126 Nelson Names of Certain North American Bird^ 



The birds of this genus in western Mexico ha-ve hitherto been 

 considered specifically distinct from those of eastern Mexico but 

 the series in the Biological Survey Collection show that about 

 the Isthmus of Tehuantepec and southward intergradation takes 

 place so that a rearrangement of the Mexican forms becomes 

 necessary. The South American species becomes Tangavius 

 armenti (Cabanis) and the Mexican species should stand as fol 

 lows : 



Tangavhts emeu* wiieus (Wagler) Western Mexico. 



u u assimilis (Nelson) Southwestern Mexico. 



(( a involucratuA (Lesson) Eastern Mexico. 



