TETRA ONIB^ — TETBA ONIN^ : GB USE. 



687 



secreting part of the passage is as if covered with fresh paint, soft and sticky, which may be. 

 rubbed off before it " sets '" on the shell. Size 1.80 X 1-20. 

 569. li. rupes'tris. (Lat. rv/pestris, relating to rwpis, a rock; rupestrine.) Rock Ptarmigan. 

 BUI slenderer for its length than that of L. albus, its depth at base less than the distance from 

 nasal fossa to tip; whole culmen 0.67; bill always black. $ 9, in winter: As in i. albus, 

 but a black transocular stripe on side of head. ^ $ , in summer : The whole plumage, excepting 

 the wings and tail, barred with blackish-brown and brownish-yeUow. Rather smaller than the 



Fig. 404 —Willow Ptarmigan, winter plumage, J nat. size. (From Brebm.) 



foregoing. Length 14.00-15.00 ; wing 7-00-7.50 ; tail 4.50. Arctic America, not S. to the 

 U. S. Eggs 13-15 or more, like those of L. albus, but darker and rather smaller ; size 

 1.70 X 1-18. "The summer plumage is assumed at variable periods of the months of April, 

 May, and even in early June, according to the locality. The moult for the summer is usually 

 shown first on the head and neck, followed by the lower back, sides, breast, middle back, flanks, 

 and abdomen, in the order named. The abdomen and chin are the last areas to show the com- 

 plete moult. The parts named also assume, in the order given, the white winter plumage. 

 During the time of the summer plumage scarcely a single day passes that the general color of 

 the feathers is not modified by the appearance or loss of some feather." (Turner.) Hence the 

 diflBculty if not impossibility of establishing races of this species upon color, as the amount of 

 barring, vermieulation, or nebulation with dusky, tawny, and gray is incessantly changing in 



