298 ORDERS OF MAMMALIA. 



very remarkable type of the Marsupials ; and it must have 

 attained a very great size, since the length of the crown of 

 the great pmemolar is not less than two inches and a quarter. 



Just as the living Kangaroos and AVombats of the Aus- 

 tralian province find Post-Tertiary representatives within the 

 same geographical region, so also do we find that the Poly- 

 protodont Marsupials existed side by side with the preced- 

 ing. Moreover, the Post-Tertiary Polyprotodonts belong to 

 types which still exist in Australia, and which are peculiar 

 to it. Thus the living Bandicoots {Peramdes) have their 

 Post-Tertiary representatives ; and the more highly carni- 

 vorous and predatory Thylcici7ius and Dasyurus of Van Die- 

 men's Land were preceded by closely allied forms, which 

 ranged over the mainland of Australia. 



Precisely parallel phenomena are observable in Xorth and 

 South America, all the living Marsupials of which belong to 

 the Polyprotodont family of the Opossums {Didelphidm). 

 Apart from the early appearance of this Marsupial type in 

 the previously-mentioned 'Dryolestcs of the North American 

 Jurassic, the Post-Pliocene deposits of tlie same continent 

 liave yielded bones actually referable to the living genus 

 DidclpUys. In South America, also, the Post-Pliocene cave- 

 deposits of Brazil have yielded various species of the same 

 genus. These examples, then, afford a very striking illustra- 

 tion of the general law that tlie Post-Tertiary Mammals of 

 a given country belong in a general way to types of structure 

 represented in the same region at the present day by forms 

 often generically different. 



