38 



MR. D. M. S. WATSON ON THE 



inner wall of the auditory groove. Sutures over the outer 

 surface are not clearly recognisable. 



I have already described the basicranial region, but would 

 again call attention to the flat, laterally directed, plate-like basi- 

 pterygoid processes. The narrow ridged girder formed by the 

 parasphenoid and pterygoids extends forward to the front of the 

 orbit, where it suddenly passes into the wide posterior end of the 

 palate. The pterygoids pass outward to form thick downwardly 

 directed flanges, not very deep when compared with later forms, 

 but of great antero-posterior extent. The middle region of the 

 posterior part of the palate forms a slightly raised area separating 

 two concavities, whose surface lies mainly on the ectopterygoids, 

 large square bones which only take a small part in the great 

 flanges. The middle part of the palate forms a shallow groove 



Text-fieure 2. 



Au.Gr 



Arctops willistoni Watson. Type-skull. 

 Right lateral aspect. Xf. 



B.Sp., basisplienoid ; Pt., pterygoid. 



beginning at the extreme posterior end and running forwards to 

 the posterior nares. At about the level of the anterior end of 

 the ectopterygoicl, this groove is overhung by a pair of small 

 processes rising from the pterygoids. Further forward the floor 

 of this groove is cut into by the narrow slits which represent the 

 posterior ends of the posterior nares. These are separated by 

 a narrow bar of considerable vertical depth. The structure of 

 this bar is not quite certainly determinable, but on the curved 

 fracture which forms its present front termination it is certain 

 that its upper surface consists of a pair of ridges separated 

 by a parallel-sided cleft not more than a millimetre wide and 

 nearly a centimetre deep. Prom this slit a suture seems to be 

 continued on to the palate. Further back two lateral ridges are 



