92 THE MAMMALIA. 



becoming established. On the other hand, to 

 take a very obvious case, when competent au- 

 thorities emphasize the possibility that birds of 

 the ostrich species (the Ratitae) are of a different 

 reptile origin to the other birds e.g. those with 

 a keel-shaped breast-bone the supposition of a 

 convergence would, in fact, be established ; for bird- 

 like peculiarities are met with in the skeleton of 

 several fossil groups of reptiles, hence the trans- 

 formation to the real bird would in various respects 

 be absolutely no wonder at all. 



The geographical distribution of the Monotrema 

 is confined to South Australia and Tasmania. But 

 a few years ago a new species of Ornithoryncha 

 was described from a perfect skull found in New 

 Guinea. This does not really make the range of 

 their distribution any larger, as New Guinea was 

 clearly at one time connected with the continent of 

 Australia, and consequently belonged to the same 

 zoological province. Not a trace of any fossil 

 discovery leads us from the present living Mono- 

 trema back to the primeval world, to which never- 

 theless they stand in such palpable relation. They 

 are, moreover, widely different from the other 

 groups of living Mammals. Even admitting the 

 debatable supposition that they were directly allied 



