98 University of Kansas Geological Survey. 



Baur does not insist upon uniting the Mosasaurs in the same 

 ultimate division as the rest of the Lacertilia, or any of the living 

 forms, but does insist that they be placed under the Lacertilia. 



In criticizing the first of these papers by Baur, Boulenger, 

 the distinguished herpetologist, took the position, with Cope, 

 that the Pythonomorpha constitute a distinct suborder of the 

 Squamata, basing his views chiefly upon the limbs. He says : 

 "Does this mean that limbs as strongly modified as those of 

 the Monitors can have been modified into the paddles of the 

 Mosasaurs? A glance at the figures suffices to refute such a 

 theory." He defined the Pythonomorpha as having "nine or 

 ten cervical vertebrae. Extremities paddle shaped, with hyper- 

 phalangy." In the three Kansas genera of the Mosasaurs de- 

 scribed in the present work there are never more than seven 

 cervical vertebrie. While hyperphalangy does occur among 

 the Mosasaurs, there are some forms in which this is so in only 

 a slight extent or not at all. In all the forms the " fifth meta- 

 tarsal is reduced in length and strongly modified," another 

 lacertilian character given by Boulenger. 47 



The latest definition of the Pythonomorpha given by Cope 4S 

 is as follows : 



Aliaphenoid modified as epipterygoid or wanting, leaving brain-case open ; 



parietals flat : an interclavicle and clavicle ; teeth with dentinal roots, 



Lacertilia. 

 Epipterygoid present ; parietals decurved, partially inclosing brain-case ; no 



clavicle nor interclavicle; teeth with osseous roots Pythonomorpha. 



No epipterygoid ; brain-case inclosed in front; no clavicle nor interclavicle ; no 



fore limbs ; teeth rootless Ophidia. 



Dollo has recently affirmed the presence of a distinct interclav- 

 icle in the Mosasaurs, first discovered by Marsh. I have never 

 seen such a bone in the material that has been accessible to me. 



Following the foregoing papers and discussions appeared a 

 paper by Dollo, 49 in which he summed up his views as follows : 



" En resume, je suis done d'accord avec M. Boulenger pour regarder 

 les Mosasauriens conmie un sous-ordre distinct des Squamata. 



47. Boulenger, Notes on the Osteology of Heloderma horridurn and H. suspectum, with Re- 

 marks on the Systematic Position of the Helodermatidse and on the Vertebrae of the Lacertilia, 

 Proc. Zool. Soc. Lond. 1691, pp. 109-1U. 



48. Syllabus of Lectures on Geology and Paleontology, pt. in, 45, 1891. 



49. Bulletin Soc. Belg. de Geol., vi, 251, 1892. 



