46 TORTOISES AND TURTLES. 



no representative of the breast-bone, 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 outwards, 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 

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

 tortoises, 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 

 variable 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, however, 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 confined 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 Australasia. Giant land-tortoises within comparatively 

 recent times have been confined 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 w^hole 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 



