226 VERTEBBATA : KEPTILIA OR REPTILES. 



FIG. 259. 



Chameleon. 



peculiar name from their form, and from the fact that the 

 vertebrae of the tail are so slightly adherent that the tail 

 is easily broken. And lastly, there are other lacertians, 

 like the Slow-worms of Europe, and the Double-walkers 

 of South America the latter of which can move forwards 

 or backwards with equal facility that are so unlike the 

 typical lizards that naturalists hesitate whether or not they 

 ought to be retained in the order. 



Geologists recognize certain fossil lacertians as among 

 the earliest of true reptiles, and they describe them under 

 the name of Thecodants (from the Greek theke, a sheath, 

 odous, a tooth), etc. These reptiles have small scales and 

 biconcave vertebrae similar fo those of fishes, bnt they 

 are allied to the Crocodilians in having their teeth in 

 sockets. They made their appearance in the Carbonifer- 

 ous period. 



SUB-SECTION VI. 

 THE ORDER OF ENALIOSAURIA OR SEA-SAURIASTS. 



UNDER this head we may include a host of huge 

 extinct saurians which inhabited the seas and estuaries in 

 the old Jurassic and Cretaceous times, and whose struc- 



