THE TORTOISES 2403 



ribs of crocodiles; and it will thus be evident that Chelonians have no representative 

 of the breastbone, or sternum, which is so commonly present in other groups of 

 Vertebrates. 



As regards their limbs, the members of this order present a great amount of 

 variation, some of them, like the land tortoises, having the feet adapted for walking, 

 while in the turtles the entire limbs are modified into paddles for swimming. In 

 some cases, each of the five toes may be furnished with strong, curved claws, but in 

 others, like the soft tortoises, only three are thus armed. As a general rule, the 

 number of joints in the toes of the fore-limb, counting from within outward, is 2, 3, 

 3, 3 3. while in the hind-limb they are more generally 2, 3, 3, 3, 2, although in a 

 few species the number is the same as in the fore-limb. In both limbs the num- 

 ber of these joints may, however, be reduced, but, except among the soft tor- 

 toises, they are never augmented. Very generally, the surfaces of the limbs, 

 especially the anterior ones of the front pair, are protected by horny plates of vari- 

 able size, which, among the land tortoises, may be underlaid by nodules of bone. 



In habits the members of the order display as much diversity as in structure; 

 some being carnivorous and others herbivorous, while some are marine, others fresh 

 water, and others, again, more or less exclusively inhabitants of dry land. All, how- 

 ever, are fond of water, and even the most strictly terrestrial species can, we believe, 

 swim. With the exception of the turtles, the eggs are hard shelled, and these are 

 in all cases deposited on land, the turtles resorting to the shore at certain seasons 

 for this purpose. As regards distribution, tortoises are especially characteristic of 

 the warmer parts of the globe, only two species inhabiting Europe and these con- 

 fined to the more southern parts of the Continent. The various groups and families 

 are, however, by no means equally distributed over the different regions of the globe. 

 The side-necked tortoises, for instance, are now exclusively confined to the Southern 

 Hemisphere, and in Australia are the only representatives of the order; whereas 

 the S-necked group attains its greatest development in the opposite half of the 

 world, although represented in many countries lying to the south of the Equator. 

 The soft river tortoises, again, are confined to the waters of Asia, Africa, 

 and North America, being totally unknown both in South America and in Aus- 

 tralasia. Giant land tortoises within comparatively recent times have been con- 

 fined to what are known as oceanic islands, although they formerly occurred on 

 most of the large continents; while the smaller members of the same genus are far 

 more numerous in South Africa than they are in Asia. Geologically, the order is a 

 very ancient one, being represented throughout the whole of the Secondary period, 

 and thus commencing at a date when true crocodiles are not known to have come 

 into existence. 



According to our own views of their mutual relationships, the Chelonians may 

 be divided into three main groups, or suborders, which may be severally designated 

 S-necked tortoises (including the turtles), side-necked tortoises, and soft tortoises. 

 Some writers would, however, remove from the first group the so-called leathery 

 turtle, to make it the type of a group equal in value to the whole of the other three, 

 which are thus collectively brigaded under a common title. Adopting the former 

 arrangement, we commence our survey of the various members of the order with 



