Arrangement of the Fossil Kanqaroos. 207 
J g 
classification cannot be attempted; and it is much to be re- 
gretted that the author had so little material at his command 
at the time. Since the work was published, Professor Owen 
has received numerous additional proofs, through his chief 
contributor and friend, Dr. George Bennett, and amongst these 
at least a dozen fragments of skulls, with the incisors perfect 
or nearly so. The grinding-series differs much in some groups ; 
and seldom can a pair of skulls be found which have the teeth 
alike. The grinders are always subject to more than the usual 
variation ; and for this purpose large quantities of skulls were 
brought together and examined here before classification was 
attempted. The result led to the conclusion that by the upper 
front teeth only (of half-grown or almost adult individuals) 
can skulls be named with certaity. There are two kinds of 
third upper incisors which occur with premolars of a certain 
form ; and this sanctions the division into two large groups as 
above, with the following additional characteristics. 
1. Macropus. 
With a broad third upper cutting-tooth (without a fold or 
groove when adult), with deciduous premolars, and subject to 
shedding the grinders up to a single pair in each ramus in 
old age. 
2. HALMATURUS. 
With rather narrow and grooved third upper incisors and a 
more permanent dentition, the grinders being worn down but 
seldom shed. Besides this distinguishing point, the distance 
between the lower incisor and the premolar must be considered ; 
and the wider this space, the sooner the teeth are reduced in 
number; the shorter, the longer are the grinders retained. 
Compare this space in a wallaby’s jaw with that of a kan- 
garoo, and the difference will be understood at once. A long- 
headed kangaroo sheds the grinders, whilst a short-headed 
wallaby wears them out. 
To illustrate this it is necessary to refer to the author’s 
splendid illustrations. On plate xx. we have a long-headed 
kangaroo (under fig. 1), certainly with a short wpper third in- 
cisor, but with every indication that the grinders will be shed 
with age and not worn down. Figures 13 and 15 represent 
similar animals, who shed their teeth; but No. 11 (a rock- 
wallaby’s lower jaw) belongs to the “ grinding-down ”’ section, 
and in this the space between incisors and molars is very short. 
On plate xxiv. (figures 10, 11, and 12) the lower den- 
tition of our black wallaby is given. The wear of the incisor 
below, and the corresponding teeth above, shows that the 
animal was fully adult, but had not shed the premolar, as true 
