BY C. W. DE VIS, M.A. 183 
Of the bones of the skull, with which the present communica- 
tion mainly deals, the latest and most useful acquisition is that 
which forms the subject of Plate X., Fig. 1. 
THE ANTERIOR HALF OF A YOUNG LOWER JAW. 
The salient feature of this fossil isits predominant breadth at 
the symphysis, the length of which is considerably less than the 
space between the inner edges of the sockets of the canines. 
In the fresh water species named by its first examiner Croco- 
dilus johnstoni, and subsequently referred to several other 
genera, the symphysial length is more than twice the distance 
between the outer edges of the same sockets; it is nearly equal 
to that same distance in the young C. porosus, but in the adult 
jaw of the littoral species it is relatively shortened by the 
lateral expansion attendant upon the dilatation of the maxil- 
laries during growth: yet even here it is equal to the distance 
from the outer edge of one alveolus to the middle of its fellow 
of the opposite side. 
In the fresh water johnstoni, the width of the ‘watdibie at 
the fourth tooth equals its length from the tip to the hinder 
edge of the third socket; in the young C. porosus, to that of the 
fourth, and in the adult of the same species to that of the fifth 
socket. In the fossil it extends backwards to the centre of the 
seventh. 
The symphysis in the living species of the tablelands, john- 
stom, ends opposite to the hinder edge of the sixth socket—in 
the salt water reptile, old and young, opposite to the end of the 
fifth. In the fossil it attains the level of the posterior third of 
the fifth alveolus, but at the same time exemplifies the 
vagueness of this mode of indicating the proportions of the 
symphysial region; the more rounded muzzle of the fossil species 
is absolutely much shorter, though relatively to the dental 
series but little shorter, than the comparatively pointed chin of 
the adult C. porosus. Keeping in view the immaturity of the 
present subject, it may be said to exhibit a shorter and more 
