28 
Psyche 
March 
ditions. At the Busu River and in other lowland rain forest 
sites investigated, ant species tended to be segregated into 
local areas, sometimes a hectare in extent or less, which 
could be distinguished from adjacent areas by their specific 
canopy densities. When the total range of possible canopy 
densities at the Busu River, from the open aspect that 
fringes savanna areas, to the most closed aspect, ordinarily 
found covering sloughs, was arbitrarily divided into three 
divisions (open, medium, dense) and their faunas studied, 
the fohowing microgeographic segregation of ant species 
was noted. 
“Open rain forest”. (Plate 5) Broken canopy; consider- 
able ground insolation; leaf litter 2 to 15 cm. thick; leaf 
mold present but thin and relatively dry; soil loose, well 
aerated, and relatively dry; moss scarce on both ground 
and tree trunks ; A-stratum trees generally less than thirty 
meters high ; lianes and plank buttresses much less common 
than in other two divisions; recumbent vines common on 
ground; soil and rotting logs generally thoroughly pene- 
trated with dense root and rhizome growth; undergrowth 
relatively dense; sufficient to make human progress across 
the forest floor difficult. This is the aspect of old second- 
growth forest and may be created naturally by the fall of 
large forest trees or, in mountainous areas, by rockslides. 
It is also a more or less permanent feature of the fringe of 
forest, generally one to two hundred meters wide, that bor- 
ders savanna areas. Occasional spots deep within rain forest 
approach the open aspect even though an immediate cause, 
such as a large fallen tree, is not in evidence. Ant species 
that appear to reach their maximum density in open rain 
forest at the Busu River included Platythyrea parallela (Fr. 
Smith), Diacamma rugosum (Le Guillou), Odontomachus 
simillimus (Fr. Smith), and Cardiocondyla paradoxa 
(Emery). In the canopy of the open forest, species of 
Crematogaster, especially subgenus Xiphocrema, and of 
Technomyrmex increased generally, while those of Irido- 
myrmex decreased. 
“Medium rain forest”. (Plates 3, 4). By far the largest 
lowland area in the Lae area is covered by forest of the 
following aspect: closed canopy; ground insolation slight; 
