250 KANSAS UNIVERSITY SCIENCE BULLETIN. 



seems to be absolutely nothing left except the zygosphenes. 

 The number of pterygoid teeth varies between eight and six- 

 teen. The absence of the coracoid emargination in C. tortor 

 prevents its use as a generic character. 



So long as there are no indications of a zygosphene in certain 

 species and a well-developed one in others, the character may 

 remain as the sole difference between the two genera ; but I 

 suspect that, as in Platecarpus, species will be discovered in 

 which this character is rudimentary or incomplete. In such 

 case the genus Clidastes must be merged into Mosasaurus. 



An examination of the type specimen of Edestosaurus wymani 

 Marsh discloses the fact that the species is not at all distinct 

 from Clidastes velox. 



The known Kansas species of Clidastes are the following : 



C. velox Marsh. 



C. dispar Cope. 



C. stenops Cope. 



C. westii Williston. 



C. cinerianus Cope. 



C. liodontus Merriam. 



The last two are yet very imperfectly known and may be 

 identical with each other ; or, it is possible that one or the other 

 is identical with some one of the others. 



Orbitosphenoid of the Mosasaurs. 



In plate IV, fig. 5, of my report upon the mosasaurs of Kan- 

 sas (Univ. Geol. Surv., vol. IV), there is given an enlarged 

 picture of an undetermined bone of Platecarpus. At the time I 

 could reach no certain conclusion as to its position in the 

 skeleton, and preferred to leave it without comment rather 

 than to guess at its position. In the specimen of (Clidastes 

 stenops just described, two similar bones, differing only in being 

 a little more slender, were found in the matrix lying upon the 

 axis, aud another attempt was made to determine them. That 

 they could not be hyoid bones was certain, since they differed 

 too much from the real hyoid of Tylosaurus; nor could they be 

 epipterygoids, bones described by Marsh, but of which I had 

 been very uncertain, since there are no places on the pterygoids 

 and petrosals to admit of their attachment. An examination, 

 aided by Mr. Martin, of the material in the University of Kan- 



