BIRDS OF NORTH AND MIDDLE AMERICA. 568 
ee. Depth of bill at gonydeal angle equal to or greater than distance from 
anterior end of nostril to tip of maxilla, and much greater than its depth 
at base; coloration of plumage with little if any white. 
Leucophzeus (extralimital).¢ 
dd. Hallux quite free from inner toe; tibia with lower third or more unfeathered. 
e. Bill very deep subterminally and compressed, its depth at the very 
prominent gonydeal angle greater than distance from anterior end of 
nostril to tip of maxilla and equal to about three times its transverse 
width or thickness at same point.............. Gabianus (extralimital).> 
ee. Biil not notably deep and compressed, its depth at gonydeal angle less 
than distance from anterior end of nostril to tip of maxilla, and much 
less than three times its transverse thickness at same point. 
/. Bill very long and slender, the exposed culmen longer than middle toe 
with claw, its length from rictus greater than length of tarsus, its 
greatest depth léss than half the distance from anterior end of nostril 
tostiprof mara s.oppsaroeseaasueee sae ines Gelastes (extralimital).¢ 
Jf. Bill shorter or stouter (or both), the exposed culmen shorter than 
middle toe with claw, its length from rictus shorter than tarsus, its 
greatest. depth more than half the distance from nostril to tip of 
maxilla. 
g. Adults with under parts wholly white, young with under parts white 
to medium grayish brown, but if the latter the color neither uni- 
form nor very dark (sooty). 
h. Summer adults with head and neck wholly white; young with 
rump and upper tail-coverts always spotted or barred with grayish 
or dusky, the back, scapulars, and wing-coverts streaked and 
mottled with grayish brown and whitish or buffy...Larus (p. 580). 
hh. Summer adults with head black, gray, or brown, forming a con- 
spicuous ‘‘hood” in contrast with white or pink of under parts; 
young with rump and upper tail-coverts immaculate white, the 
interscapulars, scapulars, and wing-coverts grayish brown mar- 
gined (but not streaked nor mottled) with whitish or buffy. 
i. Very large (wing more than 450 mm.); bill very large and deep, 
strongly decurved terminally, the gonydeal angle very promi- 
nent; downy young unspotted..... Ichthyaétus (extralimital).@ 
“4 Leucophaeus Bruch, Journ. fiir Orn., 1853, 103 (type, by original designation, 
Larus scoresbiit Traill).—Procellarus Bonaparte, Naumannia, 1854, 211 (type, by 
original designation, P. neglectus Bonaparte=Larus scoresbit Traill).—Epitelarus 
Bonaparte, Naumannia, 1854, 211 (type, by original designation, EH. [or Procellarus] 
neglectus Bonaparte=Larus scoresbii Traill). 
Southern South America. (Monotypic.) 
5 Gabianus Bruch, Journ. ftir Orn., 1853, 100 (ex Bonaparte, manyscript; type, by 
original designation and monotypy, Larus pacificus Latham). 
Australia and Tasmania. (Monotypic.) 
¢Gelastes Bonaparte, Naumannia, 1854, 212 (type, by tautonymy and original 
designation, G. rubriventris Bonaparte=Larus gedastes Thienemann).—Lambruschinia 
Salvadori, Cat. Ucc. Sardin., Tens 128 (type, by original designation, Larus gelastes 
Thienemann). 
Mediterranean, Caspian, and Red Seas, Persian Gulf, coasts of Africa, ete. (Mono- 
typic.) 
4 Ichthyaetus Kaup, Natiirl. Syst., 1829, 102 (type, by original designation and 
tautonymy, Larus ichthyaetus Pallas). 
Black Sea to India, Ceylon, etc. (Monotypic.) 
