180 REPORT OF NATIONAL MUSEUM, 1898. 



masked iu some genera of Pythonomorj)ha by the extension of the 

 exoccipital over the paroccipital as a thin lamina on the posterior side; 

 but its true relation to the petrosal can be seen on the anterior side. 

 There can be no doubt that the Pythonomori)ha form a line distinct 

 from the Sauria, and that their resemblances to the Varani are the 

 result of a parallel evolution rather than an indication of near affinity, 

 as supposed by Cuvier. 



The failure of Cuvier, Owen, Dollo, Baur, and Marsh to perceive this 

 fact is due to their want of information as to what the differences 

 between the Ophldia and Sauria really are. Bouleuger only has 

 reached correct views on the subject, although not on account of the 

 structure of the paroccipital, but on account of the character of the 

 dentition and of the limbs.^ 



The third character which I have pointed out as distinguishing the 

 suborders of Squamata is the difference in the mode of articulation of 

 the quadrate bone with the adjacent cranial elements. In tbe Sauria 

 it articulates with the exoccipital, being also in contact with the par- 

 occipital and the suprateniporal. The contact with the paroccipital is 

 insignificant, owing to the small size of that element; and that with 

 the suprateniporal is only important where that bone is well developed. 

 In many Sauria it is feeble or wanting. In the Pythonomorpha and 

 Ophidia on the other hand the (quadrate articulates with the parocci- 

 pital, sometimes touching the supratemporal in the former. In some 

 of the degraded Oj)hidia, as the Typhlopidic and Stenostomidae, the i^ar- 

 occipital is not distinct, so that the quadrate appears to rest on the exoc- 

 cipital and the petrosal. It will, however, be necessary to subject these 

 types to more searching investigation before it can be known that the 

 paroccipital is absent. 



As exceptions to the rule in the Sauria, Boulenger has pointed out that 

 the quadrate does not reach the exoccipital in the Agamid genus Ghlam,y- 

 dosaurus,^ and I have found the same condition in Phrynocephalus.^ 



4. PHYLOGENY. 



From this point of view the Ophidia and Pythonomorpha must be 

 traced to some type in which the paroccipital bone is less remote from 

 the brain case than is seen iu the Sauria, where it has become a mere 

 rudiment. Such a phylogeny would be expressed as follows. An 

 investigation of the Dolichosauria of the Cretaceous might yield inter- 

 esting results. 



Sauria. Pythonomorpha. Ophidia. 



Common ancestor, with ambulatory limbs and sessile paroccipital. 



' Proc. Zool. Soc. London, 1891, p. 117. 

 "Ann, Mag. Nat. Hist., XVI, 1895, p. 367. 

 3 American Naturalist, 1896, XXX, p. 150. 



