WEALDEN FORMATIONS. 19 



margin sharp, but not produced at the middle of the bone, as in the Iguanodon : 

 the distal articular surface is convex at its anterior half, trochlear at its posterior half, 

 or with a median, rather oblique groove between two tuberosities. 



The middle metapodial (m) differs from that of the Iguanodon in its uniformly 

 almost flat anterior surface. The outer metapodial (figs. 1 and 3, it) has a flatter 

 and relatively broader outer surface than in the Iguanodon : the antero-internal border 

 subsides about half way down the shaft : the internal border appears to be produced 

 towards the middle metapodial, as in the Iguanodon. The distal end of the outer meta- 

 podial ( iv) must have extended lower than that of the inner one. 



The size and texture of the above-described bones of the foot accord best with the 

 characters of the osseous texture in the Hykeosaurus, of which they are probably part 

 of the hind-foot. 



Jaw of the Hylczosaurus? (T. VIII, figs. 1 — 5). 



No. a 4 ^, in the Reptilian Series of the British Museum, is a portion of the right 

 ramus of the lower jaw, with characters distinguishing it from that of any other known 

 Saurian : as, for example, its curvature, indicating the lower jaw to have been bent 

 down in an unusual degree, and the remarkable inequality of its external surface. This 

 fragment is about 3 inches long, 1 inch 7 lines deep at the hind part, and I inch 5 lines 

 deep at the fore part ; flattened and smooth at the inner side (T. VIII, fig. 2), but 

 having the outer side (fig. 1) raised by the termination of a strong angular ridge at its 

 lower and hinder part, and by a rough convex longitudinal ridge extending along its 

 upper part ; the surface of the jaw being concave above and below this ridge. The 

 lower margin is thick and convex ; the upper one (fig. 3) is formed by a regular series 

 of pretty close-set sockets, with the internal alveolar wall imperfectly developed, and 

 in part broken away, displaying their partitions ; but with the outer wall entire, thin, 

 and slightly crenate at its upper margin (fig. 1). 



At the hind part of this fragment (fig. 4) the anterior extremity of the splenial 

 piece is preserved ; the rest is formed exclusively by the dentary piece : the area of 

 the wide conical cavity in the interior of the jaw is exposed at the back part of the 

 fragment; its apical termination is near the fore part (fig. 5). A succession of large 

 vascular canals open obliquely forwards in the concavity above the upper oblique 

 longitudinal ridge. The whole of the outer surface is minutely ridged and punctate. 



The depth of the sockets bears a smaller proportion to that of the jaw than in modern 

 Lacertians or Crocodiles, being about one fourth of that depth (fig. 2) ; the partitions 

 of the sockets, which are very regular in their breadth and depth, though they are 

 more prominent than in the pleurodont Lizards, yet exhibit a fractured margin ; there 

 is no trace of a smooth natural surface of the bone in the interspace of the sockets ; 



