1460 



EGG-LAYING MAMMALS, OR MONOTREMES 



generally white, and the color of the fur is dark brown or black, although the head 

 may be almost white. 



Echidnas are fossorial and mainly nocturnal animals frequenting rocky 

 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 

 UNDER PART OK THE SKULL OF A molar teet h have a distant resemblance to the teeth 



SOUTH-AFRICAN SECONDARY r , j 1 1-11 \ -1 *t- u r it. t. 1 J 



of the duckbill, while the bones of the shoulder seem 



MAMMAL. 



(Two-thirds natural size ) * have comprised the two elements characterizing 



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 Multittiberculata 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- 

 ally have a series of oblique grooves on the 

 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. 



LOWER JAW OF PLAGIAULAX. 



(Natural size and enlarged.) 



(After Marsh.) 



