114 president's address — SECTION D. 



Thomas we owe a fuller understanding of their nature and 

 relationships. 



We may, apart from the Eutheria, divide Australian 

 mammals into three main groups, — (1) Monotremuta, (2) 

 Polyprotodont marsupialia, and (3) Diprotodont marsupialia. 



In Europe, America and Africa we have evidence of the 

 existence, either now or previously, of two groups, — (1) a 

 series of forms, all fossil, grouped together as the Multituher- 

 culata ; (2) Polyprotodont marsupialia, — all extinct except 

 the single American family Didelphyidae. That is, the 

 Monotremata and Diprotodont marsupialia are confined to 

 the Australian region, the Multituberculata are not found 

 in it, whilst the Polyprotodont marsupialia are common to 

 it and other regions. 



The Multituberculata and Monotremata are by some 

 authors placed together in the Prototheria mainly on account 

 of a general resemblance between the tuberculate teeth of 

 these forms and the Monotremes. The former possess a 

 single pair of lower incisors as do the diprotodonts ; but it is 

 the second and not the first upper incisor which becomes 

 enlarged and opposed to the incisor of the low jaw. The 

 secant fourth premolar also differs in shape in the two and in 

 face of these differences and the absence of knowledge as to 

 other important parts of the skeleton, such as the pectoral 

 girdle, all that can, perhaps, safely be said is, (1) they cannot 

 be classed with the Diprotodontia and (2) they form a group 

 not represented in Australia, but once widely spread over 

 Europe, America, and Africa. 



Both Multituberculata and Diprotodontia may be regarded 

 as modifications of an original polyprotodont type, which, 

 there can be little doubt, was much more primitive than 

 either of the two former and closely resembled what we may 

 consider as the ancestral form of all Metatheria. 



The relation of this ancestral form to existing monotremes 

 is a matter of conjecture ; but the latter appear to retain 

 characters common to themselves and to groups more 

 primitive than the marsupials, or probably also than the 

 immediate polyprotodont ancestors of the latter. Such 

 characters are, for example, the structure of the pectoral 

 girdle and the oviparous habit. 



Professor Cope came to the conclusion that the extinct 

 reptihan forms — the Anomodontia — were to be regarded as 

 the ancestors of Mammalia. Subsequent research has shown 

 a close relationship to exist between the Anomodontia and 



