126 



BATRACHIA. 



these plates ; and some small forms are even armoured dorsally. 

 The degree of persistence of the notochord is very variable, the 

 peripheral elements being sometimes merely separate pleuro- 

 centra and hypocentra, sometimes rings or cylinders ; while 

 completed biconcave centra are rare, except in the large 

 crocodile-shaped species of the Trias. The latter were originally 



FIG. 82. 



Branchiosaurus amblystomus ; restoration of skeleton (A) and ventral armour (B) 

 by H. Credner, about nat. size. L. Permian ; Saxony. The tail is known 

 to have been much longer than the extent of the ossified caudal vertebrae. 



named Labyrinth odonts by Owen in allusion to the complex 

 structure of their teeth (fig. 90, p. 138), and are the latest 

 members of the Stegocephalian order hitherto identified with 

 certainty. They make an extremely close approximation to 

 the more generalized types of Anomodont reptiles. 



