president's address SECTION D. 115 



the Labyrinthodontia, the latter being probably the ancestors 

 of the former. Messrs Flower and Lydekker say : " We 

 may probably regard the Mammalia as having originated 

 from the same ancestral stock at the time the amphibian 

 type was passing into the reptilian. From this point of view 

 some of the mammalian features found in the more specialised 

 Anomodonts may probably be regarded as having been 

 acquired during a parallel line of development." Whilst 

 much is mere conjecture, we may, I think, best explain the 

 mammalian fauna of Australia by supposing a course of 

 development and distribution somewhat as follows : — 



Far back — certainly in Palaeozoic times — there existed a 

 group of forms of a generalised amphibian type. These we 

 may for convenience term the Architheria. From this 

 ancestral Architherian stock we may imagine the develop- 

 ment of different groups as taking place along lines perhaps 

 at first more or less parallel and then divergent. On tlie one 

 hand arose the amphibian stock and, along lines running at 

 first more or less parallel to this, the primitive sauropsidan 

 forais, whilst one main line of development led to the 

 Prototheria. 



In this group we may suppose that whilst certain features 

 of the earlier forms were retained — such as, notably, the 

 amphibian-like structure of the pectoral girdle and the 

 oviparous habit — there were developed for the first time 

 definite mammalian characters. Of this group the Mono- 

 tremata are the only but much modified survivors. From the 

 Prototheria arose a group of forms which we may call the 

 Archi-polyprotodontia and which may be regarded as 

 having possessed a generalised marsupial structure. The 

 amphibian form of pectoral girdle had been modified, the 

 oviparous habit lost and the viviparous gained, tiiough as yet 

 they were non-placental. From these generalised polyproto- 

 dont forms arose on the one hand the Metatheria, and on 

 the other the Eutheria. 



It seems necessary to postulate the existence of some such 

 group as this before the development of either Eutheria, 

 Multituberculata or Diprotodont marsupials, as otherwise it 

 would be difficult to explain the absence of the two first from 

 Australia, or of the third from Europe, Africa and America. 



We may now attempt to trace the course of events as they 

 appear to have succeeded one another in Australia. 



The first mammalia to reach the region which must of 

 necessity have at one period been connected with South*east 



