ISO THE ARCTOG^EIC REALM. [CHAP. 



marsupials and multituberculates is met with in rocks of Cretaceous 

 age ; and it is most probable that if suitable freshwater beds were 



FIG. 29. UPPER SURFACE OF SKULL OF Tritylodon. Somewhat reduced. 



extant, the same fauna would be found in Europe. By the 

 commencement of the Tertiary epoch, most of this old fauna seems 

 to have disappeared; but in the Puerco beds of the United States, 



FIG. 30. UPPER MOLAR OF A SMALLER SPECIES OF Tritylodon. 

 Natural size and enlarged. 



and the equivalent deposits of Cernays, in the south of France, 

 which seem to form a transition between the Secondary and 

 Tertiary, the Multituberculata still persisted, and it is noteworthy 

 that one genus (Neoplagiaulax] at least was common to the 

 northern half of the eastern and western hemispheres. 



It thus appears, so far as the available evidence permits of our 

 forming a judgment, that during both the Jurassic and Cretaceous 



