148 University of Kansas Geological Survey. 



been somewhat greater, but the differences are nevertheless 

 very marked. On the distal border, the thickened, smooth and 

 nearly flat articular border for the radius looks very obliquely 

 outward, more so than in any other form ; it meets the surface 

 for the ulna in a rounded angle. At the proximal (outer) 

 rounded margin of the articulation begins the prominent, styli- 

 form radial process, directed outward in the plane of the bone ; 

 it is flattened from above downward, and its tip was covered 

 with cartilage. The ulnar condylar process is stout and thick, 

 its surface subtriangular in outline, looking downwards, in- 

 wards and distad. The surface of the bone on the outer ( ra- 

 dial ) side is roughened. The free ulnar border of the bone is 

 much longer than the radial, and more deeply concave. The 

 radial border forms a short notch between the upper angle of 

 the bone and the radial process. The pectoral process is more 

 distinctly differentiated than in Mosasaurus, is situated nearer 

 to the radial side of the bone, and has, at its upper part, a dis- 

 tinct cartilaginous surface, separated from that of the head of 

 the bone and looking more downward. The dorsal surface of 

 the bone is convex transversely, and gently concave along the 

 middle longitudinally. A humerus of Clidastes ivestii, from the 

 Fort Pierre, in the collection, has not been subjected to com- 

 pression or distortion. The shapes of the two ends are shown 

 in plate xxxix. It is probable that these outlines represent 

 the general Clidastes type. 



Brachysaurus overtonii. The humerus of Brachysaurus differs 

 markedly from that of all the other forms. It is stout and 

 broad. Its proximal end is angulated near the middle, both 

 sides sloping away from the angle, much as in Tylosaurus. The 

 ulnar side is the longer and thinner of the two. The distal bor- 

 der is much elongated, and more convex from side to side than 

 in the other genera. Its greater thickness is on the radial side, 

 whence the border turns proximad to near the middle of the 

 bone, leaving only a very short, moderately deep notch between 

 it and the superior angle. There is no radial process. The 

 ulnar side of the distal margin is considerably thickened as far 

 as the place where it is reflected downward, where it is contin- 



