BIRDS OF NORTH AND MIDDLE AMERICA. 563 



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. 



Leucophseus (extralimital).« 



(Id. 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).'' 



et. Bill 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 less than half the distance from anterior end of nostril 



to tip of maxilla Gelastes (extralimital). c 



ff. Bill shorter or stouter (or both), the exposed culmen shorter than 

 middle toe with claw, its length from rictus shorter than tarsus, ita 

 greatest depth more than half the distance from nostril to tip of 

 maxilla. 

 g. Adults with under parts wholly white, young -wdth 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 wdng-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 v,-hiti.-h 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 Ichthyaetus (extralimital).-** 



<^ Leucophaeus Bruch, Journ. fiir Orn., 1853, 108 (type, by original designation, 

 Larus scoresbii Traill). — Procellarus Bonaparte, Naumannia, 3854, 211 (type, by 

 original designation, P. neglectus Bonaparte=L«nis scoresbii Traill). — Epitclarua 

 Bonaparte, Naumannia, 1854, 211 (type, by original designation, E. [or Procellarus] 

 neglectus Bonaparte = Larus scoresbii Traill). 



Southern South America. (Monotypic.) 



^Gabianus Bruch, Journ. fiir Orn., 1853, 100 (ex Bonaparte, manuscript; type, by 

 original designation and monotypy, Larus pacijicus Latham). 



Australia and Tasmania. (Monotypic.) 



<' Gelastes Bonaparte, Naumannia, 1854, 212 (type, by tautonymy and original 

 designation, G. rubriventris Jionsiimrte= Larus gelastes Thienemann). — Lambruschinia 

 Salvadori, Cat. Ucc. Sardin., 1864, 128 (type, by original designation, Larus gelastest 

 Thienemann). 



Mediterranean, Caspian, and Red Seas. Persian Gulf, coasts of Africa, etc. (Mono- 

 typic.) 



<i Ichthyaetus Kaup, Natiirl. Syst., 1829, 102 (type, l)y original designation and 

 tautonymy, Larus ichthyaetus Pallas). 



Black Sea to India, Ceylon, etc. (Monotypic.) 



