Williston.] Mosasaurs. 125 



broad, and with an oblique sutural surface on the under side 

 for union with the expanded end of the ectopterygoid process 

 of the pterygoid. The anterior branch is slender and more or 

 less pointed. Its outer surface is flattened and roughened for 

 sutural union with the jugal. It does not reach to the maxilla. 

 In Tylosaurus the bone differs only in being a little more 

 slender ; the pterygoid end less broad. It articulates with the 

 jugal in same way as in Platecarpus, not reaching the maxilla. 



Quadrate. 



Clidastes. PI. xxiv, f. 7. From below, the articulation of 

 the quadrate is a little longer from side to side than antero-pos- 

 teriorly. In the former direction it is somewhat concave, with 

 a median convexity. From without, the rim of the ear cavity 

 forms a nearly complete circle, the diameter a little greater from 

 above downward , and extending to the tip of the suprastapedial 

 process. Its lower margin terminates in a small, roughened 

 process, nearly opposite the tip of the suprastapedial process, 

 bur external to it, and the articular surface of the lower end of 

 the bone is beveled so that its upper margin nearly coincides with 

 the lower border of the ear cavity. At the upper extremity the 

 articular surface is convex in both directions, more strongly so 

 antero-posteriorly. Anteriorly the articular surface divides into 

 two processes, of which that on the upper border of the ala, the 

 alar process, is the longer and narrower. Back of the junction, 

 the sides of the surface are nearly parallel to opposite the top 

 of the auditory notch, where it is narrowed at the expense of 

 the outer side, which is depressed and roughened. The supra- 

 stapedial process is directed downward and somewhat inward, 

 reaching a little below the middle of the bone. On the inner 

 side the suprastapedial process is excavated above, and toward 

 the tip there is a smooth, oval, articular surface looking inward. 

 The inner border is nearly straight from above downward, with 

 a raised, narrow ridge beginning below the meatal pit and con- 

 tinuing nearly to the inferior extremity. In front and slightly 

 below the pit there is a distinct roughening on the convex bor- 

 der. The roughened projection on the posterior side below is 



