106 
FOSSIL JAWS OF MACBOPODIDjE, 
from 33-1 to 39-9 (5); of the first two from 21-5 to 27-4 (7); of 
m. 2 , m. 3 from 28-0 to 34-1 (11); of m. 2 17 (1); of m. 3 from 17-0 
to 18-4 (6); and of m. 4 16-6 (1). The breadth of the palate is 
from 66-0 to 68-5 (2). 
In young: p. 3 , mp. 4 , m. 1 range from 28*6 to 37'0 (3); mp. 4 , 
m. 1 , m. 2 41-7 to 44'4. 
The proportionate mean widths of m. 3 above and below are 
11-8 and 13-6. 
The degree of variation in the length of the cheek-teeth found 
in this species is less than that shown by H. ruficollis; and the 
premolar has a more restricted range of length than in most of 
the larger existing wallabies. On the other hand, the width of 
the teeth and the depth of the mandible have a somewhat greater 
range of measurement than in living species, and in thickness the 
ramus is decidedly more variable. But as in all the dimensions, 
the extremes are reached by insensible gradations, excess even in 
the width of the teeth must be considered a peculiarity of the 
species and one probably related to its inordinate vigour as shewn 
in its fecundity. It is quite the most abundant Macropod of its 
period. 
As no one of the several species added by Owen to the type of 
his genus ProtemnoJon has a destinctive character other than a 
supposed differentiation in size, Lydekker has taken a step in the 
right direction in reducing their number to three — brehus, rcechus 
and anak. With a fuller supply of material he would no doubt 
have felt perfectly safe in referring all the fossils of the Protem- 
nodont series to the single species anak. The essential unity of 
the species is shown not merely by graduation of difference affect- 
ing each part of each of three hundred and thirty individuals 
alike, but by that disproportionate difference between the parts 
which renders it impossible to lay down interspecific lines of 
demarcation anywhere. Detailed measurements of thirty-four 
entire mandibles of brehus, rcechus and anak, and a careful com- 
parison of their differences with those observed in the measurement 
of recent species fail to show that there is any sufficient reason 
for regarding them as distinct species. Constant differences of 
form there are none. 
