56 



Measurements. 



M. 



Antero-posterior diameter of specimen ■ 250 



Greatest transverse diameter - • 210 



Height of centre of upper surface above the level '125 



Width of interpterygoid vacuities about • 040 



Maximum thickness of cranial armature about '016 



"With the head, just described, were five keeled, bony scutes or plates that have since 

 been found to fit together in the form of an arch (plate XII, figs. 3 and 4), whose sides 

 curve forward as well as downward. This oblique curve places the lower, paired scutes, 

 as seen when the arch is viewed from above, a little in advance of the upper pair which 

 is again slightly in advance of the median plate 



The scutes rest on and are ossified to a thickness of bone that constitutes the inner, 

 continuous surface of the arch. This band of bone, ornamented above by paired ossicles, 

 suggests the possibility of its being the back border of the posterior crest of the species 

 to which the head armature, above mentioned, belonged. 



This suggestion is given credence from the fact that the concave edge of the band of 

 bone on which the scutes rest is fractured, whilst the convex edge appears to be intact. 



Numbering the ossicles from the right, the junction between Nos. 1 and 2 was per- 

 fect, as were also those between Nos. 3, 4 and 5, but in the case of Nos. 2 and 3 the frac- 

 tured edges did not fit with sufficient exactness to remove all doubt as to their being 

 placed side by side, although the continuity and symmetry of the curve of the under 

 surface seemed complete. It is possible that one or two scutes are missing from between 

 Nos. 2 and 3, especially as fragments of similarly shaped scutes were found at the same 

 spot. If an additional scute completed the series it probably would have been the mate 

 of the present median one, or if two were required to fill the gap (if such a gap exists) 

 one would be on the median line, the other would correspond with No. 3 to form another 

 pair. The addition of one or two scutes to the series would result only in extending 

 and possibly flattening the curve. 



The median scute is apparently symmetrical, the others are asymmetrical, forming- 

 pairs with reversed lateral proportions. 



The scutes have an irregularly oval basal outline, are sharply keeled, with sloping 

 sides shallowly excavated from the keel downward but convexly curved from front to 

 back, their basal edges are defined by an engirdling furro'v^' below which, at a lower 

 level, they are latei'ally expanded to meet each other in a plane surface. A very small 

 ossicle rises above this intermediate basal surface between Nos. 3 and 4. Vascular 

 markings are conspicuous on the sides of the scutes. 



From the appearance of the outer, basal edges of scutes Nos. 1 and 5, it seems prob- 

 able that these scutes constituted the lateral terminations of the series. 



