436 J. W. HTJLKE ON IGUANODON PEESTWICHII 



the parietal by sutura harmonia. In their present mutilated state 

 the back and sides of the skull form a rude pyramid, of which the 

 base of the posterior face is notched by the foramen magnum, 

 and the postero-external angle is formed by the truncated sus- 

 pensorium. 



The lower borders of the fragment correspond to the upper 

 borders of the basis cranii. They, as also the inner surface, are too 

 mutilated for description. 



On the under surface of the base of the right suspensorium is a 

 wide groove, directed forwards and inwards. It exactly corresponds 

 to the groove in the Brooke skuU to which I lately referred, and 

 may have lodged the stapedial rod. 



PL XYIII. figs. 1, 2. A third fragment of the skull (No. I. 10) 

 comprises parts of the parietal and frontal regions and of the left 

 temporal bar. The parietal bone is single ; no trace of mesial suture 

 joining two halves is discernible. This is mentioned ; because in the 

 nearly allied Hypsilophodon such a suture has been thought to exist. 

 The sides of the parietal fall off steeply from a sharp median crest, 

 which divides in front, and, bending outwards, here forms the an- 

 terior boundary of the upper temporal opening. There is no parietal 

 foramen. 



The frontal is a very large bone. Its length contrasts strongly 

 with the shortness of the parietal; and its breadth also is con- 

 siderable. It consists of two halves, united by a very evident 

 mesial suture. Its structure is very dense, without diploe. Deep 

 sutural indentations in its right border show that the prae- and 

 postf rental bonfes approached each other very closely, and that the 

 frontal formed but a small part, if any, of the upper border of the 

 orbital opening. The direction of this Jopening is lateral, as in 

 Hypsilojphodon Foxii. The postfrontal bone, of which part is pre- 

 served on the left side, is large ; its smooth orbital surface is of 

 great extent ; a long slender branch separated the orbital from the 

 lateral opening ; and a stronger branch directed backwards forms the 

 anterior part of an upper temporal bar. 



In the undersurface of the fossil are shown : — 1st. A large lozenge- 

 shaped mesial hollow — the vaulted inner surface of the skull — 

 narrow behind, in its longer diameter sinuous, being convex in the 

 parietal part and concave in the frontal. Its greatest width coin- 

 cides with the parieto-frontal suture. It narrows anteriorly at a 

 line drawn through the middle of the orbital surfaces ; and in front 

 of this it expands for the reception of the olfactory lobes, which 

 must have been of large size — an inference confirmed by the large 

 size of the nasal chambers, indicated by the great size of the nasal 

 bones. 2nd. Laterally, on each side of: the vault of the skull- 

 chamber is the smooth orbital surface lately, mentioned. Its out- 

 line is roughly rhomboidal. The two outer sides are sutural, as 

 already mentioned, and afi'orded attachment to the prse- and post- 

 frontal bones. The inner angle is rounded oft", and the two inner 

 sides make a continuous curve. Of this the posterior f are broad and 

 rough as if sutural, and the anterior | is a thi.n,;smaoth, free crest. 



