CLASSIFICATION OF THE THERIODONTIA. 45 



the whole lateral surface of the brain-case, the structui-e of the 

 zygomatic arches and roof of the skull and occiput with great 

 perfection. It is in many ways the best Gorgonopsid skull 

 known. 



R. 4052. A skull retaining a well-preserved and only slightly 

 sheared snout, with a much crushed posterior part, permitting 

 the definite identification of R. 4053. 



49369. A snout, somewhat distorted and not very well pre- 

 served which has been cut into slabs. It agrees well with the 

 corresponding part of R. 4052. 



All the material of Scymnognathus lohaitsi comes from the 

 JEndothiodou-zone of Beaufort West. T!ie skull, as a whole, is 

 remarkable for the marked distinction between the relatively 

 narrow snout and palate and the wide posfcorbital region. Owing 

 to this shape, the orbits look as much forward as outward. The 

 temporal fossae are very large and face more upwards than out- 

 w\ards. The parietal region is, in consequence, narrow and the 

 occiput deeply cupped, owing to the backward swing of the 

 squamosals from their lanion whh the postorbitals. 



The snout is much more rounded than in Gorgonops or Arctops, 

 although towai'ds the orbits it is still somewhat " square-cut." 

 'IMie external nares closel}^ resemble those of Gorgonops, and there 

 is the same step between the lower edges of the premaxilla and 

 maxilla. 



The structure of the dorsal and lateral surfaces of the skull 

 are obvious from text-figs. 7 & 8, but it is necessary to give some 

 account of the brain-case and palate. 



The basioccipital is fused with the exoccipital and paroccipital, 

 and its suture with the basisphenoid has been destroyed by 

 a fracture. Ifis a long nax-row bone, terminating behind in a 

 single condyle, which is proba bly partly exoccipital. This condyle, 

 as seen in section, is much wider than it is high, the dorsal sur- 

 face being excavated by the lower part of the foramen magnum. 

 The posterior part of the basioccipital is thus thin. 



The exoccipitals are of the ordinary Gorgonopsid or Pelycosaur 

 pattern, but their upper surfaces are concealed by the overlapping 

 elements of the proatlas. Further forward the lower surface of 

 the basioccipital and of the paroccipital fused with it project 

 down as a short, powerful, obscurel}^ bilobed process, whose outer 

 part supports the fenestra ovalis; with this process the powerful 

 tuber basisphenoidalis articulates dorsally, though ventrally the 

 two projections are separated by a gap. 



The paroccipital and pro-otic are fused, not only with each 

 other, but also with the basioccipital ; the suture Ijetween the 

 pro-otic and the basisphenoid remains open. 



The paroccipital process is extremely massive, passing out 

 from the side of the basioccipital on the loAver surface of the skull 

 to its broad abutment on the squamosal. The anterior and lower 

 faces of this process are excavated by a groove which leads inward 

 to the large iri'egular opening, which is the fenestra ovalis. The 



