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 harcl-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 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 
