V fso^"l Allen, Origin and Distribution of N. A. Birds IAQ 



Zone,' interposed between and separating the Cold Temperate, 

 or 'Boreal,' from the Warm Temperate, or 'Sonoran' (1. c. pp. 

 30-33). This is equivalent to what is termed in this paper the 

 Alleghanian Zone, and forms the northern transcontinental belt 

 of the Warm Temperate. This zone was first recognized by 

 Dr. Merriam in the West as the ' Neutral or Pine Zone,' 1 and 

 correlated later with the Alleghanian Fauna of the East, as the 

 'Neutral or Transition Zone.' 



The Alleghanian Zone is beyond question a transition belt, 

 being necessarily so from its geographical position ; its affinities, 

 however, are decidedly with the Warm Temperate division of 

 the continent rather than with the Cold Temperate, as the case 

 was first interpreted by Dr. Merriam, 2 since its northern boun- 

 dary coincides closely with the northern limit of distribution of a 

 large number of southern genera of both plants and animals, 

 including most of the staple grains and fruits of the Warm Tem- 

 perate Zone. 



As is well known, there is always a belt of neutral territory 

 along the common boundary line of two adjoining areas, varying 

 in breadth with the rank of the two areas ; and the present case 

 of the Alleghanian Zone is thus not exceptional. All things con- 

 sidered it therefore seems best to regard it as the northern trans- 

 continental belt of the Warm Temperate, rather than to give it 

 the anomalous position of a minor faunal area interposed between 

 and completely separating two areas of a higher grade. 3 Besides, 

 the term 'transition,' for reasons already given, is not a distinc- 

 tive designation for a faunal area of any grade, although it has 

 been repeatedly used in this way by different writers ; its proper 

 function is that of a descriptive term — not a designation to be 

 used in a taxonomic sense. 



The various faunal areas recognized in the present paper 

 may be tabulated as follows : — 



1 N. Am. Fauna, No. 3, 1890, p. 11, map 5. 



2 N. Am. Fauna, No. 3, p. 20, and ibid., No. 5, p. 21. 



3 In biology 'aberrant,' 'transition' or intermediate genera are frequently met 

 with, and in some cases it is difficult to refer them to one of the two subfamilies to 

 which they are allied rather than to the other. Yet we feel compelled to refer them to 

 one or the other, or else to make a new subfamily for the aberrant genus, in case it 

 shows sufficient differentiation, rather than to leave it as an isolated genus, with the 

 rank of a genus, to be interposed between two subfamilies, or families, as the case 

 may be. 



