152 University of Kansas Geological Survey. 



outer part is thin and moderately concave, and reaches the full 

 length of the bone, from the thickened proximal to the distal 

 angle. The bone has no articulation distally, the single carpal 

 bone being set in a plate of fibro-cartilage, which is attached to 

 the roughened border of the forearm bones. 



Ulna. 



Mosasaurus horridus. The ulna in Mosasaurus is a less broad 

 bone than is the radius, but is rather stouter in its proportions. 

 The proximal end is stout, thick, transverse, and rectangular, 

 the surface somewhat cupped and smooth ; in outline subtri- 

 angular, with the inner angle produced more than the outer. 

 The distal extremity is less expanded than the proximal, and 

 shows three facets for close union with carpal bones, separated 

 from each other by slight angles, that on the outer side the 

 most angulated. The middle facet, the largest, is nearly trans- 

 verse to the long axis of the bone. The inner border is thicker 

 than the outer and more deeply concave, the greatest concavity a 

 little beyond the middle of the bones ; the border extends from 

 the sharp angle of the carpal articulation to the slightly rounded 

 angle of the humeral. On the inner side the border is shorter, 

 thinner, and less deeply concave, extending from the angle for 

 the surface of the sesamoid bone to the rounded, thinned, ole- 

 cranon expansion on the inner side of the proximal end. The 

 shaft of the bone is twisted somewhat, so that the inner border 

 at the proximal end is turned downwards. The dorsal surface 

 of the bone is markedly concave longitudinally and transversely 

 throughout the most of its extent, the plane of the proximal 

 end twisted dorsally on the inner side. On the palmar surface 

 the bone is strongly convex transversely and but slightly con- 

 cave from end to end. 



Clidastes velox. The ulna in this species differs only in minor 

 details from the same bone of Mosasaurus horridus. It is more 

 slender and less stout, the proximal articulation is placed a little 

 more obliquely to the long axis of the bone, the olecranon proc- 

 ess is smaller, and the corresponding inner border longer. The 

 distal articulation is more oblique outwardly and there are but 



