66 ft. W. SHÜFELDT. 



True relationships, in fhe case of any group or groups, can 

 only be discovered through the application of the sum of our 

 knowledge of the forms to be classified to the solution of the 

 problem. 



Our knowledge of the kind referred to, falls into several 

 distinct departments, as for example, palaeontology, geographical 

 distribution, morphology, physiology, habits, and other conside- 

 rations. As to the pictorial and printed methods of exhibiting 

 and expressing our views upon the classification of the Mam- 

 malia, what I have said in the case of Birds in the above 

 cited paper is equally applicable to the Class here to be con- 

 sidered, and upon that account renders repetition in this place 

 unnecessary. 



As will be seen beyond, the lineal scheme has been 

 adopted, as in the case of Aves, though with the view of making 

 the classification clearer and more useful generally, I have given 

 the vernacular name of a typical example of each family in 

 parentheses, immediately following its scientific name in the 

 scheme. 



As but comparatively few fossil birds have been discovered 

 and described, and the relationships of these to existing forms 

 being more or less evident, or often shedding light upon the 

 subject, — these extinct avian species were incorporated into the 

 classification I made of the existing families and higher groups 

 of the Class. Now in the scheme of classification here presented 

 of the Mammalia, this feature has been omitted, owing to the 

 several facts that a very much larger number of fossil mammals 

 have been described than birds; they elucidate more the origin 

 and lines of descent of certain existing mammalian families 

 rather than they do the relationships of the latter; finally, in 

 not a few instances their relations to existing mammals is not 

 entirely clear, and where it is, the fossil forms would merely 

 tend to swell the list of the existing ones, without adding any- 

 thing to the value or completeness of the taxonomy proposed. 



