XIII 



PHYLUM CHORDATA 



601 



rbynchus come nearer in pattern to those of certain of the 

 Multituberculata than to those of any other known group is looked 

 upon as evidence that the affinities of the latter are rather with the 

 Prototheria than with the Metatheria. In the American 



FIG. l_'_'7. Phascolotherium bucklandi. Inner view of right ramus of mandible. (After 



Owen.) 



Cretaceous beds in which these teeth are most abundant a number 

 of limb-bones have also been found, some of which show evidence of 

 Monotreme characteristics. 



Fossil remains of Mammals belonging to the Cretaceous age are 

 known only from certain limited beds in North America. But 

 in deposits of the succeeding Tertiary period there have been 

 found the remains of an extensive and varied Mammalian fauna. 

 The earlier Tertiary Mammals in many cases present features which 



..-i 



FKI. 1-Ji'S. Plagiaulax becklesi. Mandible with teeth. (After Owen.) 



enable us without hesitation lo refer them to one or other of the 

 existing orders ; but when this is the case there is nearly always to 

 be recognised an absence, or a less advanced development, of some 

 of the more salient characteristics ; in other words, the earlier 

 Tertiary Mammals, when referable to existing orders, are less 

 highly specialised than the living representatives of these orders. 

 No less significant is the fact that these early Tertiary representa- 



