AVilliston.] Mosasaurs. 99 



" Je pense, comme lui, que les Lacertiliens actuels (meme les Var- 

 anidce) sont trop specialises pour representer la souche des Mosasau- 

 riens. 



"Je crois, comme mon collegue du British Museum, que cette 

 souche nous est fournie par les Dolichosauriens. 



' Mais je ne puis admettre que ceux-ci soient les ancetres des Lac- 

 ertiliens. des Ophidiens, et des Rhiptoglosses." 



Of course no one can for a moment suppose that the Mosa- 

 aurs have not descended from terrestrial fissiped reptiles. The 

 great variations in the type of the limbs among the Mosasaurs 

 do not permit such exact comparisons as M. Dollo makes. 



The latest discussion on the affinities and systematic position 

 of the Mosasaurida? will be found in the papers cited below 50 

 by Professors Cope and Baur, dealing especially with the ele- 

 ments supporting the quadrate. This controversy in brief was, 

 on the part of Cope, that the paroccipital was a distinct element, 

 and not fused with the exoccipital, which did not support the 

 quadrate at all. Baur contended that the paroccipital was fused 

 with the exoccipital, and that the separate element called the 

 paroccipital by Cope is in reality the squamosal. Further, 

 Baur contended that the exoccipital of Cope, his paroccipital, 

 did not at all support the quadrate, in the Iguanidse, while 

 Cope asserted that such was always the case. It is true that 

 in Varo/nus the exoccipital of Cope does, in a measure, support 

 the quadrate to a greater degree than I have ever observed 

 among the Moasaurs. It is also true that the exoccipital (Cope) 

 does in many cases help form the quadrate articular surface in 

 the Mosasaurs. 



The more important cranial differences from Varanus are as 

 follows : The premaxillary of Varanus is flattened, and the con- 

 joined nasals are united by a distinct suture. There are eight 

 premaxillary teeth. The nares are much larger, the prefrontals 

 smaller, the palatines smaller, and its anterior process longer. 

 The lachrymal bone is larger. There is a supraciliare present, 

 wholly wanting in all Mosasaurs. The frontal bones are united 



50. Cope, Amer. Nat., Sept. 1895; Nov. 1895, p. 1003; Febr. 1896, p. 147. 



Baur, Amer. Nat., Nov. 1895, p. 998; Febr. 1896, p. 143; Apr. 1896, p. 327. 



