MULTITUBERCULATA. 285 
as shown in the accompanying cut, are of relatively large size, 
and are characterised, when unworn, by having a highly com- 
pressed, convex crown, with its summit narrowed toa sharp 
cutting edge, and its sides usually marked by oblique ridges 
and grooves. ‘The single pair of lower incisor teeth are curved 
and pointed. 
It was from the resemblance of their remarkable premolar 
teeth to the last premolar tooth of the Rat-Kangaroos, coupled 
with the presence in both groups of a single pair of large 
lower incisors, that led to the Multituberculata being included 
among the Diprotedont Marsupials. An important point of 
One half of an imperfect Lower Jaw of a North American Representa- 
tive of the /Vagiaulacide. Much enlarged. (After Marsh.) 
difference between the two groups is, however, to be found in 
the circumstance that whereas in the Rat-Kangaroo the summit 
of the crown of the last premolar is slightly concave, in all the 
Piagiaulacide it is markedly convex. 
It is noteworthy that the earlier members of the family have 
a large number of premolars, and but few grooves on the last 
tooth of that series, whereas in the later forms the number of 
premolars diminishes, while the grooves on the last premolar 
becorme more numerous. 
The nature of the food of Plagtaulax, all the species of 
