116 University of Kansas Geological Survey. 



of the ectopterygoid process on the upper side in front of the 

 notch between the quadratal and basisphenoid process there is 

 a rounded pit for the epipterygoid. The ectopterygoid process 

 is much dilated obliquely at its extremity, sometimes dilated 

 near its base in front so as to constrict the inclosed notch. The 

 palatine process is flattened, ending in a narrower extremity. 

 The teeth begin posterior to the end of the palatine. The teeth 

 are small, much curved, somewhat flattened and striate. 



Tylosaurus. In Tylosaurus the pterygoid resembles that of 

 Platecarpus. The anterior dentigerous portion is stouter and 

 less flattened, the part in front of the teeth for union with the 

 palatines thinner and less broad. The teeth begin further for- 

 ward, as in Clidastes, and not back of the palatines. The ecto- 

 pterygoid processes are relatively stouter and less contracted at 

 the base. The basisphenoid process is broader and shorter, and 

 the teeth do not extend as far as its base, while in Platecarpus 

 they reach two-thirds of the distance to its tip. The quadratal 

 process is less expanded distally, and is relatively shorter than 

 in Platecarpus . The bone altogether is less slender. There are 

 ten teeth. 



Parietal. 



Clidastes. The coossified parietals have a broad, anterior, 

 transverse border, concave sides, limited by sharp margins, the 

 parietal crests, and long, thin, flattened parieto-squamosal proc- 

 esses, reaching outward and backward from the posterior angle 

 to the outer part of the suspensorium. Posteriorly, on either 

 side, the upper surface is continued into a pointed projection, 

 which forms the upper margin of the base of the parieto- 

 squamosal process. The margin in the middle behind is thinned, 

 rugose, beveled, and with a notch in the middle. Anteriorly 

 the stouter lateral processes or wings pass outward to form the 

 anterior lateral border of the supratemporal fossae, connecting 

 with the postfronfcals. They are convex from above downwards, 

 and limited on the inner part by a sharp overhanging ridge, 

 the beginning of the parietal crests. The pineal foramen is 

 small, and situated a short distance back of the front margin of 



