account, we need not be surprised to find the Nearctic region somewhat less rich and varied in its forms of life than the Palæarctic or the Australian regions, with which alone it can fairly be compared. The wonder rather is that it should be so little inferior to them in this respect, and that it should possess such a variety of groups, and such a multitude of forms, in every class of animals. [Illustration: NEARCTIC REGION] {115}_Zoological characteristics of the Nearctic Region._--Temperate North America possesses representatives of 26 families of Mammalia, 48 of Birds, 18 of Reptiles, 11 of Amphibia, and 18 of Fresh-water Fish. The first three numbers are considerably less than the corresponding numbers for the Palæarctic region, while the last two are greater--in the case of fishes materially so, a circumstance readily explained by the wonderful group of fresh-water lakes and the noble southward-flowing river system of the Mississippi, to which the Palæarctic region has nothing comparable. But although somewhat deficient in the total number of its families, this region possesses its full proportion of peculiar and characteristic family and generic forms. No less than 13 families or sub-families of Vertebrata are confined to it, or just enter the adjacent Neotropical region. These are,--three of mammalia, Antilocaprinæ, Saccomyidæ and Haploodontidæ; one of birds, Chamæidæ; one of reptiles, Chirotidæ; two of amphibia, Sirenidæ and Amphiumidæ; and the remaining six of fresh-water fishes. The number of peculiar or characteristic genera is perhaps more important for our purpose; and these are very considerable, as the following enumeration will show.