88 



ON THE CLASSIFICATION, OF THE THERIODONTIA. 



natural one, the conservative main stem which leads on to the 

 Cynognathids being represented by a series of Gorgonopsids of 

 which Gorgonops itself is one of the most primitive members. 

 From this stem side-branches arise, which retain the broad 

 parietal region and other primitive features, but present either 

 an accelerated development of certain regions or are indi- 

 vidually specialised. From still earlier members of the main 

 stem arose the groups of animals, resembling one another in 

 the precocious conversion of the broad intertemporal region into 

 a sagittal crest and in the acquirement of suborbital vacuities, 

 which are usually included in the Therocephalia and belong to 

 many independent stirps, each in all probability being dependent 

 on the mam Gorgonopsid stock. It is shown that there is a 

 series of evolutionary trends which persist throughout the whole 

 group of Anomodonts from Varanosaurus to Diade?nodon, and 

 that the special rapid advances which separate the Therocephalia 

 from the Gorgonopsids, in the main, merely follow out the pre- 

 determined evolutionary track proper to the group. 



Thus any classification of the Therioclontia is necessarily 

 complicated, as involved and difficult of construction as that of 

 the Theria themselves. Existing material is so incomplete that 

 any attempt at detailed classification, even if only into families, 

 is dangerous, in that it will load the literature with undefined 

 groups, whose characteristic forms may only be known from the 

 front end of the skull or the dentition. 



The detailed descriptions of skidl-structures in this paper show 

 how unreliable, even for generic distinction, are the characters 

 presented by the teeth of Theriodonts. 



Thus, for the present, I am inclined to retain my former 

 division of Therioclontia into Gorgon op si dse, Therocephalida?, 

 Cynognathida?, and Bauromorpha, fully recognising that these 

 groups — or, at any rate, the first two — cover a multitude of forms 

 not directly of common origin and only held together by two 

 or three striking characters. 



It remains to discuss the connections of the Theriodontia 

 with the other groups of South African Anomodonts — the 

 Deinocephalia, Dromosauria, and Dicynodonts. 



In the copper-bearing sandstones and associated limestones of 

 the Ural Mountains, which immediately succeed the Artinsk 

 beds and are shown by a comparison of reptile and amphibian 

 faunas to be slightly older than the Tapinocephalus- zone, are 

 found three types of Anomodonts, each represented by skulls or 

 jaws: of these Deuterosaurus is clearly a Deinocephalian of the 

 Tapinocephaloid group recalling man} 7 South African forms. 



Deinosaurus ( = Cliorhizodon) is represented by jaws, in one 

 case associated with a palate whose dorsal surface is well exposed. 



Rhopalodon is a name covering not only several jaw-fragments 

 but also a complete skull, which was described by Prof. Seeley. 



Of this skull, remarkably beautiful lithographic drawings of the 



