MARSUPIALS. 287 



aberrant genera are known, each having a single species, the one Hyracodon, from Ecuador, and 

 the other a web-footed aquatic animal about the size of a large brown rat, Chironectes (the Yapok) 

 from Guiana, which, strange to say, is said to be possessed of large cheek-pouches ; at least is so 

 described by Mr. Ogilby, although Wagner, probably with justice, questions the accuracy of his 

 observation. 



Thai the origin of the Opossuni belongs to the same period as that of the other Marsupials, 

 appears a reasonable assumption ; and its geographical position in a country nearest to the abode 

 of the other Marsupials, suggests a derivation of the one from the other by a connection between 

 these lands. At the same time, we are by no means shut up to this as the sole hypothesis which will 

 meet the facts. As at the eocene epoch Marsupial, if not the only, seems at least to have been 

 the principal form of Mammalian life over the whole globe, South America may have received and 

 retained her Opossums from the general stock from the northern hemisphere, or some other quarter, 

 without having had any communication with Australia. 



The fossil remains do not oppose such an hypothesis. Nmncrous remains of species have been 

 found in the bone-caves of Brazil, and are preserved in the British Museum. But Mr. Waterhouse 

 remarks that he has not found any, the size and proportions of which would lead him to suspect that 

 they belonged to species which are not known to exist at the jjresent day in Brazil.* No trace 

 of any species has been met with indicating anything closer or other than a general Marsupial 

 affinity with Australian species. 



The fossil remains which come nearest to the osteology of the Opossums is the well-known 

 specimen discovered by Cuvier in the eocene beds of the Paris basin, and named Didelphys Cuvieki 

 by Fischer. Biit although it is clearly marsupial and insectivorous, apparently identical with the 

 Opossums, it cannot be said to have been one beyond all doubt. Had it been found in a eountrj- of 

 Opossums (the Brazilian caves for example), we should have accepted it as such without hesitation ; 

 but the absence or imperfect condition of the incisors and premolars leaves it an open question. 

 Other remains of marsupial insectivora which constitute the genus Thylacotherium (Spalaco- 

 THERiUM of Owen) have been found in Em-ope, and some of them in much older formations (the 

 Stonesfield slate). 



Phalangers. — PiiALANGisTA. In the Placental species, a passage between the Mice and the 

 Squirrels can be made through the Dormice. A similar passage occurs in the Marsupials, from the 

 Phascogales on the one hand, to the Petauri and the Phalangers on the other, through a Dormouse- 

 like group named Dromicia. There are three species of them found in the east and south-west 

 divisions of the continent : their habitats being, respectively. New South Wales, Van Dieman's Land, 

 and West Australia. The Phalangers proper, which are regarded by Waterhouse and Owen as 

 the equivalents of the small Quadrumana, are all to be met with in the eastern region. Two of 

 them, indeed, have not been observed as occurring in New South Wales, but these are met with in 

 Van Dieman's Land or Victoria, which are both, geologically, parts of the eastern region of Australia. 

 Two of them are also foxmd in Western or rather South-western Australia, and one, Phalangista 

 VULPINA, occurs everywhere throughout the continent, and of course also in Northern Australia, 

 although, indeed, the identity of the specimens found in the northern region (Port Essington) 

 with the Ph. vulpina of the rest of the continent is not absolutely certain. Waterhouse says he 



* "Waterhouse's " Nat. Hist, of Mammals," vol. i. p. 529, 1846. 



