EGYPTIAN TERTIARY VERTEBRATA 677 



in the molar teeth is increased to four in the two anterior 

 ones. In the Pliocene the mandibular symphysis becomes 

 still more shortened up ; but in some species of Mastodon the 

 lower incisors still persist, though of small size and usually soon 

 shed. The number of transverse ridges in the molars increase and 

 become deeper, till in Stcgodon (from the Pliocene of the Siwalik 

 Hills) the anterior molars may have six or seven ridges, the 

 last one eight or nine. The valleys in these teeth are deepened, 

 and may be more or less filled with cement. At the same 

 time the milk molars are displaced by the development of the 

 molars behind them, before they can be replaced from below 

 by the premolars. In Elephas proper the elongated mandibular 

 symphysis of the early forms is represented by a small process 

 forming the chin of the mandible, and never bearing any trace 

 of lower incisors. The molars acquire a much greater number 

 of transverse ridges, and become higher in the crown. In 

 Elephas primigenius there may be as many as twenty-seven 

 ridges in the last molar. All this long series of changes is 

 illustrated by specimens shown in the Palaeontological Galleries 

 of the Natural History Museum, and representing perhaps the 

 most complete history of any Mammalian group yet known. 



In the Upper Eocene beds the Hyracoidea are represented 

 by two genera, Megalohyrax and Saghatherium, including several 

 species. None of these throw any light on the relationships 

 of the order ; but some of them are of large size, and indicate 

 that formerly the group was of far greater importance than 

 it is to-day, when its only representatives are a few compara- 

 tively small species, all of which (according to some authorities) 

 should be placed in a single genus, Procavia (Hyrax). 



The occurrence of remains of Sirenians in the Middle Eocene 

 beds of Egypt has long been known, Owen having described 

 — under the name Eotherium — a brain cast of one of these 

 animals from the Mokattam Hills near Cairo, so long ago as 

 1875, and further remains from the same locality were noticed 

 by Filhol in 1878. Within the last four or five years not only 

 have skulls and other portions of Eotherium been found, but 

 remains of other genera have come to light, both from the 

 Mokattam Hills and from the somewhat later deposits of the 

 Fayum. These early forms have been described by Dr. O. Abel 

 and the present writer. Their chief points of interest are those 

 in which they show approximation to the land-mammals from 



