GENERAL AND INTRODUCTORY. 3 
world; the insectivorous and carnivorous American opossums, Didelphyide, possessing 
no Australian representatives, but having apparently been independently derived from 
an earlier extensive race of the same order that formerly inhabited both Europe and 
North America, and that occurs in the fossil state in the Upper Eocene, Lower Miocene 
and other tertiary deposits of these two continents. It is, at the same time, through 
these extinct representatives of the Didelphyidw that it has been suggested * that 
the present marsupial fauna of Australia was originally connected with that of 
America, though in times probably anterior to that of the division of the earth’s surface 
into the two continents previously referred to. 
The discovery of a very interesting marsupial type that opens out a further | 
field for speculation in this direction has been quite recently recorded by Mr. Oldfield 
Thomas, the mammalian specialist at the British, Natural History, Museum: The 
species, which has been described by Mr. Thomas under the title of Conolestes 
obscurus in the Annals and Magazine of Natural History for November, 1895, and 
the ‘“ Proceedings of the Zoological Society” for the past year (1896), has been 
obtained from the neighbourhood of Bogota, in South America. Although its dimen- 
sions do not exceed those of an ordinary rat, it is of peculiar interest with 
reference to the fact that, while representing an entirely new family among the 
living marsupials, it may be most naturally assigned to the extinct group of the 
Epanorthide, which has hitherto been known only by fossil remains obtained from 
the early Miocene, or, according to some authorities, Eocene, deposits of Patagonia: 
Following up the clue indicated by Conolestes obscurus, it has been found that the 
form obtained from the neighbouring province of Ecuador, and originally described 
by Tomes under the title of Hyracodon fuliginosus, is a second species of this 
interesting genus. The derivation of these two types from an originally extreme 
southern, or notogeal, centre of distribution is thus obviously indicated. 
Among the other animal groups that contribute their quota towards demon- 
strating their apparent common derivation from an original continental centre of 
development, of which Australia formed a material constituent, that of the fresh- 
water fishes is, perhaps, the most interesting. One remarkable fish, Ceratodus Forsteri, 
now indigenous to but two rivers of Queensland, and known locally as the Mary or 
Burnett River Salmon, and also as one of several species of so-called Barramundis, 
is the most familiar with reference to its belonging to an order, the Dipnoi, of which 
*« Mammals, Living and Extinct,” by Sir William Flower and Richard Lydekker, p. 135, 1891. 
