GULLS AND ALLIED SPECIES. 473 



moderate length, flattened beneath ; interdigital membranes 

 slightly emarginate ; claws rather small, compressed, mode- 

 rately arched, rather acute. Wings very long, rather narrow, 

 pointed. Tail of moderate length, even. 



1. Rissa tridactyla. Black-footed Kittiwahe. The only 

 species. White, the back and wings light bluish-grey ; tips 

 of five outer primaries and outer web of first, black. 



GENUS IV. LARUS. GULL. 



Bill of moderate length, stout, straight, compressed, 

 higher near the end than at the base, decurved at the end ; 

 upper mandible with the ridge rather broad, convex, the 

 nostrils medio-basal, linear-oblong, Avider anteriorly, covered 

 above and behind with a sloping thin-edged plate, the edges 

 very thin, direct, the tip narrow, obtuse ; lower mandible 

 much compressed, the lower outline of the crura concave, 

 forming an obtuse angle at the commissure, the dorsal line 

 ascending, somewhat concave, the edges very thin and some- 

 what inflected, the tip narrow, but obtuse. Legs of moderate 

 length, slender ; tibia bare for a short space ; tarsus rather 

 short, somewhat compressed, covered anteriorly with nume- 

 rous, much-curved scutella, laterally with angular scales, 

 posteriorly with numerous small rectangular scales ; hind toe 

 very small, and elevated ; fore toes of moderate length, slen- 

 der ; interdigital membranes with the margin a little concave ; 

 claws small, slightly arcuate, obtuse. Wings very long, 

 rather broad, pointed. Tail rather short, even, or slightly 

 rounded. 



1. Larus marmus. Great Black-hacked Gull. Bill two 

 inches and two-thirds along the ridge, which is much decurved, 

 one inch high at the angle, which is prominent ; tarsus three 

 inches long ; wings slightly surpassing the tail. Bill yellow, 

 with a bright red patch on the lower mandible ; plumage 

 white ; the back and wings greyish-black, tinged with purple ; 

 the quills largely tipped with white. 



2. Larus fuscus. Lesser Black-hacked Gull. Bill two 

 inches along the ridge, eight- twelfths high at the angle, which 

 is moderately prominent ; tarsus two inches and a half long ; 



