1920] Swarth: Revision of Avian Genus Passerella 97 



those forms of the Sehistacea group that most nearly approach the 

 Unalaschcensis group are distinctly browner of coloration than the 

 more southern subspecies. It seems probable that while the habitats 

 of these unlike forms approach one another somewhat closely at certain 

 extreme outposts, these several points are termini of lines whose begin- 

 nings lie far apart, lines which have approached this meeting ground 

 from different directions. On the whole it may be admitted that the 

 three groups within the species Passerella iliaca, the Iliaca, Unalasch- 

 censis and Sehistacea groups of subspecies, are quite sharply differ- 

 entiated. Within each group the several subspecies grade from one 

 to another by variation so continuous that it is frequently extremely 

 difficult to draw differentiating lines. As regards each aggregation, 

 between Iliaca and Unalaschcensis, Iliaca and Sehistacea, or Unalasch- 

 censis and Sehistacea, there are (except for one limited series [see 

 p. 123]) no breeding birds at hand demonstrating intergradation. 

 ■ There are, however, certain facts pointing definitely to the existence 

 of such intergradation, Altivagans is undoubtedly a step from iliaca 

 toward sehistacea, and it comes from just the region where such 

 variation should occur. There are winter birds at hand that are 

 unmistakably intermediate in appearance between the several groups. 

 Also, a most important consideration, the stretch of country between 

 the known boundaries of the subspecies of the Iliaca group, the 

 Unalaschcensis group, and the Sehistacea group, includes just the 

 region where no intensive bird collecting has been done, where we 

 have no knowledge whatever of the breeding fox sparrow population. 

 So altogether it seems safe to say that, admitting the much sharper 

 differentiation existing between the several groups, as compared with 

 the closer connection of the several subspecies of each aggregation, 

 all the races should still be regarded as variants of one species, and 

 not of three. 



In the Sehistacea group are found the "slate-colored" and 

 "thick-billed" sparrows, so called, the subspecies sehistacea, fulva, 

 megarhynchus, Irevicauda., canescens, monoensis, nvariposae, and 

 stephensi. This group is more widely different from the Iliaca and 

 Unalaschcensis groups than these are from one another, and there is 

 also greater divergence between subspecies within the group than 

 there is in either of the other aggregations. 



These birds are nof so plump and rounded in appearance as are 

 the northwest coast and eastern subspecies. Tail is longer than wing, 



