Vol. 35, pp. 181-218 October 17, 1922 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



f'r- 

 (.. 

 STUDIES IN THE TYRANNID^. ^^ 



III. The South American Forms of Myiarchus. ^ i>' .!^' 



BY W. E. CLYDE TODD. 



Myiarchus is one of those involved groups of closely related 

 forms which from the very beginning has been a source of 

 trouble to the systematic ornithologist. With the same pattern 

 of coloration running through the entire group, and such incon- 

 spicuous variations in form and proportion, it is little wonder 

 that authors have often failed to appreciate the value of the 

 characters of the specimens they handled, or to differentiate the 

 forms represented. The small amount and usually poor quality 

 of the available material have of course contributed largely 

 towards the confusion from which the present group, in common 

 with many others, has suffered. Mr. Ridgway, in the fourth 

 volume of his great work on "The Birds of North and Middle 

 America," having so satisfactorily elucidated the various forms 

 of Myiarchus found in that section, it remains to work out the 

 South American forms on the same Hues. The present paper 

 is offered as an attempt toward this end, and has been made 

 possible as a result of the activities of several institutions in 

 various parts of South America in recent years. No less than 

 nine hundred and sixty-three specimens, including considerable 

 typical and topotypical material, have been examined in the 

 course of the present investigation. Of these four hundred and 

 two are in the collection of the Carnegie Museum. The re- 

 mainder have been loaned by the various institutions specified 

 in Part I of the present series of papers, and our thanks are due 

 to these parties, and also to Dr. Wilfred H. Osgood of the Field 

 Museum of Natural History, Dr. E. W. Nelson of the Bureau of 

 Biological Survey, and to Mr. Thomas E. Penard of Arhngton, 



36— Proc. Biol. Soc. Wabh., Vol. 35, 1922. (181) 



