CHAP. XIII. ] THE AUSTRALIAN REGION. 399 
know they have in the north. Perhaps a more important con- 
sideration is, that Didelphys is a family type unknown in Aus- 
tralia; and this implies that the point of common origin is very 
remote in geological time. But the most conclusive fact is that 
in the Eocene and Miocene periods this very family, Didel- 
phyide, existed in Europe, while it only appeared in America 
in the Post-pliocene or perhaps the Pliocene period; so that it 
is really an Old-World group, which, though long since extinct 
in its birthplace, has survived in America, to which country it 
is a comparatively recent emigrant. Primeval forms of marsu- 
pials we know abounded in Europe during much of the Secondary 
epoch, and no doubt supplied Australia with the ancestors of 
the present fauna. It is clear, therefore, that in this case there 
is not a particle of evidence for any former union between 
Australia and South America; while it is almost demonstrated 
that both derived their marsupials from a common source in the 
northern hemisphere. 
Birds offer us more numerous but less clearly defined cases of 
this kind. Among Passeres, the wonderful lyre bird (Menura) 
is believed by some ornithologists to be decidedly allied to the 
South American Pteroptochide, while others maintain that 
it is altogether peculiar, and has no such affinity. The Aus- 
tralian Pachycephalide have also been supposed to find their 
nearest allies in the American Vireonide, but this is, perhaps, 
equally problematical. That the mound-makers (Megapodiide) 
of the Australian region are more nearly allied to the South 
American curassows (Cracidz) than to any other family, is per- 
haps better established ; but if proved, it is probably due, as in 
the case of the marsupials, to the survival of an ancient and 
once wide-spread type, and thus lends no support to the theory 
of a land connection between the two regions. A recent author, 
Professor Garrod, classes Phaps and other Australian genera of 
pigeons along with Zenaida and allied South American forms ; 
but here again the affinity, if it exists, is so remote that the ex- 
planation already given will suffice to account for it. There 
remain only the penguins of the genus Hudyptes; and these 
have almost certainly passed from one region to the other, but 
