xxiv INTRODUCTION. 



Ophidia. The Crocodilia, remains of which occur in both the Middle and Upper 

 Eocene beds, are of no special interest, the most important point being the occurrence 

 of the genus Tomistoma, a further proof of the former wider range of this genus, which 

 at the present day is represented by a single species found in the rivers of Borneo, 

 Sumatra, and Malacca. One of the species now described is interesting, as being 

 in several features intermediate between Oharialis and Tomistoma, in this respect 

 approaching the genera Thoracosaurus and Oavialoswchus, the latter of which, 

 however, is regarded by Mr. Lydekker as identical with Tomistoma. 



Among the Chelonia the Athecate group are represented only by a species of 

 PsephopJiorus, the humerus of which represents the extreme degree of modification 

 for pelagic life. This form occurs in the marine Middle Eocene beds, where it is 

 accompanied by remains of another Sea-Turtle, a member of the genus Thalassochelys. 

 The terrestrial Cryptodira, remains of which are confined to the Fluvio-marine (Upper 

 Eocene) beds, are represented by several very large species of Testudo, which approach 

 in size the giant Tortoises of Madagascar, the Mascarene and Galapagos Islands. 

 In the presence of a nuchal shield and double gulars, they approach most nearly the 

 Tortoises of Aldabra and Madagascar, and may, in fact, be the direct ancestors of 

 those species, as well, possibly, as of some of the extinct Indian forms. The 

 occurrence of numbers of the shells of such strictly terrestrial forms as these, 

 mingled with tree-trunks and bones of mammals, makes it clear that we owe these 

 richly fossiliferous deposits to floods sweeping down a great river draining a 

 land-area lying immediately to the south or south-west (see Beadnell, ' Report on 

 the Fayu m,p. 66). 



The Pleurodira are represented in both the Middle and Upper Eocene beds : two 

 genera are at present known, one [Stereogenys) especially remarkable on account of 

 the modification of the mandible and palate for crushing the food. In the mandible 

 the greatly enlarged symphysis is broad and flat; and in correlation with this a 

 secondary hard palate is formed by the meeting of the maxillse and palatines in the 

 middle line beneath the nasal passage, so that the internal nares open far back, behind 

 the level of the crushing-surface of the jaws. The other genus of Pleurodirans is 

 Podocnemis, remains of M'hich are found both in the Middle and Upper Eocene beds 

 of this region. The same genus also occurs in the Lower Eocene of England and 

 India, but at the present day is confined to Madagascar and South America. This 

 peculiar distribution suggests that although these Chelonians may in the first instance 

 have reached the Ethiopian continent from the north, probably it was thence that they 



