144 &Et> TILES AND BIRDS. 



are placed within the thorax, and articulated to the sides of the 

 vertebral column. 



Of the vertebral column in these extraordinary animals, Sir 

 Richard Owen remarks that the manifold modifications of the frame- 

 work which render it a portable abode, appear to have been given as 

 a compensation for inferior powers of locomotion, and the absence 

 of offensive weapons. But with all its modifications, the same 

 number of pieces are found in the bony skeleton as in other ordinary 

 vertebrates, the form and volume of many of these pieces being 

 alone changed. 



The skin which covers the body of these animals sometimes pre- 

 serves its softness, being altogether devoid of scales ; but in nearly 

 all the species it is covered with horny scales of great consistency. 

 Upon the plastron and carapace these scales form large plates, the 

 arrangements and appearances of which vary in different species, 

 some of them being often remarkably beautiful. The material 

 which bears the name of tortoise-shell forms an important article 

 of commerce. 



Aristotle mentions three groups of Tortoises namely, Land 

 Tortoises, Sea Tortoises, and Fresh-water Tortoises. Cuvier divides 

 them into five sub-genera: i, Land Tortoises, Testudo ; 2, Fresh- 

 water Tortoises, Emydes ; 3, Marine Tortoises ; 4, Chelydes, Testudo 

 fimbriata ; 5, Soft Tortoises, Trionyx in which he was followed by 

 Dr. Gray in the British Museum Catalogue, who made them the 

 third order of Reptiles in his arrangement, as follows : 



I. TESTUDINID^E. 

 Testudo, Chersina, Kynixys, Pyxis. 



II. EMYDID/E. 



Geoemyda, Emys, Cyclemys, Malaclemys, Cistudo, Kinosternon, 

 Chelydra, Platysternon. 



III. CHELYDID^;. 



Sternotherus, Pelomedusa, Hydraspis, Chelymys, Phrynops, Chelodina, 

 Hydromedusa, Chelys, Peltocephalus, Padocneinis. 



IV. TRIONYCID^. 

 Trionyx, Emyda. 



V. CHELONIAD^E. 

 Sphargis, Chelonia, Caretta, Caouana 



