THYLACOLEO 397 



nearly double the size of that in the lion. The upper tuber- 

 cular tooth (m, i) resembles in its smallness and position that 

 in the placental Felines. But in the lower jaw the carnassial 

 (jy) is succeeded by two very small tubercular teeth (m, i and 2), 

 as in Plagiaulax (fig. 93, p. 320) ; and there is a socket close 

 to the symphysis of the lower jaw of Thylacoleo which indicates 

 that the canine may have terminated the dental series there, 

 and have afforded an additional feature of resemblance to the 

 Plagiaulax. 



The foregoing are some of the more interesting illustrations 

 of the law, that " with extinct as with existing Mammalia, par- 

 ticular forms were assigned to particular provinces, and that 

 the same forms were restricted to the same provinces at a 

 former geological period as they are at the present day."* 

 That period, however, was the more recent tertiary one. 



In carrying back the retrospective comparison of existing 

 and extinct Mammals with those of the eocene and oolitic 

 strata, in relation to their local distribution, we obtain indica- 

 tions of extensive changes in the relative position of sea and 

 land during these epochs, in the degree of incongruity between 

 the generic forms of the Mammalia which then existed in 

 Europe and any that actually exist on the great natural conti- 

 nent of which Europe now forms part. It would seem, indeed, 

 that the further we penetrate into time for the recovery of 

 extinct Mammalia, the further we must go into space to find 

 their existing analogues. To match the eocene Palseotheres 

 and Lophiodons, we must bring Tapirs from Sumatra or South 

 America, and we have to travel to the antipodes for Myrmeco- 

 bians, the nearest living analogues to the Amphitheres of our 

 oolitic strata. 



On the problem of the extinction of species, little, demon- 

 stratively, can be said; and on the more mysterious subject 



* Report on the Extinct Mammals of Australia, 1844. 



