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W. H. BURT 



appear to have a larger fauna, 229 to 160, but if we consider genera, 

 it would have the smaller fauna, 68 to 93. South America, with 

 114 generic names, tops them all. But this is not as bad as it might 

 seem at first glance. Obviously, if we are comparing faunas which 

 are relatively close geographically, and there are no great barriers, 

 most of the genera will be common, so we should use a smaller 



Fig. 1. Chart showing relationships of non-flying land mammals on 

 three continents. Number of genera is approximate. Shaded areas repre- 

 sent parts of total faunas. Formulas at bottom are for taxonomic 

 resemblance. 



category such as the species. If we are comparing remote faunas 

 where few, if any, of the species are common, we must use a higher 

 category, the genus or family. 



These are some of the items that one must consider when com- 

 paring faunas for resemblance. Now let us look at Fig. 1 and the 

 measures we get by using different formulas. Numbers of genera 

 listed in the literature are given in the left column and are plotted 

 to scale in the others. My intuition tells me that South America 

 has too many genera in the indigenous block, relative to North 



