129. Sterna (Other Terns). Outer tail feathers longest, pointed; tarsus short; tail at least half length of wing; bill compressed and slender; tarsus never exceeds length of middle toe with claw.
SUB-FAMILY LARINÆ
Bill with upper mandible longer and bent over tip of under one.
130. Larus (Gull). Bill moderate, strong, sharp-edged above, compressed, slightly decurved; hind toe high on the tarsus; first primary nearly equal to the second, which is longest; tail even, or but slightly forked.
131. Rissa (Kittiwake). Bill rather short and stout, considerably decurved; hind toe minute and usually obsolete; first primary slightly exceeding second; tail perceptibly forked in young, nearly square in adult.