486 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
one species (S. melanogastra) with under parts of body mostly black. 
Downy young buffy or brownish above, irregularly spotted or marbled 
with blackish; in one species (S. fuscata) streaked above with dusky 
and buffy grayish, in varying relative proportion.* 
Range.—Cosmopolitan. (Sixteen, or more, species.) 
KEY TO THE SPECIES OF STERNA. 
(Based on adults only.) 7 
a. Back, scapulars and wings clear gray, not darker (usually paler) than neutral gray, 
the tail white or mostly white; inner webs of primaries largely white. 
b. Pileum and nape immaculate white; under parts pale gray like upper parts; 
bill yellow with a subterminal band of black. (Coasts of southern South America, 
from Brazil to Chile; casual on Long Island and coast of New Jersey.) 
Sterna trudeaui (p. 488). 
bb. Pileum, at least partly, the nape wholly black; under parts white or if gray the 
color decidedly paler than that of upper parts; bill not yellow nor with a 
black subterminal band. 
c. Pileum entirely black in summer. 
d. Inner web of lateral rectrix gray or dusky terminally, the outer web entirely 
white; bill orange; tarsus 21.5-24.mm., middle toe 19.5-22.5 mm. (Temperate 
North America, in winter southward to Guatemala.)..Sterna forsteri (p. 490). 
dd. Inner web of lateral rectrix white throughout, the outer web gray or white; 
bill red or black; tarsus not more (usually much less) than 20 mm., middle 
toe not more (usually much less) than 19 mm. 
e. Outer web of outermost rectrix dark gray; under parts of body not pure 
white (more or less grayish); bill mostly red at all seasons; wing usually 
more than 235 mm. 
J. Tarsus, 17.5-20 mm., longer than middle toe without claw; tail forked 
for usually less than 102 mm.; under parts of body paler gray (pallid 
neutral gray to grayish white); bill and feet vermilion or orange-red 
(Northern Hemisphere; south in winter as far as southern Africa, 
India, and Brazil.) .....-.-..2...0....000- Sterna hirundo (p. 493). 
ff. Tarsus 13.5-17 mm., shorter than middle toe without claw; tail forked 
for usually more than 102 mm.; under parts of body deeper gray (pale 
neutral gray); bill and feet carmine red. (Northern portions of Northern 
Hemisphere in summer; said to winter in Antarctic Ocean.) 
Sterna paradiszea (p. 499). 
ee. Outer (as well as inner) web of outermost rectrix white; under parts of 
body pure white (often suffused with pink); bill mostly black in summer, 
red basally in winter; wing usually less than 235 mm. (Nearly cos- 
mopolitan in temperate and tropical regions, mostly along sea- 
CODBSIB. ) o-eie as ce scinenee cies wate ee ose S easerereie Sterna dougalli (p. 505). 
cc. Forehead and sides of crown white; a black stripe from bill to eye. (Coasts of 
Bering Sea and south ward to Kadiak Island and Japan.) 
Sterna aleutica (p. 510). 
aIt may be thatS. fuscata should be separated generically (as Onychoprion fuscata), 
on‘accountvof the conspicuously different young, both in down and in first plumage, 
and possibly some details of structure which, however, I have not been able to dis- 
cover. But in this case S. anxtheta and S. lunata, which have usually been asso- 
ciated ‘with S. fuscata must remain in Sterna, for they do not agree with S. fuscata in 
coloration‘of the young. 
