White-rumped Shrike 431 



this species. He found the nests usually placed in low 

 bushy thick-twigged willows at from seven to twenty 

 feet from the ground. The nest is a bulky, rather untidy 

 structure of grass and other vegetable stems, lined with 

 finer material, including wool and hair. The eggs, 

 seven or eight in number, are whitish-yellow, uniformly 

 freckled with yellowish-brown, and measure about 

 •97 X -72. 



Family VIREONIDiE. 



Bill variable in size, but rather Shrike-like, strong^ 

 hooked and notched ; nostril oval or rounded, overhung 

 by an operculum ; frontal and rictal bristles present ; 

 wing with ten primaries, but the outer or tenth sometimes 

 so small and rudimentary as to be entirely concealed, 

 sometimes about half the length of the ninth ; tarsus 

 longer than the middle toe and claw, scutellate in front ; 

 toes adherent at the base, the basal joint of the middle 

 toe rather shortened and soldered to the basal joints 

 of the lateral toes ; plumage with plain green and grey 

 prevailing ; never spotted or barred even in the young. 



This is a purely New World family, containing the 

 Vireos or Greenlets ; about seventy species are kno^vn ; 

 those of North America were formerly all referred to the 

 type genus, but it is perhaps a matter of convenience 

 to divide them as is here done. 



Key of the Colorado Species. 



A. Tenth primary entirely concealed, apparently absent ; no 



wing-bars. V. olivacea, p. 432. 



B. Tenth primary narrowed, pointed and short, less than } 



length of the ninth. 



a. No wing-bars. V. g. swainsoni, p. 433. 



b. Two distinct pale wing-bars. 



a^ OUve-green above and on the flanks and edges of the 



wing. L. s. cassini, p. 435. 



b^ Grey above.edges of wing whitish. L. s, plumbeus, p. 435. 



