1916] Dice: Land Vertebrates of Southeastern Washington 299 



but in the present paper an association is not considered to extend be- 

 yond the limits of a single faunal area. 



The lines separating the different faunal areas are not sharp. Prob- 

 ably the best criterion for characterizing faunal areas is the dominance 

 of particular habitats. It is evident that in passing from one area to 

 another a situation will be met where the dominant habitat of one area 

 will equal in extent the dominant habitat of the other area. It is at 

 this point that the line separating the two must be drawn. -Each area 

 will usually show at its edges some development of the dominant 

 habitats of the adjacent areas. In many cases a dominant habitat 

 from one area may recur as a subdominant habitat throughout an 



Fig. B. Map of Walla Walla and Columbia counties, southeastern Wash- 

 ington, showing the extent of each of the three faunal areas, Columbia Basin 

 sagebrush area, Columbia Basin prairie area, and Blue Mountain area. 



adjacent area. However, it is best to consider each area in sections 

 where it is typically developed and not along its edges. 



Lists of the characteristic species of each of the faunas are given. 

 Each list includes those native breeding species which in southeastern 

 Washington are definitely known from only one faunal area. Lists 

 are also given of the species making up the different associations of 

 each fauna. As here given the lists record all the forms noted in each 

 of the corresponding habitats. Trapping records are included in some 

 instances to show the relative abundance of some of the smaller mam- 

 mals. Unless otherwise noted, only the results of the first night's 

 trapping on any trap line are included. Traps are usually set from 

 five to ten yards apart and in a continuous line. 



