GENERAL AND INTRODUCTORY. 



world ; the insectivorous and carnivorous American opossums, Didelphyidce, 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 Didelphyidce 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 Ccenolestes 

 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 

 Epanorthidfle, 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 Ccenolestes 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. 



