ON A NEW SPECIES OF DICYNODON 137 
plate had a curved inferior margin which ended somewhat abruptly 
anteriorly, corresponding in all probability with the form of the 
middle symphysial ridge in the lower jaw. Superiorly it seems to 
have dilated into a thick bony mass, whose supero-lateral portions 
intervened between the premaxillary and the maxillary bones, while 
its infero-lateral parts extended down on the inner side of the 
maxillary bone, and, as I am inclined from some appearances to 
think, sent back a process along the maxillary wall, close to the 
palatine bones, to form a part of the boundary of the internal 
nares. 
The palatine bones are attached to the presphenoid below the 
anterior boundary of the orbits; they pass, diverging, forwards and 
outwards, till they reach the lower walls of the maxillz, into which 
their upper edges are wedged. Anteriorly, these bones incline in- 
wards and join the lower edge of the ethmovomerine plate. The 
posterior nares are the two spaces enclosed between them, the 
palatine bones, and the ethmovomerine septum. 
The structure which I have just described cannot, I think, be 
explained by the analogy of any recent Reptile, nor am I acquainted 
with any fossil member of the class which presents a similar 
arrangement of the parts. 
In all Lacertilia, Ophidia, Chelonia, and Crocodilia, the palatine 
bone has but a small share in the lateral osseous boundary of the 
posterior nares; while the vomers or vomer often present a broad 
inferior surface, and have little vertical expansion. 
In the Monitors, however, there is a bony mass, commonly called 
the turbinal bone, which appears to me to represent very closely the 
superior expansion of the ethmovomerine plate of Dicynodon. Except 
in proportional size, in fact, it agrees very closely with the latter ; for 
it appears on the upper surface of the skull, between the ascending 
process of the premaxilla, where it is joined by the descending part of 
the nasal, and occupies a broad space between the ascending process 
cf the premaxilla and the maxilla, with whose inner and upper edge 
it articulates. Behind it, the maxilla reaches the prefrontal ; in front, 
the “turbinal” extends inwards to the premaxilla; internally the 
“turbinal” is continuous with a vertical plate which passes inferiorly 
into the vomers; and if these bones, instead of being expanded 
horizontally below, were represented by their thin vertical plate 
only, the resemblance to Décynodon would be close. But the nasal 
passages of Birds present a much nearer approximation to those of 
Dicynodon. In such a bird as a Vulture, for instance, the osseous, 
