to ex- 

 tinction. Many similar instances might be quoted, one of the 

 most notable being the Titanotheriidae of North America. In 

 its general appearance Arsinoitherium must have much resembled 

 a large rhinoceros, but instead of having one or two horns in 

 the median line, it not only possessed a pair of small horns 

 situated over the orbits, but also a pair of enormous nasal horns, 



