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THE AMERICAN NATURALIST [Vol. XLII 



eastern deciduous 'forest region, and still others char- 

 acteristic of the northeastern coniferous forest region, 

 etc. For these reasons it seems to me that careful faunal 

 studies must contribute very materially to our knowledge 

 of the affinities and relationships of forms. 



Among the biotic regions that have been recognized in 

 North America, the prairie region is one of the most 

 interesting. It consists in general of a narrow zone 

 separating the eastern forest from the semi-arid plains, 

 as shown on the accompanying map. In Iowa, Illinois, 

 northern Missouri, and southern Minnesota and Wiscon- 

 sin, it widens into a wedge that extends to the western 

 boundary of Indiana. Pound and Clements (1900), 

 Transeau (1905), Bray (1901) and Sargent (1884) have 

 shown that both the environmental conditions and the 

 flora of this region are characteristic, but so far as I know 

 the vertebrate life has never, as a whole, received exami- 

 nation. 



During the past summer, the writer conducted an ex- 

 pedition 1 for the University Museum, University of 

 Michigan, to northwestern Iowa, for the purpose of in- 

 vestigating the fauna of that region. The collections 

 obtained by this expedition furnished a very representa- 

 tive series of the vertebrates of the prairie region, and a 

 careful study of the data seems to lead to three funda- 

 mental conclusions. 



1. The peculiar environmental conditions of the prairie 

 region have an effect upon the vertebrate fauna. This 

 is shown by the fact that many groups become modified 

 as they enter this region from the adjoining ones. Note 

 the following examples: 



(a) I have elsewhere shown that as the snake 



cipal range is to the eastward • 

 the following instances : 



1 Detailo-I reports will upprar upon rl 



