288 EGG-LAVING MAMMALS. 
districts, and subsisting almost exclusively on ants. They are generally found 
in the mountains, and the three-toed species has been taken at an elevation of 
between three and four thousand feet. Although it is definitely ascertained that 
they lay eggs, much less is known of their breeding- 
habits than is the case with the duckbill; according, 
however, to native reports, the young, which are 
probably two in number, are born during the Aus- 
tralian winter, generally in the month of May, 
Remains of a large extinct echidna have been obtained 
from the superficial deposits of New South Wales. 
ALLIED EXTINCT MAMMALS. 

Certain forms from the Secondary and early 
Tertiary rocks of Europe, Africa, and North America 
are believed to belong to the Prototherian subclass, of 
which they probably indicate a distinct order. Their 
molar teeth have a distant resemblance to the teeth 
Saat Sean We RON Reset a oes of the duckbill, while the bones of the shoulder seem 
MAL (3 nat, size), to have comprised the two elements characterising 
the Egg-laying Mammals. The peculiarity in the 
teeth of these mammals is that the molars are traversed by one or two longitudinal 
grooves, on either side of which are ridges carrying a number of small tubercles ; 
and from this feature the name of Multituberculata has been proposed for the 
group. The number of ridges in the upper 
molars is always one more than in those 
of the lower jaw. In some species, as in 
Tritylodon, represented in our first figure, \ 
the premolar teeth are similar to the molars; ; 
but in others, as in our second figure, the 
molars are small, while the premolars are 
large and have sharp cutting edges. When %., 
unworn, such cutting premolar teeth gener- ae ; 
. k LOWER JAW OF PLAGIAULAX (nat. size and 
ally have a series of oblique grooves on the enlarged).—After Marsh. 
sides, and as the incisor teeth (a) are large 
and often reduced to one pair, the jaw resembles that of the rat-kangaroos. The 
molar teeth, however, are different, and if these Secondary Mammals are really 
Prototherians, the character of their teeth indicates that they cannot be the 
ancestral types of the higher groups of the class. 








































