XEMA. 37 



GENUS RHODOSTETHIA MACGILLIVRAY. (Page 23, pi. YIL, fig. 3.) 



Species. 



Summer adult : Mantle and under surface of wing uniform pale pearl-gray, the 

 secondaries and innermost quills very broadly tipped with pinkish white, and 

 outer web of first quill chiefly black ; rest of plumage white, usually more or less 

 (sometimes very strongly) tinged with delicate peach-blossom pink, the middle of* 

 the neck encircled by a narrow black collar. Winter adult : Similar, but black col- 

 lar absent, a blackish spot immediately in front of eye, and top of head tinged with 

 pearl-gray. Young, second summer? Similar to summer adult (including collar), but 

 smaller wing-coverts, inner secondaries, primary-coverts, alulae, and adjacent small 

 feathers, together with three outer quills, blackish, the inner web of the latter, how- 

 ever, with marginal half pearl-gray ; remaining quills pearl-gray, becoming white 

 on innermost quills, and all of them tipped with black ; third, fourth, and fifth tail- 

 feathers broadly tipped with black. Young : Back and scapulars heavily spotted 

 or clouded with dusky or sooty blackish, this color prevailing on lower back, where 

 the feathers have buify tips ; top of head and hind-neck also clouded with dusky ; 

 middle tail-feathers with the end sooty black for about .85, the succeeding feathers 

 on each side tipped with black in decreasing extent to the third, which has but a 

 slight mottling of dusky at extreme tip ; wing-coverts dusky, or sooty, tipped with 

 pale buffy; two innermost quills pure white, the rest parti-colored; head, neck, 

 and lower parts chiefly white, marked anteriorly (except on chin and throat) with 

 narrow bars of dusky. Length 11.50-14.00, wing 9.50-10.50, tail 4.00-5.50 (gradu- 

 ated for .75-1.25), culmen .6S-.75, tarsus 1.20-1.25, middle toe 1.00-1.05. Egg 

 (single specimen) 1.90 X 1-30, in color like that of Xema sabinii (fide SEEBOHM. P. 

 Z. S. 1886, 82). Hob. Arctic Ocean, south, in autumn or winter, to northern Alaska, 

 Kamtschatka, Disco Bay, Faroes, Heligoland, and (accidentally) England. 



61. R. rosea (MACGIL.). Ross's Gull. 



GENUS XEMA LEACH. (Page 23, pi. IX., figs. 1, 2.) 



Species. 



a 1 . Culmen much shorter than tarsus ; tail forked for not more than the length of 

 the tarsus ; wing not more than 11.25 ; legs and feet black. (Subgenus 

 Xema?) Summer adult : Head and upper neck uniform plumbeous, bordered 

 below by a black collar ; mantle deep bluish gray ; quills black, the five in- 

 nermost ones varied with white and plumbeous ; rest of plumage white ; bill 

 black, tipped with yellowish. Winter adult: Similar, but head and neck 

 white, except ear-coverts and back of head and neck, which are dull dusky 

 plumbeous. Young : Mantle brownish gray, each feather darker subtermi- 

 nally, and margined at tip with pale fulvous or buffy ; tail white, with a broad 

 black band near end, this again narrowly tipped with white; upper tail- 

 coverts and entire lower parts white. Downy young (fide MIDDENDOBPF) : 



