1202 REPORT OF NATIONAL MUSEUM, 1898. 



and Dipnoaii fisbes, Pleurodire tortoises, aud Ratite and Trogonoid 

 birds; aud differs from it in the absence of Arciferous Batracbia aud 

 Orotalid snakes, and presence of Dendraspid, Causid, Atractaspid, and 

 Viperid snakes. 



The Arctogcean Realm is characterized by the absence of types con- 

 spicuous elsewhere, and by the presence of a few peculiar forms. Among 

 fishes it lacks Dipnoi and Crossopterygia, Osteoglossidaj, Characinidic, 

 and Cichlidw. It lacks Pleurodire tortoises aud Katite birds. Gingly- 

 modous fishes aud Urodele Batracbia are nearly confined to it, merely 

 extending a little over the border of the Neotropical. Its Oryptodire 

 tortoises extend both into the Neotropical and Ethiopian. Anguid 

 lizards are confined to it. It shares most of its Mammalia with other 

 regions. The Insectivora it shares with the Ethiopian, aud its deer 

 aud camels with the Neotropical. The genus Ursus is very character- 

 istic, one aberrant species only extending into the Neotropical. 



From what has preceded it is seen that the primaiy differences 

 between the faunae of the realms are to be found to a large degree in 

 the lower Vertebrata, the fishes, Batracbia, and Keptilia. These forms 

 furnish stronger distinctions than the birds and mammals, owing to 

 their greater inability to traverse natural boundaries. Neglect of these 

 indications has led to much of the difference of opinion in the question 

 of geographical distribution, which has been founded principally on 

 the conditions presented by the birds and Mammalia. 



In this system fragments of existing or old continents, which have 

 been subjected to conditions unfavorable to particular forms of life 

 otherwise prevalent in them, are, as in the system of Sclater, disre- 

 garded. Thus, islauds generally are not regarded as presenting con- 

 ditions definitive of divisions of the first rank, as was done by Huxley 

 and Gill in the case of New Zealand, and Gill and Lydekker in the 

 Polynesian Islands. The temperate regions of Africa and South 

 America are certainly not separable from the tropical portions as 

 divisions of primary rank, as was done by Allen, who is followed as to 

 South America by Gill. With equal propriety western North America 

 might be separated from Mississippi and Atlantic North America, on 

 account of the great deficiency of its fish fauna. In estimating faunis- 

 tic affinities one has to give similarities over a given area more weight 

 than differences, where the differences are only due to absence of tyi)es. 



Finally, it must be remembered that there are geographic points of 

 transition between all the realms. 



THE ARCTOG/EAN REALM. 



This realm includes three regions, namely, tbe Fndian, the Holarctic, 

 and the Medicolumbian. I have already defined the first two in gen- 

 eral terms. The third is the Transitional of Heilprin, tlie Sonoran of 

 Merriam and Lydekker, and the Neotemperate of Town send. It 

 embraces what is left of the Nearctic of Sclater after the subtraction 



