386 Mr. W. A. Forbes on the Structure 



LARUS MARINUS. 



The Great Black-backed Gull is an occasional visitor. It 

 breeds on the Kanin peninsula. 



LARTJS CANUS. 



The Common Gull is a very common summer visitor. 



LARUS BOREALIS. 



The Siberian Herring-Gull (the L. affinis of Reinhardt) is 

 an occasional summer visitor. It breeds in great numbers 

 in the monastery on the island of Solovetsk. Those that 

 cannot find a suitable place outside the monastery breed on 

 the walls and in the court-yard. In the latter alone Henke 

 counted over 500 nests, though the monastery is visited an- 

 nually by about eighty thousand pilgrims. 



STERCORARIUS POMATORHINUS. 



The Pomarine Skua is an occasional visitor. It breeds on 

 the Kanin peninsula. 



STERCORARIUS CREPIDATUS. 



Richardson's Skua is a summer visitor, breeding at the 

 mouth of the Dwina and on the Kanin peninsula. 



STERCORARIUS BUFFONI. 



Buffon's Skua is a summer visitor, breeding at the mouth 

 of the Dwina and on the Kanin peninsula. 



XXVIII. On the Variations from the Normal Structure of 

 the Foot in Birds. By W. A. FORBES, B.A., M.B.O.U., 

 Prosector to the Zoological Society. 



" IN all birds, even in Archceopteryx, the fifth digit of the 

 pes remains undeveloped .... Many birds have only three 

 toes, by suppression of the hallux. In the Ostrich, not only 

 the hallux, but the phalanges of the second digit are sup- 

 pressed .... hence the Ostrich has only two toes." 



" The normal number of the pedal phalanges in birds is 

 (as in ordinary Lacertilia) 2, 3, 4, 5, reckoning from the 

 hallux to the fourth digit. Among the few birds which con- 

 stitute exceptions to the rule are the Swifts, in which the 



