THE AMERICAN FAUNA AND ITS ORIGIN. 
199 
While both crocodiles and alligators are in America, the 
genus Alligator is restricted to that continent ranging south- 
wards from the Lower Mississippi, but it is not in the West 
Indian islands. The third family of the order Crocodilia, 
Gavialidse, is entirely absent from the western continent. 
The order Chelonia has all its families represented. Tortoises 
are abundant in both North and South America, and the marine 
turtles are in the warm seas on the coasts of the tropical 
regions. 
Of the Amphibia, six out of twenty-two families are peculiar 
to America, and all the others except two are to be found in 
one or other parts of the continent, so that there are twenty 
out of twenty-two families represented in the New World. Of 
the salamanders there are several genera, of the toads six 
genera, and of the frogs eight genera. Rana, the typical genus 
of frogs, is not in South America, but abundant in Central and 
North America. The well known frog of this country, Rana 
temeraria, and the edible frog of France, R. esculenta , are, however, 
not known in America. The remarkable animals called tree 
frogs have many species in America, three families of these 
amphibians being represented, two in the Nearctic and all three 
in the Neotropical region. 
The American Fauna compared with that of the 
Old World. 
Such is the great difference between the vertebrate faunas of 
the northern and southern parts of America that it is necessary 
to consider each separately, and to compare the one with the 
fauna of the northern and the other with that of the southern 
part of the Old World. Thus the faunas of the Nearctic and 
Palsearctic regions may be conveniently and usefully compared, 
and the fauna of the Neotropical region with the animals of the 
southern lands of the Old World, comprising the Ethiopian, 
Oriental and Australian regions, which I will call by the 
comprehensive term, Pakeotropical. 
For brevity as well as clearness these comparisons are best 
stated by a tabular arrangement. In these, as given below, 
the first column contains the names of the families represented 
in the American region and not in the corresponding one of the 
Old World, in the second and middle column is stated the 
families common to both the New World and the Old World 
regions ; and in the third column are the names of the Old 
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