xxn INTEODIJOTION. 



numerically, but increase greatly in size and number of transverse ridges. Dr. Chalmers 

 Mitchell has lately shown (Trans. Zool. Soc. vol. xvii. 1905, pp. 464-7) that theSirenia 

 and Proboscidea resemble one another in the arrangement of the intestinal tract and 

 that in neither group is there any trace of the Ungulate specialisation : it is also 

 significant that he states that Hyrax likewise approaches the Sirenia in this respect. 

 In a former paper (Phil. Trans, vol. 196 B (1903) p. 116) it was stated that the possession 

 of a non-deciduate zonary placenta was common to the two groups in question, but it 

 has been pointed out by Messrs. Assheton and Stevens (Quart. Journ. Micr. Sci. vol. xlix. 

 1905, p. 1) that this is an error, and that, as a matter of fact, in the Proboscidea the 

 placenta is deciduate. At the same time, these writers show that in both groups 

 the placenta, in addition to the short villi, also possesses a number of larger and longer 

 villi, which deeply penetrate the maternal tissue and seem to be torn off at parturition. 

 Although these points of similarity, taken separately, may be of no great value, 

 together they supply a very strong argument in favour of the close relationship of the 

 two orders. 



All the Carnivora at present known from the Upper Eocene of the Fayum belong 

 to one family, the Hysenodontidse, of the primitive group, the Creodonta. They are 

 remarkable from the fact that in the four genera represented, viz. Sinopa, Apterodon, 

 Pterodon, and Hyoenodon, the molar teeth show four stages in the development of the 

 cutting-blade and in the reduction of the talon and the postero-internal cusp. It 

 seems highly probable that these animals entered Africa from the north, where 

 Creodonts are found in the earlier Eocene deposits ; but at the same time the fact that 

 the Zeuglodont Protocetus from near the bottom of the Lower Mokattam beds, has a 

 dentition which is practically that of a Creodont, clearly indicates its origin from 

 members of that group, which may therefore have inhabited this region at a still 

 earlier period. Since, however, Protocetus is already fully adapted for marine life, 

 this is by no means certain, for it may have crossed from the northern side of the 

 Nummulitic sea. Another argument for the existence of earlier Creodonts in 

 the Egyptian region is that, since there is considerable probability that Africa was 

 connected by a land-bridge with South America in late Cretaceous and possibly even 

 at the beginning of the Tertiary period, their presence in Africa would account for 

 the existence of the Sparassodonta in the Tertiaries of Patagonia. 



The Zeuglodonts of the Fayum, taken together with a species, Protocetus atavus, 

 recently described by Prof. E. Fraas (29) from the limestones of the Mokattam Hills, 

 form a series showing a complete transition, so far at least as the dentition is concerned. 



