115 



posterior decurvature of the upper portion of Ihc quadrate bone, which thus 

 partially incloses the auricular meatus in a manner not seen in lizards and 

 serpents. To the orders of the other primary divisions Ichthyopterygia and 

 Archosauria, as the Ichthyosauridce and Crocodilia, there is not the least affinity. 



The remaining characters above enumerated ally the Pythonomorpha to 

 both serpents and lizards. As there are many Lacertilia without limbs, and 

 some serpents with them, their presence in this order is irrelevant in this 

 connection, especially as the arches supporting them are most like those of 

 tortoises and Plesiosaurs. In the absence of sacrum, it resembles both the 

 associated orders, though the same character is universal in serpents, as the 

 presence of limbs is general in the lizards. The manner in which the opis- 

 thotic bone projects from the embracing bones is a decidedly ophidian feature, 

 while the production of the exoccipital and prootic is lacertilian. The posi- 

 tion of the stapes and absence of quadrato-jugal arch are characters common 

 to both orders. The lateral decurvature of the parietal is a character of the 

 Ophidia, and not of the Lacertilia; while the failure of this bone and the 

 frontal to complete the cranial chamber in front is a lacertilian feature. The 

 composition of the posterior part of the lower jaw is like that in the lizards 

 in the distinctness of the articular and surangular bones ; in the presence of 

 chevron-bones, it differs from snakes * the atlas and axis are those of both 

 snakes and lizards, and entirely different from those of Crocodilia. In the 

 absence of true roots of the teeth, these animals differ from all Lacertilia, and 

 more nearly resemble, without being identical with, the Ophidia. Thus it is 

 evident that the Mosasauroids and their allies represent an order of reptiles 

 distinct from any other, and I have called it Pythonomorpha, from those points 

 in which it resembles the Ophidia. 



There are many other characters common to all the known species of 

 this division, which are not probably of ordinal character, and which I pro- 

 ceed to enumerate. Among them will be found some known elsewhere in 

 the Ophidia, and others which relate them to lacertilian groups. 



Cranium. 



The skull, in the known species of this order, is wedge-shaped, and 

 generally elongate. Posteriorly, it presents postfronto-squamosal and parieto- 

 qualrate arches; in some species, also, a malar arch is thought to exist. 



Teeth. — These exist in a single row on the dentary, palatine, and 



