136 ON A NEW SPECIES OF DICYNODON 
to side. The inferior face, wide but short, is also concave from 
side to side, but is a little convex from before backwards. The 
pterygoids abut against the lateral and inferior parts of the basi- 
sphenoid. 
The presphenoid is united with the basisphenoid by an oblique 
sutural face: posteriorly it is thick and solid; but anteriorly it thins 
off into a vertical plate, which extends continuously between the 
orbits and forms a bony interorbital septum. 
The interorbital septum passes into the ethmovomerine plate or 
nasal septum, which, as far forwards as the front part of the external 
nasal apertures, is an exceedingly thin but deep plate of bone (fg. 3, 
Pl. XXII. [Plate 8]), At the anterior boundary of this aperture, 
however, the upper portion of the nasal septum thickens and rapidly 
expands into a broad and thick spongy mass, consisting of a hori- 
zontal and a vertical portion. The former is 1} inch wide. Its flat 
summit articulates with the ascending process of the premaxillary 
bone; while its obliquely truncated lateral faces, half an inch wide, 
appear on the face, between the supero-lateral and median-lateral 
ridges, being interposed between the premanillary and the maxillary 
bones, which are completely separated by this horizontal prolongation 
of the septum narium. The inferior sides of the mass slope down- 
wards and inwards to join the vertical portion of the thickening, 
which is 33,ths of an inch long, by ;%jths wide. Its sides are convex, 
its inferior surface is concave, and from its centre proceeds the thin 
bony plate which constitutes the proper nasal septum. The maxillary 
bone unites suturally with the inferior face of the horizontal portion 
of the bony expansion, and with about the upper half of the outer 
surface of the vertical portion (Pl. XXII. [Plate 8] fig. 4). 
In a section taken nearly an inch further forwards (Pl. XXII. 
{Plate 8] figs. § and 6) the bony expansion has enlarged and 
acquired a quadrate form, the vertical portion having expanded, so 
as to be nearly as wide as the horizontal, and uniting throughout the 
whole of its outer surface with the maxillary bone. Its lateral 
portions have extended downwards below the level of the alveoli, 
while the centre of its inferior surface has hardly altered its distance 
from the anterior, or superior, boundary of the snout. In consequence 
of this, the inferior surface of the spongy mass forms a deep arch, 
from whose centre depends the proper nasal or vomerine septum, 
which has attained a thickness of }th of an inch. 
An inch further towards the end of the snout, no trace of these 
parts is seen in a transverse section; and I conclude, partly from 
these sections and partly from other evidence, that the ethmovomerine 
