636 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
KEY TO THE SPECIES OF CHROICOCEPHALUS. 
a. Tarsus much longer than middle toe with claw, the latter decidedly shorter than 
exposed culmen. _ 
b. Tail entirely white; back, scapulars, and wings uniform neutral gray, the longer 
primaries partly black; head dark quaker drab in summer. (Atlantic and 
Gulf coasts of United States and West Indies; coast of western Mexico in 
winter; casual in Mississippi Valley.).Chroicocephalus atricilla, adults (p. 636). 
bb. Tail gray and blackish; scapulars, interscapulars, and wing-coverts grayish 
brown broadly margined with whitish or pale buffy; chest and breast brownish 
gray or grayish brown, like head and neck. 
: Chroicocephalus atricilla, young (p. 637), 
aa. Tarsus not longer than middle toe with claw, the latter longer than exposed 
culmen. 
b. Bill much stouter, its depth at gonydeal angle equal to more than one-fourth the 
length of exposed culmen, reddish; three outer primaries without white, except 
at tips. 
c. Tail white, shaded with gray on middle rectrices; back, scapulars, and wings 
uniform neutral gray, the longer primaries partly black and white; head 
dusky purplish gray and bill deep red in summer. (Interior of North 
America, south in winter to Peru, Chile, etc.). 
: Chroicocephalus franklinii, adults (p. 641), 
cc. Tail pale gray or grayish white with a broad subterminal band of blackish; 
back and scapulars grayish brown, some of the latter margined terminally 
with pale grayish buffy; bill blackish, with reddish or pinkish tinge basally. 
Chroicocephalus franklinii, young (p. 642). 
_ bb. Bill much more slender, its depth at gonydeal angle equal to less than one- 
fourth the length of exposed culmen, black; three outer primaries extensively 
white. 
c. Tail entirely white; back, scapulars, and wing-coverts uniform pale neutral 
gray; head very dark purplish gray in summer. (Whole of North America, 
breeding northward; southward in winter to Yucatan, Jalisco, etc.) : 
Chroicocephalus philadelphia, adults (p. 645). 
cc. Tail with a broad subterminal band of black; scapulars and interscapulars. 
grayish brown, tipped with pale buff; central area of lesser wing-covert tract 
CUBE Vi we ecerstercortmaaaraone ..Chroicocephalus philadelphia, young (p. 645). 
CHROICOCEPHALUS ATRICILLA (Linnzus). 
LAUGHING GULL. $ 
Adults in swmmer (sexes alike)—Head and upper half of neck 
(extending farther downward in front than bebind) plain dark sooty 
gray or dark quaker drab), darkest on upper neck; a small elongated 
spot of white on each eyelid; lower neck (all round), upper tail- 
coverts, tail, and under parts immaculate white, the under parts 
sometimes (in newly killed specimens) tinged with delicate pink; 
back, scapulars, wings, and rump uniform neutral gray, the tertials, 
secondaries and proximal primaries broadly tipped with white; five 
outer primaries black, with or without a small apical spot of white, the 
third, fourth, and fifth (from outside) with basal portion gray for a 
greater or less distance, this sometimes abruptly defined against the 
black of distal portion, sometimes shading gradually into it; remain- 
