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the weather. They are often seen about the Laguna de la Janda, 

 where, in February, 1892, Verner reports seeing vast numbers and 

 caught two alive so gorged with black worms as to be unable to 

 fly. He examined one and found a round mass of these worms, 

 of the size of a golf-ball, in its throat. 



Hind toe absent or rudimentary. 



In summer. Head, neck, and tail pure white ; bill greenish yellow. 

 In winter. Head and neck slate-grey. 



Young. Bill black; brown feathers on back; tail with black band at end. 

 Length 15 inches. 



Subfamily STERCORARIIN.E. ROBBER-GULLS. 



Base of upper mandible covered with a cere or skin, and 

 hooked at the point. 



349. Stercorarius catarractes (Linnseus). The Great Skua. 

 Favier records a single specimen obtained near Tangier, in 



December, 1852. It occurs regularly, but not commonly, during 

 winter in the Straits. 



General colour above dark brown; below lighter brown; axillaries dark 

 brown; primaries blackish brown, bases white, forming a well-marked 

 band. Tail dark brown, white at the base, but this is hidden by the 

 coverts; two centre feathers very slightly longer than the others. Length 

 24-25 inches, leg 2f-3. 



350. Stercorarius pomatorhinus (Temminck). The Twist- 



tailed or Pomatorhine Skua. 



Stated by Favier to be very rare near Tangier ; and he only 

 mentions one specimen, obtained as far back as November, 1845. 

 Is recorded from Malaga. 



Two forms or races are found, both dark brown above. The dark form 

 as dark below as above; the light form white below, barred on flanks and 

 tail-coverts with dark brown, white on the throat, tinged with golden 

 yellow, and sometimes extending round nape. 



Two centre tail-feathers 4 inches longer than the others, and twisted 

 upwards. 



