18 ISLAND LIFE 



each other, each species occupying an area of its own 

 Avhich rarely coincides exactly with that of any other 

 species of the same genus. In some case.s, when a river, 

 a mountain-chain, or a change of conditions as from 

 pasture to desert or forest, determines the range of species, 

 the areas of two species of the same genus may just meet, 

 one beginning where the other ends ; but this is compara- 

 tively rare. It occurs, however, in the Amazon valley, 

 where several species of monkeys, birds, and insects come 

 up to the south bank of the river but do not pass it, 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 {Pithecia monachus ?) 

 comes up to the south bank of the Upper Amazon, while 

 immediately we cross over to the north bank Ave find 

 another species {Pithecia Qmjiba7'hata ?). Among birds we 

 have the green jacamar {Galhula viridis), abundant on the 

 north bank of the Lower Amazon, while on the south 

 bank we have two allied species (Galhula rufoviridis and 

 G. cyaneicollis) ; and among insects we have at Santarem 

 on the south bank of the Amazon, the beautiful blue 

 butterfly, Callithca sa^^plmxt, while almost opposite to it, at 

 Monte-alegre, an allied species, Callithca JjCiwicuri is alone 

 found. Perhaps the most interesting and best known 

 case of a series of allied species, Avhose ranges are separate 

 but conterminous, is that of the beautiful South* American 

 wading birds, called trumpeters, and forming the genus 

 Psophia. There are five sj^ecies, 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 jDart of the valley 

 beyond that river ; 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 



