34 Merriam Geographic Distribution of Life. 



families to which they respectively belong. In explanation of 

 this extended range it is found that these genera inhabited North 

 America in pre-glacial times and as a consequence have become 

 acclimatized to a wider range of climatic conditions. The semi- 

 Tropical belt of Florida is not known to possess any tropical 

 mammals except bats and a large indigenous mouse (Sitomi/* 

 moeropifs)*, but it has not been explored by experienced mam- 

 mal collectors. Still, its recent origin and complete isolation 

 from other tropical areas would indicate the absence of ter- 

 restrial species derived from the south. At the same time it is 

 known to be rich in tropical plants, land shells, insects, and birds, 

 as is shown in another part of the present paper (see pp. 51-53). 

 It contains 9 genera of tropical birds, namely, Zenaida, Gentry yon, 

 Starncenas, Rostrhamus, Polyborus, Crotophaga, Euetheia, CaUicheli- 

 don, and Ccereba. 



The following 62 genera of mammals belong to the North 

 American Tropical Region. The nine preceded by the letter S 

 enter the southern United States, which they penetrate varying 

 distances. Nyctinomus and Otopterus inhabit the Lower Sonoran 

 Zone in common with the Tropical ; Didelphis pushes completely 

 through the humid division of the Sonoran Region ; and Felis 

 and Procyon enter the lower edge of the Boreal. 



NORTH AMERICAN TROPICAL GENERA. 



* Described by the writer as ///*/> 

 4, Oct., 1890, p. 5:}. 



