FAUNA OF PARA 73 



the dissimilarity of the animal and vegetable productions 

 to those of other parts of Brazil. In fact, the Fauna of 

 Para, and the lower part of the Amazons, has no close 

 relationship with that of Brazil proper ; but it has a 

 very great affinity with that of the coast region of Guiana, 

 from Cayenne to Demerara. If we may judge from the 

 results afforded by the study of certain families of insects, 

 no peculiar Brazilian forms are found in the Para dis- 

 trict ; whilst more than one-half the total number are 

 essentially Guiana species, being found nowhere else but 

 in Guiana and Amazonia. Many of them, however, are 

 modified from the Guiana type, and about one-seventh 

 seem to be restricted to Para. These endemic species 

 are not highly peculiar, and they may be yet found over 

 a great part of Northern Brazil when the country is better 

 explored. They do not warrant us in concluding that 

 the district forms an independent province, although 

 they show that its Fauna is not wholly derivative, and 

 that the land is probably not entirely a new formation. 

 From all these facts, I think we must conclude that the 

 Para district belongs to the Guiana province, and that, 

 if it is newer land than Guiana, it must have re- 

 ceived the great bulk of its animal population from that 

 region. I am informed by Dr. Sclater that similar re- 

 sults are derivable from the comparison of the birds of 

 these countries. 



The interesting problem, how has the Amazons Delta 

 been formed ? receives light through this comparison of 

 Faunas. Although the portion of Guiana in question is 

 considerably nearer Para than are the middle and southern 

 parts of Brazil, yet it is separated from it by two wide 

 expanses of water, which must serve as a barrier to 

 migration in many cases. On the contrary, the land of 

 Brazil proper is quite continuous from Rio Janeiro and 

 Bahia up to Para ; and there are no signs of a barrier 

 ever having existed between these places within recent 

 geological epochs. Some of the species common to Para 

 and Guiana are not found higher up the river where it 

 is narrower, so they could not have passed round in that 

 direction. The question here arises, has the mouth of the 

 Amazons always existed as a barrier to migration since 

 the present species of the contiguous regions came into 

 existence ? It is difficult to decide the question ; but 

 the existing evidence goes far to show that it has not. 



