14 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



The characters displayed by the three divisions in question indicate 

 their relationship to be as follows: The orders of Division I iDresent in 

 their cranial structure a greater resemblance to the limb-finned or 

 crossopterygian fishes than do either of the others. The third division 

 is the most divergent from the type, and is in various respects the most 

 specialized. This specialization consists' not only in a departure from 

 the primitive Batrachia, but also from all other forms of vertebrata. 

 Its specialization is seen in the loss and coossiflcation of various parts 

 of the skeleton. The Urodela display characters intermediate between 

 the extremes of the class. jSTear them the Trachystomata (Sirenidae) are 

 still more inferior by loss of parts of the skull and of the pelvic arch. 

 The Proteida have lost the maxillary arch of the Stegocephali, but re- 

 tain their os intercalare. 



PHYLOGENY. 



The class Batrachia holds an important position in the history of the 

 vertebrata, as the first member of that kingdom which occupied the 

 land on the advent of the conditions suitable for air-breathing types. 

 It thus stands in ancestral relation to the lines of the Sauropsida and 

 Mammalia, and as the immediate descendants of the fishes. As regards 

 the extinct orders, the primitive type is evidently the Ganocephala, 

 whose vertebral column displays an arrest of characters which are 

 transitional in the higher vertebrata. From this group the orders 

 Rhachitomi, Embolomeri,and Stegocephali have been evidently derived. 

 We may then present the following genealogical table of the class 

 Batrachia : 



Salientia. 



\ Trachystomata. 



\ / 



\ / 



\Urodela. 



\ \ 



\ \ 



\ Proteida. 



Embolomeri. Stegocephali. 



\ / 



Rhac 



litomi. 



Gano 



cephala. 



