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 course the chief interest of the genus, which may be "an unmodified survivor from Mesozoic times, and therefore from a time long before the Didelphyidae, Peramelidae, and Dasyuridae were differentiated one from the other." Another ancient feature (found in Jurassic mammals) is a mylo-hyoid groove upon the lower jaw, which, however, is not always present, and its existence has therefore been denied. The single species, M. fasciatus, is partly arboreal and partly terrestrial in habit, and feeds upon ants. It is a Western and Southern Australian form.



'''Fam. 2. Didelphyidae.'''—All the members of this family are pentadactylous. The teeth are fifty in number, arranged thus: I 5/4 C 1/1 Pm 3/3 M 4/4. The caecum is small; the pouch is generally absent; the tail generally long and prehensile.



The genus Didelphys contains most of the forms belonging to this family, including as it does some twenty-three species. The Opossums are mainly arboreal animals, insectivorous in their food; but the larger species eat reptiles, birds, and their eggs. Several of the small species carry their young, when able to leave the teats, on