CLASSIFICATION OF THE TUERIODONTIA. 



37 



Arctops has a depressed and very massive skull, the snout, 

 when broken off about 5 cm. in advance of the orbit, being 

 rectilinear in section, bounded by a straight dorsal surface which 

 passes somewhat abruptly into straight, nearly vertical, lateral 

 surfaces. The orbit is small, placed high in the skull, and nearly 

 laterally directed ; its upper margin is continued forward by a 

 ridge separating the dorsal surface from the lachrymal region, 

 which is excavated into a shallow depression. The interorbital 

 region is very wide, forming a flat surface bounded laterally by 

 shallow bays over the orbits. 



Text-fioure 1. 



B.Oc Ex.0c Au.Gr. 



Arctojis willistoni Watson. Type-skull. 



Dorsal aspect. Xf . 



B.Oc, basioccipital ; I. Par., interparietal ; Sq., squamosal ; Tab., tabular 



The parietal region, also flat, is even wider than the interorbital 

 surface ; it separates the very small temporal fossa? which face 

 more largely laterally than dorsally. The occipital surface is 

 very wide and is separated from the parietal by a sharp corner. 

 The squamosal is small, consisting mainly of a vertically standing 

 plate passing directly outward from the end of the massive 

 paroccipital process. The posterior surface of the bone at this 

 articulation is produced backwards into a ridge which forms the 



