18 
ISLAND LIFE. 
[part I. 
while allied species come to the north bank, which in like 
manner forms their boundary. As examples we may mention 
that one of the Saki monkeys ( Pitkecia monachvs ? ) comes up 
to the south bank of the Upper Amazon, while immediately 
we cross over to the north bank we find another species 
(. Pithecia rufibarbata ? ). Among birds we have the green 
jacamar ( Galbula viridis), abundant on the north bank of the 
Lower Amazon, while on the south bank we have two allied 
species ( Galbula rufoviridis and G. cyaneicollis ) ; and among 
insects we have at Santarem, on the south bank of the Ama- 
zon, the beautiful blue butterfly, Callithea sapphira, while almost 
opposite to it, at Monte-alegre,an allied species, Callithea Leprieuri 
is alone found. Perhaps the most interesting and best known 
case of a series of allied species, whose ranges are separate but 
conterminous, is that of the beautiful South American wading 
birds, called trumpeters, and forming the genus Psophia. There 
are five species, all found in the Amazon valley, but each 
limited to a well-marked district bounded by great rivers. On 
the north bank of the Amazon there are two species, one in its 
lower valley extending up to the Rio Negro, and the other in 
the central part of the valley beyond that river j while to the 
south of the Amazon there are three, one above the Madeira, 
one below it, and a third near Para, probably separated from 
the last by the Tocantins river. 
Overlapping areas among the species of a genus is a more 
common phenomenon, and is almost universal where these 
species are numerous in the same continent. It is, however, 
exceedingly irregular, so that we often find one species extend- 
ing over a considerable portion of the area occupied by the 
genus and including the entire areas of some of the other 
species. So little has been done to work out accurately the 
limits of species that it is very difficult to give examples. One 
of the best is to be found in the genus Dendrceca, a group of 
American wood-warblers. These little birds all migrate in the 
winter into the tropical regions, but in the summer they come 
north, each having its particular range. Thus, D. dominica 
comes as far as South Carolina, D. coerulea to Virginia, I). dis- 
color to Southern Maine and Canada; four other species go 
