Trof. H. G. Seeley — On Oudenodon from the Cape. 107 



III, — On Oudenodon (^Aulacocephalus) pithecops from the 

 DiCTNODON Beds of East London, Cape Colony. 

 By H. G. Seeley, F.R.S., Professor of Geology, King's College, London. 

 (TIHE genus Oudenodon of A. Gr. Bain, 1856, was adopted by Sir 

 JL Richard Owen, and defined as comprising Anomodont reptiles 

 of the type of Dicynodon, but absolutely toothless. Still, they were 

 referred to a family Cryptodontia, under the belief that the 

 teeth were immature and had their development arrested, so that 

 they never descended to the adveolar margin. A transition might 

 easily be made from the caniniform production upward of the 

 alveolar border seen in Oudenodon to the small teeth in Dicynodon 

 dubius and J), recurvidens, which are in contrast to the great lateral 

 ridges formed by the roots of the teeth in most species of the genus. 

 The species strigiceps was referred first to Dicynodon and then 

 to Oudenodon. Owen described eight species, which differ from each 

 other in the elongation of the head, in the form of the preorbital region 

 and its prolongation in front of the nares, in the forms of the orbits of 

 the eyes, and the anterior nares, and in the median postorbital region 

 beiug either a sharp ridge or a more or less flattened concave 

 channel. These chai'acters might have been used to define genera. 



The species fall, more or less easily, into two groups, and this is 

 also true for Dicynodon. The same chai'acters difi'erentiate the 

 short-nosed from the long-nosed species of both types, suggesting 

 that the genera based on presence ov absence of teeth in this case 

 are artificial. Thus, the short-nosed Oudenodons are almost in- 

 distinguishable except as species from the short-nosed Dicynodons ; 

 and the long-nosed Oudenodons similarly approximate in skull-shape 

 to the long-nosed forms of Dicynodon. 



I therefore propose to divide Oudenodon into two subgenera. 



The short-nosed types, with a wide flattened concave region 

 between the temporal vacuities, the parietal foramen in its middle 

 length, and orbits more or less circular and directed forward and 

 upward, are represented by the species O. Baini, 0. raniceps, and 

 0. megalops. They may be indicated by the name Aulacooephalus. 



The prognathous species have the orbits more lateral, the parietal 

 foramen just behind the orbits, and a sharp median ridge between 

 the temporal vacuities which may extend along their length or be 

 limited to a part of it. This group is represented by the species 

 0. magnus, 0. prognathus, 0. brevirostris, and 0. Greyi, and may 

 be indicated by the name Khachiocephalus. 



In the same way I would divide Dicynodon into two subgenera. 



The short-nosed species have a broad concave parietal interspace 

 between the outwardly inclined faces of the postfrontal bones, 

 which make the inner borders of the temporal vacuities. The 

 parietal foramen is in the middle of this area. The nares are 

 scarcely seen when the skull is viewed from above, and owing to the 

 shortening of the snout the orbits are directed forward. The species 

 include -D. Baini, D. tigriceps, and presumably D. testudiceps, and 

 may be defined by the name Aulacephalodon. 



