182 THE GREAT BLACK-BACKED GULL. 



Adult Male in summer. 



Bill shorter than the head, robust, compressed, higher near the end than 

 at the base. Upper mandible with the dorsal line nearly straight at the base, 

 declinate and arched towards the end, the ridge convex, the sides slightly 

 convex, the edges sharp, inflected, arcuate-declinate towards the end, the tip 

 rather obtuse. Nasal groove rather long and narrow; nostril in its fore 

 part, lateral, longitudinal, linear, wider anteriorly, pervious. Lower mandi- 

 ble with the angle long and narrow, the outline of the crura rather concave, 

 as is that of the remaining part of the mandible, a prominent angle being 

 formed at their meeting, the sides nearly flat, the edges sharp and inflected. 



Head rather large, oblong, narrowed anteriorly. Neck of moderate 

 length, strong. Body full. Wings long. Feet of moderate length, rather 

 slender; tibia bare below; tarsus somewhat compressed, covered anteriorly 

 with numerous scutella, laterally with angular scales, behind with numerous 

 small oblong scales; hind toe very small and elevated, the fore toes of 

 moderate length, rather slender, the fourth longer than the second, the third 

 longest, all scutellate above, and connected by reticulated entire membranes, 

 the lateral toes margined externally with a narrow membrane. Claws small, 

 slightly arched, depressed, rounded, that of middle toe with an expanded 

 inner margin. 



The plumage in general is close, full, elastic, very soft and blended, on 

 the back rather compact. Wings very long, broad, acute, the first quill 

 longest, the second scarcely shorter, the rest of the primaries rather rapidly 

 graduated; secondaries broad and rounded, the inner narrower. Tail of 

 moderate length, even, of twelve rounded feathers. 



Bill gamboge-yellow, the lower mandible bright carmine towards the end. 

 Edges of eyelids bright carmine, iris silvery. Feet yellow, claws black. 

 The head, neck, and all the lower parts, pure white; back and wings deep 

 blackish-grey tinged with purple, or dark slate-colour; the rump and tail 

 white, as are the edges of the wing, and a large portion of the extremities of 

 all the quills; the second, third, fourth, and fifth primaries have a broad band 

 of black across their ends, the inner web only of the second being so marked, 

 in some specimens however both webs. The oesophagus is very large, the 

 gizzard small, the intestine four feet long, and about the thickness of a goose 

 quill. 



Length to end of tail 29f inches, to end of wings 31^, to end of claws 

 29i; extent of wings 67; wing from flexure 20; tail 9; bill along the ridge 

 2j§, along the edge of lower mandible 3^; its depth at the .angle 1, at the 

 base i|; tarsus 3 T ? 2 -; middle toe 2\, its claw % Weight 3 lbs. 



The Female is similar to the male, hut considerably less. 



The Young, when fledged, have the bill brownish-black, the iris dark 



