334: GEOGRAPHICAL AND GEOLOGICAL DISTKIBUTION. 



three or four more or less clearly defined species (E. hystrix or 

 aculeata, E. cetosa, E. acanthion*) inhabiting Australia and Tas- 

 mania, and a single one (E. Lawesii) New Guinea ; and Acantho- 

 glossus, represented by A. Bruijnii, from Northern New Guinea. 

 Fossil remains of this family are not numerous, and belong exclu- 

 sively to tlie Post-Pliocene deposits of the Australian continent. 

 Echidna Owcni is founded upon a portion of a humerus from Darling 

 Downs, and indicates an animal considerably larger than the com- 

 mon recent species. E. Ramsayi, from a breccia cave in Wellington 

 Valley, is likewise founded upon a humerus. 



Marsupialia. — All the existing members of this order, if we 

 except the single family of American opossums (Didelphidse), are 

 restricted to the Old World, and are in the main confined to the 

 Australian continent and New Guinea, a limited number of fprms 

 finding a habitat in the debatable tract between the Australian and 

 Oriental realms. The general features of their distribution are 

 discussed in the chapter treating of the Australian realm. The 

 order is not represented in either of the continents of Eurasia or 

 Africa. 



The opossums comprise a considerable number of species, the 

 majority of which are confined to South and Central America; 

 two species, Didelphys Virginiana and D. Californica, are found in 

 the United States, the former, the common American species, rang- 

 ing from the Gulf border to the State of New York. An aberrant 

 web-footed form, the yapock (Chironectes), inhabits South and 

 Central America. 



Marsupial remains in deposits older than the Tertiary are not 

 abundant, and are in the main comprised in a number of genera 

 whose exact relationships have not as yet been absolutely deter- 

 mined. Indeed, it is not a little doubtful whether the earliest 

 forms usually refeiTcd to this order — those from the Trias — actually 

 belong here, or represent an even more primitive type of mammal. 

 To this category of uncertain forms may be referred the Microlestes 

 antiquus, from the Keuper of Germany, M. Moorei and Hypsiprym- 



* Described by Collett from North Queensland (" Forli. Selsk. Christiania," 

 1884). Liltken indicates the possible existence of a fourtli Australian species 

 ("Proc. Zool. Soc," London, 1884, p. 150), while Dubois defines a supposed 

 new species, named Froechidna vlUosissima, from New Guinea ("Bull. MuB. 

 Belg.," iii., p. 109). 



