I20 THE AMERICAN NATURALIST. [VorL. XXXV. 
the only arboreal character presented, the other digits remain- 
ing normal. But in Micoureus and Philander there is, in addi- 
tion to the opposability of the hallux, an enlargement of the 
fourth digit. In the Phalangeridz (Fig. 1, 4) there is super- 
added to both of these a reduction and syndactylism of the 
second and third digits. 
One member of the Phalangeridz, Tarsipes (Fig. 1, c), which 
is unique in many other respects, is the only marsupial pre- 
senting the latest stage of arboreal modification.  Tarsipes 
shows, in addition to all of the arboreal characters of the 
typical phalangers, a recession of the claws of the fourth and 
fifth digits. : 
To the second series belong the remaining members of the 
Australian fauna, the dasyures and their relatives (Dasyuridz), 
the wombats (Phascolomyidz), the bandicoots (Peramelidz), 
and the kangaroos and wallabies (Macropodida). These ani- 
mals are mainly terrestrial, but they all show arboreal modifica- 
tions of the foot. 
The dasyures have a functionally tetradactyl foot, derived 
from a pentadactyl one by reduction of the hallux. Various 
stages of this reduction are illustrated in the family ; Smin- 
thopsis murina (Fig. 1, d), for example, shows a well-formed 
hallux, while Antechinomys laniger (Fig. 1, e) has none at all. 
Wherever the hallux is indicated, however, it is of the opposa- 
ble type. As in the Didelphyidz, this is the only arboreal 
character represented in the family. 
In the wombats (Fig. 1, f) arboreal characters are more 
numerous. The hallux is here reduced to a tubercle, but its 
transverse position proves it.to have been formerly opposable. 
In addition, there is a slight syndactylism and reduction of the | 
second and third digits. 
The bandicoots have a functionally monodactyl foot, derived 
from a pentadactyl one by an enlargement of the fourth digit 
and a corresponding reduction of the others, notably the first, 
second, and third. It shows all of the arboreal characters of 
that of the typical phalangers. The least departure from the 
phalangerine condition is seen in Perameles doreyana (Fig. 1, g) 
in which the only pronounced modification is a reduction of the 
