1894- PAL^ ARCTIC AND NEARCTIC REGIONS. 437 



Looking through the preceding Hsts, we find a remarkable 

 divergence in the characteristic groups of the two regions. Out of 

 fifteen genera of Insectivora, only two are common to both regions ; 

 an amount of difference which, if it occurred among larger and 

 better known animals, would produce a striking effect of diversity. 

 In the Carnivora there is a much smaller proportion of peculiar 

 genera, but this is to some extent counterbalanced by each region 

 possessing two families absent from the other. Ungulata, again, show 

 considerable diversity, the Palaearctic Region possessing ten genera 

 and the Nearctic five which are not found in the other. Only five 

 genera are common to both, and of these five, two, Rangifer and 

 Alces, are arctic, while two others, Ovis and Bos, have one species 

 each in the Nearctic Region against about thirteen between them in 

 the Palaearctic. The Rodents, again, have only eleven genera 

 common to both regions, while the Palaearctic has sixteen and the 

 Nearctic seventeen which are not found in the other region. 



The following summary will enable us to see the total amount of 

 similarity and difference : — 



SUMMARY OF DISTRIBUTION. 



Orders. , —-Families. ^, Genera. , 



No. of Genera. Palcsarctic. Both. Nearctic. Palcearctic. Both. Nearctic. 



Cheiroptera ..ir i 2 i 3 4 4 



Insectivora . . 15 12 o 8 25 



Carnivora .... 22 2 6 2 6 9 7 



Ungulata .... 20 2 2 2 10 5 5 



Rodentia .... 44 2 7 2 16 11 17 



Marsupialia . . i 00 i o 01 



« 19 8 43 31 39 



Total Genera ..113 — — — 74 — -70 



Total Families . . 27 27 



Here we see that in both the regions the number of genera not 

 found in the other largely exceed those common to both, the pro- 

 portion of the total genera thus limited being 58 per cent, in the 

 Palaearctic, and 56 per cent, in the Nearctic Region ; while in each 

 case out of a total of 27 families no less than 8 are so limited. If we 

 compare this amount of diversity with that between the Ethiopian 

 and Oriental Regions, we shall find that, while as regards genera it is 

 somewhat less, as regards families it is considerably greater. In the 

 Oriental Region out of a total of about 72 families of mammals only 8 

 are not Ethiopian ; while in the Ethiopian region out of about 74 

 families only 10 are not Oriental. No doubt these two regions are 

 those which most resemble each other, and they have been united by 

 some naturalists, but they are now generally admitted to be sufficiently 

 distinct to be classed as separate regions. Great weight has, however, 

 always been given to the possession of peculiar families ; and for the 

 same reason the fact that nearly one-third of the families in the 



