BIEDS OF NORTH AND MIDDLE AMERICA. 9 



(sometimes less than half as long), the rectrices (usually 12, but 

 sometimes only 10) usually rounded, never acuminate, terminally. 



The Formicariidas comprise one of the larger groups of birds 

 peculiar to the Neotropical region, but, like several others of the same 

 class, wholly absent from the Antillean Subregion. The group is 

 well represented in the whole of the extensive territory extending 

 from Costa Rica to southern Brazil, but reaches its greatest develop- 

 ment in number of species and genera in the great valley of the 

 Amazon and the Guianas. Dr. Sclater ^ recognizes 250 species 

 belonging to 33 genera — numbere considerably less than those that 

 are actually known at the present time.'' 



Among so great a number of species and genera there is, naturally, 

 great variation in size and form. Tlie smallest are no larger than a 

 Gnatcatcher {Polioptila), while the largest are fully equal to an 

 average-sized Jay; some resemble Shrikes, others Thrushes, Wrens, 

 Dippers, or other oscinine groups in their general appearance. They 

 are nearly all birds of plain plumage, none having any brilliant colors, 

 and most of the species are terrestrial, or nearly so, feeding, as their 

 name implies, largely upon ants, though perhaps less extensively so 

 than has been supposed; it having been stated by competent observers 

 that some species subsist more upon various forms of insect life which 

 the immense armies of ants, as they march across the forest floor, 

 startle from their hiding place among the dead leaves, etc., over 

 which they pass. 



Notwithstanding their mesomyodian larynx, many of the Formi- 

 cariidae are good songsters, some of them being conspicuous for their 

 vocal powers. 



The classification of this group is very difhcult, more so probably 

 than in the case of any other American family of birds. Indeed it 

 may be truly said that even the most recent attempts to present an 

 orderly and natural sequence of the genera are very far from satis- 

 factory. My effort to bring order out of chaos can be considered as 

 only partially successful, but it is hoped that some improvement at 

 least has been made in that direction. Undoubtedly better results 

 would have been reached had a better representation of the genera 

 and species been available; but unfortunately there are very many 

 species and several recognized genera which I have not been able to 

 examine in this connection. As in the case of many other groups, 

 the segregation of the species into genera has been based far too 

 much on general resemblance, and too little attention paid to struc- 

 tural characters. This may be said of nearly every group of birds; 

 but in the present instance it is difficult to understand how certain 

 associations could have been made. 



« Catalogue of the Birds in the British Museum, vol. xv, 1890, pp. 177-328. 

 & In hia Hand-List of the Genera and Species of Birds (vol. iii, 1901, pp. 9-45) 

 Dr. Sharpe enumerates 347 species and 38 genera. 



