LAND- TOR TOISES. 



47 



The Land-Tortoises and Terrapins. 



Family Testudinid^e. 



The land-tortoises, together with the greater number of the fresh -water 

 tortoises, or terrapins, of the Northern Hemisphere, as well as their southern 

 allies, collectively constitute one of several families belonging to the first great 

 group of the order. From the circumstance that all its 

 members are so constructed as to be able to withdraw 

 their heads within the margins of the shell by a bending 

 of the neck in an S-like manner in a vertical plane, the 

 group may be conveniently designated S-necked tortoises ; 

 their scientific designation being Cryptodira. Since, how- 

 ever, the soft-tortoises likewise retract their heads in a 

 similar manner, it is obvious that this character alone will 

 not suffice to define the group, and it must accordingly be 

 supplemented by others. Although the degree of ossifi- 

 cation of the shell is very variable in the group, the 

 carapace and plastron being in some cases welded into a 

 complete box, and in other instances separate, yet there 

 is invariably a complete series of marginal bones, con- 

 nected with the ribs ; the . presence of the full series of 

 marginals, together with the S-like retraction of the neck, 

 being sufficient to distinguish the group. A peculiarity 

 in which the members of the group differ from those of 

 the next one, is to be found in the circumstance that the 

 bones of the pelvis remain throughout life unconnected 

 with the plastron ; while in the greater number of cases THB LEFT HALF 0F THB PLAS - 



• i 1 ii i . ,, • r> • TRON OF THE CHAIBASSA 



the latter, as shown in the accompanying figure, comprises terrapin. 

 only six pairs of horny shields, their being no intergular 



shield between the first pair, or gulars. The skull is characterised by the tympanic 

 ring (t in the accompanying figure) having a notch in its hinder border, and also 



by the condyle on its quadrate - bone 

 fitting into a hollow at the hinder end 

 of the lower jaw. This S-necked group 

 includes the marine turtles, and all the 

 tortoises of the Northern Hemisphere, 

 with the exception of the soft river- 

 tortoises, and thus comprises by far the 

 greater number of the living represent- 

 atives of the entire order. Although well 

 represented in Africa and South America, 

 the group is quite unknown in Australia. 

 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 



SIDE VIEW OF THE SKULL OF A LAND-TORTOISE, WITH 

 THE LOWER JAW REMOVED. 



