Willistox.] Mosasaurs. 203 



ilium is less sigmoid than in E. dispar, and the ischium more 

 expanded distally. The pubis appears to have had a more 

 prominent anterior process. The articular ends of the anterior 

 caudals are vertically oval." 



The species differs, according to the author, from C. tortor 

 and E. dispar, in "the less number of the pterygoid teeth and 

 in other characters." The absence of one tooth in the ptery- 

 goids is not of specific importance. If the other characters had 

 been of any importance the author would have stated them. 

 The shape of the pelvic bones, by reference to his figures, one 

 will see to be of trivial importance, and all might easily have 

 been the result of imperfect preservation. Until these "other 

 characters" are forthcoming, it will be quite safe to consider 

 C. rex as a synonym of C. tortor. 



Clidastes medius Merriam was based upon the shape of the 

 prefrontal bone. "Die meisten knochen stimmen mit den 

 entsprechenden von C. velox und C. tortor uberein," but the 

 prefrontal " nicht so weit in der Entwickelung zu einer einfachen 

 horizontal Platte vorgeschritten ist." 



In the absence of further differences and figures, I think it 



may be safely assumed that the difference of the prefrontal 



bone has been due to imperfect preservation rather than to a 



specific structure. 



Clidastes wymani. 



CUdastes wyrnani Marsh, Amer. Journ. Sci., June, 1872, plate n, f. 1. 



This species was based upon two specimens — one including 

 the chevron caudal vertebrae ; the other, parts of the skull and 

 anterior vertebra?. It is, of course, not at all certain that the 

 two skeletons belonged to the same species. 



" The specimens indicate a small reptile, very near C '. propython 

 in size, but differing from that reptile in several important par- 

 ticulars. One of the most noticeable of these is the form of the 

 muzzle, which in the present specimen has a short and obtuse 

 extremity, not unlike that of Liodon proriger Cope (Tylosaurus) . 

 The basioccipital has the condyle deep vertically, and only a 

 shallow groove on the upper surface for the neural canal. The 

 quadrate has the postero-superior process free at its lower ex- 



