102 University of Kansas Geological Survey. 



and the rnaxilla, on either side, there is a long, narrow vacuity, 

 situated in part below the external nares. The palatines curve 

 downwards to articulate with the pterygoids, so that the teeth of 

 the latter are in a lower plane than those of the rnaxillee. 



The pterygoids are elongate, curved bones with four processes. 

 The anterior, obliquely flattened process articulates with the 

 inner side of the palatines and is separated narrowly from its 

 mate at the extremity. The ectopterygoid process, thicker and 

 stouter, is directed somewhat upwards, its rugose and dilated 

 extremity attached to the transverse bone. The dentigerous 

 portion is prolonged into a small, flattened process, which lies 

 under the basipterygoid process of the basisphenoid, nearly in 

 contact with that of the opposite side and close to the under 

 surface of the basisphenoid. The long, flattened, involute pos- 

 terior process is curved outward and downward to articulate 

 with the inferior inner angle of the quadrate. Its roughened 

 end fits closely to a corresponding surface on the quadrate, and, 

 while the union may not be rigid, it cannot admit of much 

 motion. 



In the following detailed descriptions I have used for com- 

 parison skulls of Clidastes velox, Platecarpus coryphaeus, Mosasaurus 

 horridus, Tylosaurus proriger, and an incomplete one of Bracliy- 



saurus overtoil i : 



Premaxillo-iiasals. 



Clidastes velox. The premaxillary is characteristic of the 

 genus. The anterior, expanded portion is about as long as wide, 

 forming a broad, short cone, extending only a short distance in 

 front of the teeth, with the apex rather sharp. The borders for 

 articulation with the inaxillee pass inwards obliquely, the width 

 of the superior surface between the maxillae to the anterior end 

 of the nares being nearly equal throughout, the sides almost 

 parallel. The surface is lightly and delicately sculptured 

 above, with an obtuse, low, median convexity. At the begin- 

 ning of the nares, the superior surface rapidly narrows to form 

 a vertical plate separating the openings. At the posterior ex- 

 tremity the conjoined nasals dilate to overlap the narrow an- 

 terior projection of the frontal. On the under side tl;ere are 



