DICYXODONTID^. 37 



parietal have come into contact. The deep depression in 

 the supraoccipital above the foramen magnum is well 

 shown ; and the left quadrate is in position. 



Purchased from T. Bain, Esq., 1880. 



R. 866. The crushed occipital portion of a nearly similar cranium, 

 {Fig.) with the anterior cervical vertebrae ; from the Gouph 

 district. Figured by Seeley, op. cit. pi. xii., as Dicynodon 

 (Tropidostoma) dunni, of which it is the type. The two 

 sides of the occiput have been crushed in towards the 

 middle line. The right quadrate is entire. The cervical 

 ribs articulate by one head to a process on the arch and by 

 another on the centrum of the vertebrae. This specimen 

 has received a lateral crush, so that the squamosals are 

 approximated to one another and deflected backwards; 

 " the root of the temporal arcade is likewise thrust towards 

 the parietal bar. Making allowance for this difference, 

 the specimen apparently presents no characters by which 

 it can be specifically distinguished from the preceding. 



Purchased from T. Bain, Esq. 



Ptychosiagum murrayi (Huxley *). 



Syn. Dicynodon murrayi, Huxley 2 . 

 Ptychognathus verticalis, Owen 3 . 

 Piychognathus boopis, Owen 4 . 

 Dicynodon copei, Seeley 5 . 



Cranium with the occipital and fronto-parietal planes forming a 

 largely obtuse angle with one another, and the fronto-parietal and 

 premaxillary planes a slightly obtuse one; fronto-parietal region 

 convex antero -posteriorly, and thus tending to form a gradual 

 passage from the occipital to the naso-premaxillary plane. Attains 

 dimensions equal to the preceding species. 



The differences between the specimens to which the above names 

 have been applied appear to be solely due to age or to distortion 

 by pressure and crushing. If such points of difference be regarded 

 as specific, nearly every specimen will form the type of a species. 



It is not improbable that Ptychognathus depressus, Fischer 6 , is 

 based upon a much flattened skull of this species. 



1 Quart. Journ. Geol. Soc. vol. xv. pp. 555 and 649 (1859). — Dicynodon. 



2 Loc. cit. 3 Ibid. vol. xvi. p. 54 (1860). 



4 Cat. Foss. Kept. S. Africa, p. 50 (1876). 



5 Phil. Trans, for 1889, p. 241. 



6 Nouv. Arch, clu Museum, ser. 1, vol. vi. p. 179, pi. x. (1870). 



