X\IV 
I\TI{()1)UCT10X. 
Opliidia. 'riie Ci'ocodilia, remains of wliicli occur in both the Middle and Upper 
I'iocene beds, are of no s])ecial interest, the most important point being the occurrence 
of the genus Toniistoma, a furtlier proof of tlje former wider range of this genus, winch 
at the ])rcsent day is re])resented 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 Gliarialis and Toniistoma, in this respect 
ap])roaching tlie genera Thoracosanrus and Gavialosuchus, the latter of which, 
however, is regarded by Mr. Lydekker as identical with Toniistoma. 
Among the Chelonia the Athecate group are represented only by a species of 
Psephoptiorns, 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 
accom])anied by remains of another Sea-Turtle, a member of the genus Thalassochclps. 
The terrestrial Cryptodira, remains of wliich are confined to the Fluvio-mariue (Upper 
Eocene) beds, are represented by several very large species of Testudo, which aj^proach 
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, ‘ Iveport on 
the Fa}!! m.p. GG). 
The Pleurodira are represented in both the Middle and Upper Eocene beds : two 
genera are at ]!resent known, one [Stereogenys) especially remarkable on account of 
the modification of the mandible and palate for crushing the food. In the mandible 
tlie greatly enlarged symphysis is broad and flat ; and in correlation with this a 
secondary hard palate is formed by the meeting of the maxilhe 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 which are found both in the Middle and Upper Piocene beds 
of this region. The same genus also occurs in the Lower Plocene 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 
