206 



REPORT OF NATIONAL MUSEUM, 1898. 



VI. The Older of degeueracj' of the elements of the scapular arch is 

 (l)limb; (2) iiiterclavicle (generally); (3) costal attachment; (4) sternum. 



VII. The order of disappearance of parts in the pelvis is (1) pubis 

 and ischium together (generally; see Ampliishcena) ; (2) limb; (3) ilium. 



The conclusion that the rudimental condition of the arches and limbs 

 is due to degeneracy is supported by paleontologic evidence, which 

 shows that the ancestral orders of the Rej)tilia (Cotylosauria and 

 Theromora) had well-developed limbs. Similar evidence shows that the 

 Sauria and Ophidia had a common ancestor; but, as already remarked, 

 whether that ancestor was a Theromor or a Ehynchocephal remains 

 uncertain. 



Within the limits of the Sauria the series of affinities expresses in 

 some degree the phylogenetic succession. We can express these in a 

 tabular form as follows : 



Rhiptoglossa Nyctisaura Thecoglossa Leptoglossa Annul ATA 



Pachyglossa 



This phylogeny presupposes that the superfamilies in which the 

 petrous bone extends in advance of the anterior semicircular canal are 

 of later origin, or were derived from those, in which this is not the case. 

 It must be borne in mind, however, that this difference is of very ancient 

 origin, since in the Permian epoch the Cotylosauria have the petrous 

 bone developed forward, and the Pelycosauria have it much abbre- 

 viated. The Pythonomorpha of the Cretaceous also have the abbre- 

 viated petrosal in strong contrast to the existing Thecoglossa, where 

 it is produced. Nevertheless the Pachyglossa display such affinities in 

 many directions that they are probably ancestral to the other super- 

 families. The dentition of the Agamida^ is quite identical with that 

 of many of the Rhynchocephalia, and with that of the Chameleons 

 as well. It is a modification of the primitive rhizodont dentition which 

 prevailed during the Permian. The pleurodont dentition is another 

 modification which points to the Iguanid:e as the starting point of the 

 families which also possess that type of dentition. 



The intermediary position of the Diploglossa between the thick and 

 thin tongued lizards 1 pointed out in 1804, and its tendencies toward 

 the Nyctisaura also are unmistakably seen in Xenosanrus. The Nycti- 

 saura have degenerated in the characters of their vertebra?, for I do 

 not believe this character to be of primitive origin, or to indicate that 

 the superfamily is related to the Permian Pelycosauria, which have 

 similar vertebrte. 



