546 Mr. R. W. Hooley on the 



Gkoup B. 



J. a. 6, 35. This example was figured by Owen "^ and also 

 by Seeley f. It differs from Orn'ithodesmus latidens in tlie 

 circular pit on tlie articnlar surface being postaxial, while in 

 the Atherfield specimen it is nearer the preaxial. The pre- 

 axial or radial area of the Cambridge specimens^ as described 

 by Owen J, " shows a sligbtly convex surface occupying its 

 major part, and a small well-flefined flat surface placed 

 obliquely.^' The " slightly convex snrface^^ becomes more, 

 convex ventrally as it nears the flat oblique surface. With 

 a part of the former and the whole of the latter the radius 

 articulated ; but the dorsal moiety of the " slightly convex 

 surface^' was a portion of the ulnar articulation, which is 

 continued round the dorsal margin to the postaxial edge 

 (ulnar side), where it becomes an oval concave surface. The 

 ulnar tubercle is placed on the ventral l)order only, and not 

 on the postaxial, as in Orriithodesmits latidens. By nos. 20, 

 29, 33, and 34 it is seen that in this group there is no trans- 

 verse valley, but that the ulna apparently occupied the whole 

 of the transveise diameter of the articular end. 



Group C. 



The most perfect distal end of this group is J. a. 6, 36. 

 It is crescentic, with the convexity on the dorsal side. The 

 articulation exhibits a radial and median convexity, with a 

 depi'ession between them, forming a trochlea. On the 

 ventral marjjin of the postaxial side there is a tubercle 

 directed distally, and dorsal to this an oval concave facet, 

 obliquely placed and looking outwards. On the ventral 

 surface, between the horns of the crescent, there is a deep 

 concavity, and, as the radial and ulnar condyle both have a 

 flat facet looking inwards, it is probable that the radius 

 articulated with both these. 



The type of ulna shown on tablet J. a. 9, no. 1, we believe 

 to belong to this group, because of its similar articular 

 surfaces. 



It is highly probable that the proximal ends of Groups A, 



* R. Owen, Rep. Cret. Form. (Mon. Pal. Soc. 1831), Suppl. i. pi. iv. 

 figs. 1-3. 



t IT. G. Seeley, ' Ornithosauvia,' 1870, pi. iv. fig-. 14. 

 X R. Owen, loc. cit. p. 16. 



