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CHAP, XVIl.l MAMMALIA, 253
The Wombats are tail-less, terrestrial, burrowing animals, about
the size of a badger, but feeding on roots and grass. They
inhabit South Australia and Tasmania (Plate XI. vol. i. p. 439).
An extinct wombat, as large as a tapir, has been found in the
Australian Pliocene deposits.
General Bemarks on the Distribution of Marsupialia.
We have here the most remarkable case, of an extensive and
highly varied order being confined to one very limited area on
the earth's surface, the only exception being the opossums in
America. It has been already shown that these are compara-
tively recent immigrants, which have survived in that country
long after they disappeared in Europe. As, however, no other
form but that of the Didelphyidse occurs there during the
Tertiary period, we must suppose that it was at a far more
remote epoch that the ancestral forms of aU the other Marsupials
entered Australia ;
and the curious little mammals of the Oolite
and Trias, offer valuable indications as to the time when this
really took place.
A notice of these extinct marsupials of the secondary period
will be found at vol. i. p. 159.
Order XIII.—MONOTEEMATA.
Family 83.—ORNITHORHYNCHID^. (1 Genus, 1 Species.)
General Distribution.