366 BRITISH FOSSIL REPTILES. 



Jaw of the Hi/laosaurm ? (PL 39, figs. 1 — 5). 



No. ^«^, 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 1 inch 5 lines 

 deep at the fore part ; flattened and smooth at the inner side (PI. 39, 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 ; tbe 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 ; 

 and at the part where the inner wall has been least mutilated, it nearly completes the 

 socket, and incloses the long and slender fang of the tooth. Whence, I conclude, 

 that the entire jaw of the extinct reptile would have exhibited a series of true sockets, 

 with obhque outlets, not depressions merely, as in the present mutilated fragment ; 

 and that it would have agreed with the Megalosaurus in presenting the sub-thecodont 

 mode of implantation of the teeth. 



The crowns of all the teeth are broken off ; the small sockets of reserve, exposed 

 at the inner side of the base of the old sockets, do not contain any evidence of the 

 species to which this fossil has belonged. 



