ACROSS UNKNOWN SOUTH AMERICA 
the river. Numberless rubber trees were to be seen at 
that spot on the banks of the Arinos, and also on those of 
this new important tributary. 
Two kilometres farther, where the Arinos was 280 
metres wide, it looked just like a big lake of stagnant 
water. The country was quite open on the left side, first 
chapada then campos. 
By 9.30 a.m. we had a most wonderful display of 
clouds and radiations of what looked like so many mares’ 
tails from the west-southwest. The river at that point 
flowed for one kilometre in a direction due south. We 
came to a basin 300 metres across with a spit of white 
sand on the northwest side. In this basin was an island, 
Nattali Island, 200 metres long, 20 metres wide, 10 feet 
above water, with a fine beach of sand and gravel on the 
south side. Gravel mounds were innumerable in the 
centre of this stream. 
After we had gone some eight kilometres farther down 
my men shot an ariranha. They had a belief that these 
ariranhas would easily kill a man in the water. As we 
have already seen, they certainly had a great craving for 
blood and were always brave in attacking. My men called 
them “water leopards.” In fact, the head of the ariranha 
was not unlike the head of a cat or a leopard. Although 
shot through the body two or three times, the ariranha 
actually came thrice to the attack of the canoe — so that 
my men were able to seize it by the tail and pull it inside 
the canoe while it was in a dying condition. 
Sixteen kilometres farther down we came to another 
beautiful tributary with delightfully clear water, six 
metres wide where it met the Arinos. One hundred 
metres lower down another little tributary, only four 
metres wide, also on the right bank, joined our stream. 
The first tributary seemed to come from the northeast. 
At the mouth of this tributary was a spot which would 
have made an ideal halting-place, but as it was too early 
68 
