115 



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

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

 serpents. To the orders of the oti^^r primary divisions IcIitJn/opteri/g'ui and 

 Archosnur'ia, as the Ichthyosauridce and Crocodilia, there; is not the least affinity. 



The remaining characters above enumerated ally the Pythonomorpha to 

 both serpents and lizards. A's there are many Laccrtilla 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- 

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

 while the production of the exocci[)ital and ])ro5tic is lacertilian. The posi- 

 tion of the stapes and absence of quad rato-ju gal arch arc characters common 

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

 Ophidia, and not of the Lacertilla; while the failure of this l^onc and the 

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

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

 in the distinctness of the articular and surangular Ijones ; 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 CrocodUia. In the 

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

 more nearly resemble, without being identical with, the OpJiidln. 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 tlx; Opiiidia. 



There are innny other eliaracters common to all the known species of 

 this division, which arc not pn)lial)]y of ordinal cliaractcr, and wliieli T \\\o- 

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

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



Craniu7n. 



The skull, ill tlie known species of this ordfM-, is wedge-shaped, and 

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

 qualrate arches ; in some spccif^s, also, a malar arch is thouiriit to exist. 



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



