250 
LARINiE. RISSA. 
above and behind with a sloping, convex, thin-edged plate, 
the sides beyond the nostrils erect and flattened, the edges 
thin, direct, the tip narrow, rather acute, very slightly pro- 
longed ; lower mandible narrower, compressed, with the in- 
tercrural space long and narrow, the lower outline of the 
crura slightly concave, forming a slight prominence at the 
commissure, the dorsal line distinctly concave and scarcely 
ascending, the edges thin and inflected, the tip compressed 
and rather acute ; the gape-line commencing beneath the 
eyes. Tongue and digestive organs as in the Gulls and 
Mews. Legs very short ; tibia bare to a moderate extent ; 
tarsus very short, considerably compressed, with anterior 
decurved scutella ; hind toe extremely diminutive, with a 
minute claw, which is obsolete in old individuals ; anterior 
toes of moderate length, the shortest as long as the tarsus ; 
webs entire, slightly emarginate ; claws rather small, com- 
pressed, moderately arched, rather acute. Plumage full, 
close, soft ; wings very long, rather narrow, pointed ; tail 
of moderate length, even, of twelve feathers. 
Only one species is known. The genus is intermediate 
between Larus and Cetosparactes. As in the latter, the 
young are spotted with black, but only on the back and 
wings. 
308. Ejssa tridactyla. Kittiwake. 
Bill about an inch and a half in length, five- twelfths high 
at the knob ; tarsus an inch and a quarter long. In winter, 
the bill pale greenish-yellow; feet black; back and wings 
light bluish-grey ; tips of five outer primaries and outer web 
of first black ; the rest of the plumage pure white, except the 
hind part of the neck and the occiput, which are pale bluish- 
grey. In summer, the head and neck pure white, the other- 
parts as in winter. Young with the bill black, the feet 
greenish-grey, forehead and lower parts white, a narrow black 
crescent before the eyes, a dark grey patch over the ears, the 
occiput tinged with grey, a dusky patch on the nape ; the 
back deep greyish-blue ; the feathers margining the wing and 
those along the humerus black; scapulars and secondaries 
with a black patch ; tail white, with a broad black band, not 
including the outer web of the outer feather. 
Male, 17, 36, 12J ; H, If, 1 T %, tV Female, 16£, 35. 
The Kittiwakes arrive along our coasts in the end of April, 
