124 University of Kansas Geological Survey. 



Prosquamosal (quadraiojugal, squamosal). 



Clidastes. The prosquamosal is an elongate bone, dilated 

 posteriorly. The posterior end is turned downward, with an 

 excavation on the lower side for the outer part of the articula- 

 tion for the quadrate bone. On the inner side distally it ar- 

 ticulates with the squamosal, the anterior process of which 

 extends forward as described below. The anterior end forms 

 the inner and upper part of the arch, extending nearly to the 

 anterior end of the arch, but not reaching the jugal. It is 

 deeply grooved on the outer superior side for the postfrontal, 

 which extends to a point nearly as* far back as the surface of 

 the quadrate. It articulates with the quadrate, squamosal, and 

 postorbital. 



Platecarpus. PL xxvi, f. 4. The prosquamosal differs from 

 that of Clidastes in its relations to the squamosal. In Clidastes 

 the upper border of the posterior end is convex and scarcely 

 elevated above the body of the bone, or, if so, only slightly. In 

 Platecarpus there is a flat process on the upper part, uniting 

 with the squamosal, which does not send a process forward. 

 The bone anteriorly reaches as far forward as the jugal process 

 of the postorbital, and touches the jugal. 



Tylosaurus. The prosquamosal in this genus articulates with 

 the jugal, as in Platecarpus. It differs from Platecarpus in the 

 more rounded, wing-like process on the upper side distally, 

 which is pointed in the former and scarcely at all projecting in 

 Clidastes. The bone, also, is more curved downward at the pos- 

 terior end in this genus. 



-Ectopteryg'oid (or transverse bone). 



The ectopterygoid has never been found in Clidastes, and in 

 all probability it is very incompletely ossified in this genus, since 

 the slender jugal shows only a small articular surface for it, or 

 none at all. 



In Platecarpus (pi. xxv, ff. 4, 5) the bone varies considerably 

 in shape in different individuals, the jugal branch being longer 

 or shorter. It is somewhat L-shaped, with the shorter branch 



