396 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
half (sometimes two-thirds or more) of maxilla; loral and malar antize 
on same vertical line or the former slightly posterior to the latter, 
or (in P. tahittensis) the loral antia decidedly anterior to the malar 
antia; mental antia extending nearly if not quite to anterior end of 
nostrils; frontal antia forming a deeply concave line across base of 
culmen. Wing ample, pointed, the outermost primary longest and 
exceeding distal secondaries by decidedly more than half the length 
of wing; tertials elongated, but the longest falling short of tips of 
three longest primaries. Tail nearly two-fifths as long as wing (some- 
times longer, sometimes shorter, than exposed culmen), slightly 
rounded, sometimes with middle pair of rectrices slightly shorter 
than next pair; rectrices, 12. Tarsus decidedly less than twice as 
long as middle toe without claw, transversely scutellate anteriorly, 
covered with hexagonal scales posteriorly; bare portion of tibia 
shorter than middle toe without claw, covered all around with hex- 
agonal scales; lateral toes decidedly shorter than middle toe, equal, 
or the outer toe slightly longer than the inner; hallux well developed 
but slender, elevated, decidedly shorter than basal phalanx of middle 
toe; interdigital spaces webbed basally, the web between middle 
and outer toes extending for length of basal phalanx of the latter, 
that between middle and inner toes slightly smaller; all the anterior 
toes margined laterally by a distinct tumid membrane. 
Coloration.—Pileum deep grayish brown or sooty, divided longitudi- 
nally by a median line of pale buffy and bordered along each side by 
broad superciliary stripe of the same narrowly streaked with dusky; 
a grayish brown or dusky loral and postocular stripe; general color 
of upper parts grayish brown, more or less varied with paler edgings 
or spotting; sides of head and neck, foreneck, and chest pale brown- 
ish buffy, streaked with grayish brown or dusky, the chin, upper 
throat, abdomen, etc., immaculate buff or buffy, white; one species 
with rump white. 
Range.—Northern parts of northern hemisphere in summer, nearly 
cosmopolitan during migration. (Three species.) 
KEY TO THE SPECIES AND SUBSPECIES OF PHX OPUS. 
a. Feathers of thighs without bristle-like tips; tail grayish brown, narrowly and 
sometimes indistinctly barred with darker. 
b. Rump, axillars, and under wing-coverts white, or prevailingly white. 
(Phzeopus phxopus.) 
c. Rump immaculate white or with only a few (mostly concealed) darker mark- 
ings; axillars more narrowly and more sparsely barred; size averaging larger 
(wing averaging 237.7 in male, 240.5 in female; exposed culmen 81.2 in male, 
82.8 in female; tarsus 56.7 in male, 59.6 in female): (Northern Europein 
summer; south to Africa, India, etc., in winter; occasional in Greenland; 
accidental in Nova Scotia.).........- Phzopus pheopus pheopus (p. 397). 
cc. Rump always more or Jess (sometimes heavily) spotted; axillars more heavily 
and extensively barred; size averaging smaller (wing averaging 227 in male, 
