FOSSIL REPTILES. 269 



phalanges on the little finger, which is not longer than the 

 thumb. The three others, particularly the medius, are elon- 

 gated. This arrangement produces a pointed hand, in which 

 the thumb and the index alone have the unguical phalanges 

 armed with a claw. 



The calcaneum of tortoises, in general, has no prominence 

 behind, so that the tarsus is as flat as a carpus. It is com- 

 posed of six or seven bones in the sea-tortoises. The bones of 

 the metatarsi of the great and little toe are shorter than the 

 others, and singularly broad and flatted. 



We must now speak of the fossil remains of this genus. 



The number of existing tortoises is so very considerable, 

 that it 13 very difficult to decide whether or not a fossil tor- 

 toise belong to an unknown species. It is necessary to com- 

 pare not only the carapaces, and bucklers provided with their 

 scales, but also the skeletons themselves, to observe the junc- 

 tures of the ribs and of the other bones which concur to the 

 composition of these cuirasses. The most that can be done 

 for many of them is to assign their subgenus, which, however, 

 is a point of considerable importance, as it tends to throw light 

 on the origin of the stratum which envelopes them, or at least 

 on the existence or non-existence of some dry land in the 

 neighbourhood of the waters where this stratum was formed. 



A remarkable abundance of the bones of Trionyx are found 

 in the same strata with palaeotheria, &c. though this subgenus 

 has never been known to exist in Europe at any period of 

 authentic history. There are, in fact, no species nearer to us 

 than in the Nile and the Euphrates. These are the thirst of 

 the Nile and the rafcht of the Euphrates, (^Testudo triunguis,) 

 All the other species whose country is known inhabit the rivers 

 of warm climates, which renders it probable that those whose 

 country is not known have a similar habitat. It seems pro- 

 bable that the tortoise described by Aristotle under the name 

 of emys, was the species of the Nile just mentioned. It is the 

 only species of which he could affirm that the head was suf- 



