THE LAND TORTOISES AND TERRAPINS 2405 



The land tortoises and terrapins of the family Testudinidce have the shell well 

 developed and of a more or less ovoid shape; the plastron being connected with the 

 carapace either by a straight articulation or by means of sutures, while it never has 

 an intergular shield in front. The limbs are adapted more or less completely for 

 walking, and are never modified into paddles, while the head is capable of complete 

 retraction within the margins of the shell. A very important structural feature in 

 the shell is that the nuchal, or unpaired median bone in the front of the carapace, 

 does not send back processes underlying the marginal bones of the same; while in 

 the tail each vertebra has a cup in front of its body or lower portion, and a ball 

 behind. None of the members of the family are marine, but while some are 

 inhabitants of the land, others are more or less exclusively dwellers in fresh water. 

 There are, moreover, equally important differences in regard to their food, all the 

 land forms being herbivorous, while of those frequenting the water some subsist on 

 vegetable, and others on animal substances. 



By far the most numerously represented genus of the whole family 



is the one including the true or land tortoises, of which there are 

 Tortoises 



rather more than forty existing species (counting a few that have been 



exterminated within the historic period) . These tortoises, of which a few are more 

 or less aquatic in their habits, have the upper and lower portions of the shell com- 

 pletely welded together, the former being frequently very convex and much vaulted, 

 while the top of the head is covered with large horny shields. The limbs, which 

 are entirely adapted for walking, are of a club-like form, and are covered with large 

 horny scales or tubercles; their toes being tmwebbed and furnished with strong, 

 claw-like nails. The tail is always short, its proportionate length not being greater 

 in the young than in the adult. More important characteristics are, however, 

 furnished by the bony shell and skull, to observe the former of which it is of course 

 necessary that the horny shields should be stripped off. In a shell thus treated it 

 will be seen that the unpaired median neural bones of the carapace are relatively- 

 short and wide, and so arranged that a four-sided one is interposed between two 

 that are octagonal, although in some cases they are mostly hexagonal; while the 

 costal or lateral plates are alternately narrow above and broad below. Moreover, 

 the line dividing the costal horny shields from the marginals usually corresponds 

 with the suture between the corresponding bones of the carapace, whereas in the 

 other members of the family one is above the other; while a further peculiarity of 

 most species of the genus is that there is but a single caudal horny plate at the 

 hinder end of the carapace. In the skull the palate is provided with one or two 

 ridges on each side, while the hinder aperture of the nostrils is situated on the line 

 of the eyes. It may be mentioned here that, as in the majority of the representa- 

 tives of the order, the form of the shell differs considerably in the two sexes, the 

 male having the central region of the plastron deeply concave, while in the females 

 it is flat or slightly convex. 



True tortoises are distributed over Southern Europe and Asia, the whole of 

 Africa, the southern portions of North America, and South America (inclusive 

 of the Galapagos islands). They are strictly herbivorous in their diet; and certain 

 species now confined to oceanic islands, attain gigantic dimensions, and are by far 



