48 COFE 



fication forms a superficial layer. In the Labyrintliodon- 

 tidse tiae ossification is more complete. The dentine may 

 be entire, or deeply inflected, so as to form straight or 

 labyrinthic folds. 



Subclass II.— UEODELA. 



There are three orders of Urodela : 

 a, An OS intercalare. 

 Palatine arch and vomer present; Proteida. 



aa, No OS intercalare. 



A maxillary arch and vomers; Pseudosauria. 



No maxillary arch or vomers; Trachystomata. 



Under tlie Proteida the only family known is the Pro- 

 teida (Fig. 16.) 



The Pseudosauria embraces the following families : 

 Cryptobranchidge; Amblystomidse ; Hynobiidse; Plethodon- 

 tidse; Thoriidse; Desmognathidse; Salamandridse ; Pleuro- 

 delidse; Amphiumidse; Cseciliidise. 



The Trachystomata includes only the family of the Si- 

 renidse. 



A possible member of the Proteida occurs in the Coal 

 Measures, but certainly known members of the order are 

 not found in a fossil state. Of Pseudosauria fossil forms 

 are first found in the Laramie in America, and they are not 

 uncommon in the Neocene in Europe. Trachystomata are 

 not known fossil. 



