Merriam.] 



Triassic Tchth ydpterygia . 



81 



corner of the upper side is separated from the remaining surface 

 by a well-marked groove, running from the posterior emargina- 

 tion to the posterior eud of the radial border. The radial border 

 is considerably longer than the ulnar and is slightly thicker, 

 excepting the posterior portion of the latter, which is added to 

 by a prominence on the distal end of the. upper surface. 



The radius is a quadrate element, somewhat wider than long 

 (width 110-115 mm., length 95). The proximal margin is 

 nearly straight, the distal slightly convex, the posterior concave, 

 and the anterior is marked by a deep, narrow notch, like that in 

 the longipinnate Ichthyosauria. The ulna is considerably smaller 

 than the radius in all of its dimensions (length 71 mm., width 85) 

 and runs out to a comparatively thin edge on its posterior 

 border. Its proximal margin is nearly straight, the small portion 

 of the distal edge present is convex, the posterior side is also 

 convex. The anterior border is slightly concave. 



The form of the adjacent margins of the radius and ulna 

 shows that they must have been separated by a considerable cleft. 

 Their positions with reference to the humerus, causing them to 

 diverge distally, would probably increase the distance, so that 

 there would be quite a wide space between them. 



The radiate is somewhat larger than the ulna and might have 

 been mistaken for it, had not their positions in the matrix been 

 such as to preclude the possibility of such a confusion. The 

 lower end of the bone is broken off, but as the break is evi- 

 dently below the middle the absence of a notch on the portion 

 present may be taken to indicate that the anterior margin was 

 entire, since the emargination always occurs in the middle. If 

 notching were caused by shortening of the shaft, as suggested 

 by Lydekker, it could easily be present in the radius without 

 having developed in the carpus. 



Resting in the angle between the distal ends of the radius 

 and ulna and the proximal extremity of the radiate was an 

 elliptical ossicle, which possibly represents the intermedium . The 

 border is deeply concave and was evidently surrounded by a 

 thick layer of cartilage. A careful examination of the adjacent 

 angles of the radius and ulna reveals no sign of a "facet for 

 contact with an intermedium.. The posterior, distal corner of the 



