218 PALMER, The Maryland Yellow-throat. se 
8. Slight facial black, short { ra/phr, Northeastern Mexico. 
wings, long tail, pale col- | poliocephala, Mexico. 
oration, grayish dorsum @ { Aalpebralt's, Mexico. 
without black. Subgenus | cantnucha, Guatemala. 
Chamethlypis.. leatercuee Costa Rica. 
g- Short and broad facial black, f 
slight slaty crown band, J 
Tee formosa’, Southeastern U.S. 
sexes nearly similar. { 
In groups 4, 5,6 and 7 there isa sequence of structure and 
color values, largely geographical and not present in the other 
groups. Seemingly, group 8 continues the sequence from group 
7. The intense, rich coloration of group 6 evidences the values of 
a moist tropical habitat. The short boreal summer residence of 
group 3 has hardly effected their color values. The habitats 
of all the groups except 8 and g do not overlap in summer, they 
rather meet and often intergrade. Theranges of 8 and g overlay 
the general habitats of some of the others, but the local environ- 
ments are quite different. The differences between the forms do 
not always indicate a variation from acontiguous form, but rather 
a specialization from an ancestral generalized type through envi- 
ronmental influences. 
In all the forms, except groups 3 and g, the wings are well 
rounded, the outer primaries being quite short, the third or fourth 
being the longest. This is a character common to all non- 
migrating and especially sedentary tropical species. In agzlis of 
group 3, the wing is long and pointed, the outer primary being 
as long as, or, in fully adult birds, slightly longer than the second. 
In folmiei and philadelphia an intermediate stage is evident, and 
these are birds of fairly high altitudes with a long migration. As 
we pass southward and toward sea level in the habitats of these 
birds, we find that the outer primary decreases in length, thus, 
brachidactyla has a longer and more pointed wing than any of 
group 4, because it migrates further, it goes further north and 
south. As the birds of group 3 and g and dbrachidactyla of group 
4, migrate more extensively than any others of the genus, it is 
evident that the long, pointed wing with a long outer primary, as 
compared with the short, well rounded wing and short outer pri- 
mary of their slightly migrating or sedentary relatives, is an index 
‘Subgenus Oforornis. 
