298 RECENTLY DISCOVERED TERTIARY VERTEBRATA OF EGYPT. 



certain that in Northern Africa we shall have a succession of mam- 

 malian 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 verte- 

 brata, more especially the mammals, at present known from the 

 Fayum, may now be given. In the first place, it should be noted that 

 m addition to early forms of groups already known several entirely 

 peculiar types of mammalian life have been found. Amongst these 

 the most important are Arsmoiiherium, which has been regarded as 

 representing a new order of mammalia, most nearly allied to the 

 Hyracoidea, and Barytherium^ which not improbably may also repre- 

 sent a new subordinal group, but of which the affinities are at present 

 quite uncertain. 



Arsinoithe7'iimi is one of those extremely peculiar types which, as 

 in so many other instances, shows by its extreme specialization in 

 certain directions that loss of adaptability to new conditions of life 

 which almost inevitably leads to extinction. Many similar instances 

 might be quoted, one of the most notable being the Titanotheriidse 

 of North America. In its general appearance Arsinoitheriu-m 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, both pairs, unlike the horns of Rhinoceros^ being formed by 

 bony outgrowths of the skull that were probably covered with a 

 horny sheath during life. The posterior surface of the skull slopes 

 forward, and is deeply hollowed for the attachment of the powerful 

 muscles necessary to support the heavy head. The front of the snout 

 is narrow and pointed, a circumstance which, coupled with the char- 

 acter of the incisor teeth, makes it at least probable that the animal 

 did not graze, but browsed on bushes and low herbage, most likely 

 with the assistance of a mobile upper lip, like the black rhinoceros 

 of to-day. The teeth were of very peculiar structure. The dentition 

 is complete, and forms on either side of the jaw a closed series, the 

 crowns of all the teeth wearing to a common level, with the exception 

 of the anterior upper incisors which form slight hook-like jDrojections, 

 and no doubt helped in seizing the food. All the teeth are high- 

 crowned, the molars especially so, and it is further remarkable that 

 the upper molars differ entirely from the premolars in form. The 

 type of molar structure here found is quite unknown elsewhere, but 

 it may have been derived from the deepening of the crowns of molars 

 like those of Hyrax^ though some writers are inclined to regard it as 

 a specialization of the type found in Coryphodon and other primitive 

 Amblypoda. 



The limbs were short and massive, and the feet were much like 

 those of the elephant, all five toes being retained. At the same time 



