l66 KANSAS UNIVERSITY QUARIKRLV. 



which can not possibly be separated from vl/. maximiliani g^ntncaWy, 

 has but eight teeth on the pterygoid, as in M. camperi. The character 

 of the premaxiHary is valid, but not generic. 



The genus Plc-rycol/asaitn/s, as defined by Dollo, thus rests upon 

 errors, and has been rejected. Nevertheless, I am not sure but that 

 (xoldfuss' species and the one described in the present paper are 

 entitled to generic separation from Mosasaunn. This however, in 

 the absence of more complete kno\vle<lge of the typical Mosasaurus, 

 I cannot decide at present. Dollo has recently shown that Liodon 

 Owen is a synonym of Mosasaurus. If so, it seems apparent that 

 the present species is not of the same genus, for certainly the figure 

 of the skull of L. anceps given by Owen shows a distinct difference 

 from that figured herewith. 



During the past summer, the University of Kansas Geological 

 Expedition to the Had Lands of Dakota was fortunate in obtaining, 

 among other valuable material, what I believe to be the most perfect 

 skull of a Mosasaur yet known in any museum. The specimen, 

 which includes nearly the entire skull, the larger part of a front 

 ])a(ldle and about forty vertebrae, has been mounted in the Univer- 

 sity Museum and figures of this skull as mounted, are given in the 

 accompanying plates, 'fhe only bone of the skull that is missing is 

 thejugalof the right side; that of the left side was dislocated and 

 enclosed in the hard matrix of the orbit, from which it has not been 

 extricated. Like most specimens from the Pierre Cretaceous it was 

 enclosed originally in a hard, nodular matrix of a bluish color, from 

 which the larger part of the skull had gradually been oxidized, 

 leaving the bones in the utmost perfection. A part of the bones, 

 however, " waren von einem sehr harten, feinkornigen, dichten 

 Kalksteine mehrere Zoll dick umgeben, welcher im Inneren grosserer 

 Stiicke blaulichgrau, weiter nach aussen ochergelb und weicher ist" 

 (Goldfuss), and which has been removed with tlifticulty. 



As cleaned and mounted, the specimen gives a most remarkably 

 vivid impression of the skull of the living animal. An extended 

 discussion of its structure and relations is reserved for a later paper.- 



Tlie specimen, though closely related to J/, maximiliani, clearly 

 indicates a distinct species, somewhat smaller than J/, camperi, and 

 fully a third larger than AT. nux.ximiliani. It offers more tangible 

 differences from the latter species, in the number of the pterygoid teeth 

 and in the much greater width of the posterior part of the mandible. 

 Some of the more important measurements of this skull, whose 

 species I will call J/, horridus, are given below, in comparison with 

 corresponding measurements taken from the plates of M. maxiuiiliani 

 by Goldfuss. 



