472 
ZOOLOGY OF 
more satisfactory, because monkeys are animals so well 
known to the native hunters, they are so much sought 
after for food, and all their haunts are so thoroughly 
searched, and the localities for the separate kinds are so 
often the subject of communication from one hunter to 
another, that it is quite impossible that any well-known 
species can exist in a particular district, unknown to 
men whose lives are occupied in forming an acquaint- 
ance with the various tenants of the forests. 
On the south side of the Lower Amazon, in the 
neighbourhood of Para, are found two monkeys. My- 
cetes beelzebub and JaccJius tamarin, which do not pass 
the river to the north. I have never heard of monkeys 
swimming over any river, so that this kind of boundary 
might be expected to be more definite in their case than 
in that of other quadrupeds, most of which readily take 
to the water. 
Towards their sources, rivers do not form a boundary 
between distinct species ; but those found there, though 
ranging on both sides of the stream, do not often extend 
down to the mouth. 
Thus on the Upper Rio Negro and its branches, are 
found the Callitlirix torguatus, NyctipitJiecus triviryatus, 
and Jacchus (No. 21), none of which inhabit the Lower 
Rio Negro or Amazon; they are probably confined to 
the granitic districts which extend from Guiana across 
the sources of the Rio Negro towards the Andes. 
Among birds it cannot be expected that we should 
find many proofs of rivers limiting their range ; but there 
is one very remarkable instance of a genus, the three 
known species of which are separated by rivers, namely, 
