ON A NEW SPECIES OF DICYNODON 135 
hardly have been less than 24 inches; and, in the coronary region, 
the ramus attains about 2 inches in this direction. 
The skull whose external characters have just been described is 
distinguished from those of all hitherto discovered Dicynodons by— 
1. The great angle formed by the planes of the intertemporal and 
facial regions of the upper surface of the skull. 
2. The excess of the transverse over the longitudinal diameter of 
the supratemporal fossz. 
3. The position of the nasal aperture altogether in front of the 
orbits. 
4. The proportional length of the upper jaw in front of the nasal 
apertures. 
5. The length and form of the os quadratum. 
6. The circular section and straightness of the tusks ;! the position 
of their posterior ends immediately below the nasal apertures ; their 
extension downwards and forwards parallel with the plane of the 
nasal and premaxillary bones; and their not leaving their sockets 
till they have passed beyond the level of the posterior end of the 
symphysis of the mandible. 
7. The longitudinal ridges on the prism-like snout. 
The Structure of the Skull of Dicynodonts—The general structure 
of the Dicynodont skull, so far as it is visible from the exterior, and 
without making sections, has been fully elucidated by Professor Owen 
in his papers in the Transactions of this Society (vol. vii.); but no 
attempt has been made hitherto, so far as I am aware, to work out 
the anatomy of its deeper-seated parts. 
The remarks I am about to offer are the results of my observa- 
tions upon Decynodon Murray?, and upon a small skull from the 
Rhenosterberg, the species of which is not determinable with 
certainty. 
The cranio-facial axis is more completely ossified in Dzcynodon 
than in any Reptile I am acquainted with, the presphenoid, the ethmoid 
and the vomer being, so far as I can observe, entirely osseous. 
The basi-occipital is extremely short, and the basi-sphenoid is a 
very strong cuboidal bone, whose posterior face projects freely, for 
half its extent, below the basi-occipital. This portion of the bone 
slopes downwards as well as backwards, and is concave from side 
1 Where the tusks are other than circular in section, their figure is clearly distorted by 
pressure. It is a curious circumstance, indeed, that no one of the skulls of Décynodon 
Murrayt which I have seen is free from a certain amount of disfigurement from this 
cause. 
