174 University of Kansas Geological Survey. 



This species was the first of the Mosasaurs described from 

 Kansas. "The original description was based upon material 

 in the Museum of Comparative Zoology, Cambridge, Mass., 

 brought by Prof. Louis Agassiz from the Cretaceous beds in 

 the neighborhood of Monument, Kan., and near the line of the 

 Kansas Pacific road." The locality thus given by Cope is not 

 exact. The specimen was undoubtedly found in the vicinity of 

 Monument Rocks, the old overland stage station, which is not 

 near the railroad, while the station, Monument, is not near any 

 Cretaceous outcrops. The species is the most common of this 

 genus, and has been found at nearly all horizons in the Nio- 

 brara beds. The characters of the species have been fully 

 given in the preceding descriptions, and need not be repeated 

 here . 



Tylosaurus dyspelor. 



Lindon dyspelor Cope, Proc. Amer. Phil. Soc, 1870, p. 574; 1871; Cret. 



Vert., 167, pis. xxviii, ff. 1-7; xxix, xxxiii. 

 Rhinosaurus dyspelor Marsh, Amer. Journ. Sci., June, 1872. 

 Tylosaurus dyspelor Leidy, Ext. Vert. Fauna West. Terr., 271, pi. xxxv, 



ff. 1-11; Merriam, Ueber die Pyth. der Kans.-Kreide, 14. 



This species, the largest of the Kansas Mosasaurs, was origi- 

 nally described from a specimen obtained from the Niobrara 

 chalk near Fort McRae, N. M. It is the only species of the 

 group found in Kansas that is known to occur elsewhere. 



The differences that Cope gives for the species are as follows : 

 "The palatine bones are more slender anteriorly, and the outer 

 edge descends lowest in a ridge ; in L. proriger, the inner is pro- 

 duced downward as a longitudinal rib. In this species there are 

 eleven teeth ; in that one, nine. The quadrate bone of L. proriger 

 presents a longer internal angle, and more prominent internal 

 ridge, with smaller space inclosed by the basis of the great ala." 

 These characters are not correct. The "palatines," i.e., the 

 , pterygoids, are quite alike anteriorly. In a specimen of T. dys- 

 pelor I count eleven teeth, as stated by Cope ; in two specimens 

 of T. proriger I find ten teeth, and I do not doubt but that in 

 others there may be eleven, or that in specimens of T. dyspelor 

 there may not be more than ten. This variation is also affirmed 



