TORTOISES AND TURTLES. 



103 



plastron of the land-tortoises are shown in Fig. 29, 

 from which it will be seen that there are six pairs of 

 symmetrical horny shields, arranged on either side of 



FIG. 29. The middle and left side of the 

 lower shell, or plastron, of a Land- 

 Tortoise. 



IG. 28. The right half of the upper 

 shell, or carapace, of a Tortoise, 

 with the horny shields removed. 

 The thick black lines show the 

 boundaries of the horny shields, 

 while the zigzag lines indicate the 

 divisions between the underlying 

 bony elements of the shell. 



the middle line of the shell. This type of plastron is 

 characteristic of nearly all the tortoises of the northern 

 hemisphere ; but in a smaller group, now confined to 



