l68 KANSAS UNlVERSnV QUARTERLY. 



of sj;)ecialization in the Pythonoinorpha as well as its latest develop- 

 ment. The genus Cluiastes occurs in the Ft. Pierre Cretaceous, as 

 I have already shown, and as a recently received specimen from 

 Colorado indicates. A comparison of the rijnire of the paddle here 

 given with those of C. tcIox and C. IVcsNi previously given by the 

 writer* will show certain differences of interest. In C. rv/o.v, from 

 the Niobrara, the second carpal bone of the first row is separated by 

 a distinct interval from the radius, the scaphoid showing a distinct 

 interosseous border. At its other extremity it scarcely touches the 

 ulna and has no articular facet for that bone. In C. J]'i's/ii, from 

 the lowermost Ft. Pierre, the free border of the scaphoid is lost and 

 the second bone articulates with the radius, and shows a beginning 

 of an articulation with the ulna. In M. horridiis, from the Upper 

 Pierre, the articulation with the radius is yet greater and that with 

 »^he ulna is pronounced. In this last species the humerus is remark- 

 ably stout and the tuberosity of the proximal end rises higher above 

 the head than in Clidastcs. Altogether these differences show a 

 progressively more powerful paddle. This Clidastcs type of the 

 paddle was already apparent from tlie figures given by Feidy (^Cre- 

 taceous Reptiles of the United States, PI. iv). 



The affinities between these two genera, it is thus seen, are much 

 greater than those of either with any other. They offer certain 

 structural peculiarities in common that separate them readily from 

 other Mosasaurids, and it has long seemed to me, that were these 

 peculiarities those of existing lizards there would be no hesitancy in 

 assigning to them a family value. At present, but one family, 

 Mosasaurids, is recognized in the order, Plioplatecarpida?, founded 

 chiefly upon a supposed sacrum, having been given up by its author. 

 The genera now recognized as belonging to the Pythonomorpha are 

 as follows: 



Mosasaurus Conybeare, 1S24. Europe, North America. 



Clidastes Cope, 1869. North America. 



Baptosaurus Marsh, 1S69. North America. 



Platecarpus Cope, 1869. North America, New Zealand (?). 



Tylosaurus Marsh, 1872. North America. 



Sironectes Cope, 1875. Kansas. 



Plioplatecarpus Dollo, 1882, Europe. 



Hainosaurus Dollo, 1885. Europe. 



Prognathosaurus Dollo, 1889. Europe. 



These eight or nine genera seem well established, although I have 

 some doubts of the validity of Sironectes, and it is not improbable 

 that the genus Holosaurus Marsh may yet be found valid, though not 

 *Kaiis. Univ. Quarterly. 1, 1892, p. 1, plates i-iv. 



