102 Br. R. W. Shufeldt on tJie 



These investigations, as many are aware, have not been con- 

 fined entirely to recent avifaunse, but have also taken into 

 consideration fossil material, the remains of birds that existed 

 as far back as Tertiary time. 



So far as the United States ornis is concerned, every family, 

 or, indeed, nearly every genus of the recent age, has thus been 

 dealt with, and some of the MSS. presenting the details of 

 these researches have been published, while the far greater 

 proportion of them temporarily await a similar disposition. 

 It is in this manner that such groups as the Passeres, the 

 Swifts, the Humming-birds, the Goatsuckers, the Trogons, 

 the Kingfishers, and many others have been gone over and 

 issued in the form of memoirs in difierent publications, while 

 upon the other hand the osteology of entire groups has been 

 written out and illustrated, and will, when printed, fill in gaps 

 that formerly existed. Among these last, extensive work has 

 also been done with large and small groups of birds not 

 occurring in this country, as the Penguins, the Ostriches, and 

 others. These will not be taken especially into consideration 

 in the present connexion, for the reason that considerable 

 unanimity of opinion exists among naturalists with respect to 

 their taxonomy ; though probably the Penguins form an ex- 

 ception to this statement. Commencing in the United States 

 avifauna with the Pygopodes, however, and passing the 

 various groups in review, following their linear arrangement 

 in the order in which they are usually printed, we meet not only 

 with single species but with groups of species, as to the true 

 taxonomic position of which in the system ornithologists enter- 

 tain very diverse opinions. It is to these that it is my inten- 

 tion to refer in the present paper. They have all been closely 

 studied osteologically, and in the case of many of them their 

 general anatomy has been investigated and their biology as a 

 whole given weight. My views upon the classification and 

 systematic position of some of these families or species now in 

 my mind have been briefly abstracted and published either in 



* The Ibis ' of the British Ornithologists' Union or in the 



* Proceedings ' of the Zoological Society of London. Others 

 there are that have not been so noticed. 



Prior to passing to the aforesaid subject-matter in chief, 

 however, it may be as well first to pay some attention to the 

 morphological characters of birds, witli special reference to 

 their use in determining a scheme for the natural classification 

 of the class. By the natural classification of Aves is meant 

 an orderly arrangement of existing birds into major and minor 

 subdivisions according to their tiue nffinities as tliey actually 

 obtain in nature. That a real relationship exists among 



