214 BONAPARTIAN GULL. 
had frequent opportunities of seeing the black-hooded males copulating 
with the brown-hooded females, so that the colour of the head in the 
summer season is really distinctive of the sexes. I found in London a 
pair of these birds, of which the sexes were distinguished by the co- 
lour of the head, and which had been brought from Greenland. They 
were forwarded by me to the Earu of Dersy, in whose aviaries they 
are probably still to be seen. 
This is certainly the species described in the Fauna Boreali-Ame- 
ricana under the same name; but it is there stated that the females 
agree precisely with the males, their hood being therefore ‘“ greyish- 
black ;” which I have never found to be the case. As to the Larus 
capistratus of Bonaparte’s Synopsis, I have nowhere met with a Brown- 
headed Gull having the tail ‘‘ sub-emarginate ;” and I infer that the bird 
described by him under that name is merely the female of the present 
species. 
Larus Bonapartil, BonaPaRTIAN GULL, Richards. and Swains. Fauna Bor.-Amer. 
vol. ii. p. 425. 
Brown-mMaskED Gutt, Larus capistratus, Bonap. Amer. Ornith., vol. iv. 
Female. 
Larus caPistratTus, Oh. Bonaparte, Synopsis of Birds of United States, p. 358. 
Bonapartian Guux, Wuttall, Manual, vol. ii. p. 294. 
Adult Male in Spring Plumage. Plate CCCXXIV. Fig. 1. 
Bill shorter than the head, nearly straight, slender, compressed. 
Upper mandible with its dorsal line straight to the middle, then curved 
and declinate, the ridge narrow, the sides slightly convex, the edges 
sharp and a little inflected, the tips narrow but rather obtuse, with a 
slight notch on each side. Nasal groove rather long and narrow; nos- 
trils in its fore part, longitudinal, submedial, linear, pervious. Lower 
mandible with a slight prominence at the end of the angle, which is 
long and narrow, the dorsal line then ascending and slightly concave, 
‘the ridge convex, the sides nearly erect and flattened. 
Head of moderate size, ovate, narrowed anteriorly, convex above. 
Eyes of moderate size. Neck rather short. Body rather slender. 
Wings very long. Feet of moderate length, rather strong ; tibia bare 
below for a short space, covered behind with narrow scutella; tarsus 
compressed, anteriorly covered with numerous scutella and three in- 
