APRACTOCLEIDUS TERETIPES. 



621 



is covered with rugosities and plications which rise from the smooth shaft and 

 spread fanwise over the expansion. These terminate in a line of small depressions 

 situated about 1 cm. from the margin, and a comparatively smooth strip is left on 

 the -distal and post-axial borders. The distal expansion bears four distinct facets 

 for the articulation of four bones — radius (r.), ulna (u.), pisiform (p.), and post-axial 

 accessory ossicle (a.). The facet for the radius is the largest, and it is slightly 

 concave. The facets for the ulna and pisiform are differentiated by a slight salient, 

 and almost at right angles to the line of the last two there is a convex facet, about 



mc.V. 



Text-Fig. 8. 



Proximal portions of fore paddles : A,* left fore paddle of Tricleidus seeleyi, from above. (Type specimen K. 3539, \ nat. 

 size.) B, left fore paddle (outer side) of Apractocleidus teretipes. (Type specimen V. 1091, about I nat. size.) C,* right 

 fore paddle (ventral face) of Cryptoekidus oxonicnsis. (R. 2412, £ nat. size. ) a. , accessory ossicle ; h. , head of humerus ; 

 hum., humerus ; int., intermedium ; wc.V., fifth metacarpal : m.r., ridges for muscle insertion ; p., pisiform ; r., radius ; 

 rod., radiale ; la., tuberosity of humerus ; u., ulna ; uln., ulnare. 



* A, after Andrews, 1909, p. 420, fig. 2. C, after Andrews, 1910, p. 182, text-fig. 90, C. 



4 cm. long, on the post-axial margin, for the articulation of an accessory ossicle. 

 The epipodial bones resemble those of Tricleidus (A) in shape and arrangement. 

 They conform closely to the outline of the facets on the humerus, and form a very 

 elegant paddle. The radius (r.) is very large, and its surface is marked in the same 

 fashion as the distal expansion of the humerus. It is shaped like the radius of 

 Cryptocleidus except for its ulnar border, which bears two facets separated by a well- 

 marked foramen similar to that of Tricleidus. Its distal margin bears facets for the 

 radiale (rad.) and intermedium (hit.). The ulna (uln.) is a pentagonal platelet of 

 bone fused to the pisiform (p.), and its radial margin carries two facets separated by 

 the foramen, the other half of which separates the two facets on the radius. It is 

 very similar to the ulna of Tricleidus (A, u.), and articulates in a similar fashion 



