1917.] 



Chapman, Distribution of Bird-life in Colortibia. 



119 



district of eastern Panama, but from the lower Atrato Valley westward it 

 merges so completely with the Colombian-Pacific Fauna that any attempt 

 to map their respective boundary lines in this region must be purely arbi- 

 trary. 



The Cauca-Magdalena Fauna possesses comparatively few species pecu- 

 har to itself, its life consisting chiefly of forms received from the Ama- 

 zonian region on the east and Colombian-Pacific Fauna on the west. The 



Fig. 10. Known range of Thamnophilus nigriceps Scl. A species of the huinid Colombian-Pacific 

 Fauna of the Tropical Zone. 



result is a composite group to which neither of the above names could 

 properly be appHed. The region, however, is more than a meeting ground 

 for species originating elsewhere. It contains a number of such strongly 

 marked indigenous forms as Capita hypoleucus, Xenerpestes minlosi, and 

 Gymnostinops guatamozinus, and for this reason, as well as for convenience 

 in descriptive zoogeography, it is deserving of faunal rank. 



