EGGS OF BRITISH BIRDS. 271 



and often oval, and are usually two or three inches in diameter. 

 The end of the hole is widened and hollowed into a kind of 

 chamber, about six inches in diameter ; and here the nest is 

 formed. It is usually very slight — a mere bed of dry grass, 

 coarse twitch, a few straws, and lined with one or two large 

 feathers. 



The eggs are from four to six in number. They are scarcely 

 so polished as the eggs of the House Martin, but are of as pure a 

 white, and vary in length from 0"76 to 0"62 inch, and in breadth 

 from 0-51 to 046 inch. 



THE PUKPLE MARTIN. 

 (P rogue purpurea.) 



The Purple Martin has a very slender claim to be considered a 

 British bird, but has been believed to have occurred once. It is 

 a summer visitor to the United States and Canada, ranging 

 northwards above the Arctic circle. 



The nest appears to be a very loosely-made structure of dry 

 leaves and grass, fine straws and twigs, and is lined with a con- 

 siderable quantity of feathers. It is placed in the hole of a 

 building, a rock, or a tree. 



The eggs are from four to six in number, pure white and very 

 glossy, and measure from 10 to 0'93 inch in length, and from 0"8 

 to 0"65 inch in breadth. 



FAMILY TETBAONIDJE, 

 OB GROUSE. 



THE COMMON PTAEMIGAN. 

 (Tetrao mutus.)* 

 Plate 59, Figs. 4, 6. 

 The Common Ptarmigan is a bird of the tundra ; and in the 

 British Islands is confined to those moors in Scotland which lie 

 above the limit of forest-growth. It is a circumpolar bird, breed- 

 ing on the tundra of Europe, Asia, and America, above the limit 



* Lagopus mutus — Saunders, Manual, p. 483. 



