226 Mr. H. W. Bates's Contributions 



America, increase as we approach the eastern slopes of the Andes 

 and culminate in the neighbourhood of Bogota. There is a 

 feature in the atmospheric conditions of this region which ought 

 to be noticed in connection with this subject. Lieutenant Herndon 

 (the American traveller) and M. de Castelnau found on the eastern 

 side of the Peruvian Andes that the barometer and point of boil- 

 ing water became uncertain guides in the measurement of alti- 

 tudes. Lieutenant Herndon found that the boiling point at Nauta 

 in Peru gave only 434 feet of elevation above the sea level, and 

 that in descending the Amazons it increased, until, at Ega, the 

 result was 2,052 feet, decreasing thence gradually to the Atlantic. 

 As this result is evidently erroneous, he concludes that there is a 

 great increase of atmospheric pressure towards the foot of the 

 Andes. This phenomenon must have its weight in considering the 

 local conditions as affecting the features of the fauna of the district. 



With regard to the relations of the Amazonian fauna to that of 

 other regions of tropical America, I can say very little at present. 

 It has been classed,* together with Columbia, as one province. 

 It has most affinity with tliat of Guiana and less with that of South 

 Brazil, Recurring again for illustration to the genus Papllio, after 

 deducting nine widely distributed Neo-tropical species, eleven of 

 the remaining thirty-two are identical with Guiana species, and 

 five others may be considered as local sub-species of Guiana forms. 

 Three only of the thirty-two are found in Brazil, from Pernam- 

 buco southwards, and four in Venezuela. The proportion of these 

 thirty-two local species found in New Granada I cannot at present 

 ascertain. 



In compiling the catalogue of species, I shall make as few 

 alterations as possible in the nomenclature of previous authors ; 

 the chief innovations will be in the determination of the sexes. 

 I have been constrained to adopt the principle of treating every 

 distinct and constant local variety as a separate form ; giving 

 it a separate name, but pointing out always what I have thought 

 to be its true relation to the allied species. I have found it 

 quite impossible to enter into considerations on the geographical 

 distribution of the species without adopting this principle; for 

 when all local varieties (sometimes incorrectly considered so) are 

 forced together under one name and one definition, I think we 

 cannot come to any just conclusions regarding the true relations of 

 species, or make comparisons between different faunas. In fol- 

 lowing out this system many curious and interesting facts in geo- 

 graphical distribution come out in greater prominence. One is 

 the very different degree of variability of different species, in the 

 • Woodward's Recent and Ancient Fossil Shells, map and p. 402. 



