738 BULLETIN 50, TJITITED STATES NATIONAL MUSEUM. 



minate, and it is more for convenient identification of specimens than 

 for any other reason that extreme subdivision has been made. The 

 only case which affords an exact parallel to the present one, so far as 

 groups treated in the present and prior volumes of this work are con- 

 cerned, is that of Ghordeiles virginianus, the geographic variations of 

 which are treated in a similar manner. 



The measurements are those pubHshed by Mr. Oberholser, it having 

 been deemed inexpedient and quite unnecessary to dupHcate the 

 labor involved in making them. 



KEY TO THE SUBSPECIES OF BUBO VIRGINIANUS." 



a. Wing averaging not less than 350 mm. (usually much more) in females, not less 

 than 335 mm. in males. 

 6. Wing averaging less than 365 mm. in females, less than 345 mm. in males. 

 c. Upper parts darker, dusky or dark grayish brown predominating. 

 d. Wing averaging more than 360 mm. ; with much rufous or tawny in plumage. 

 (Eastern United States and southern Canada, west to eastern border of 



Great Plains.) Bubo virginianus virginianus (p. 739). 



dd. Wing averaging less than 360 mm.; with little it any rufous or tawny in 

 plumage, 

 e. More blackish above; feet slightly mottled. (Western Ecuador.) 



Bubo virginianus nigrescens (extralimital).^ 

 ee. Less blackish above; feet conspicuously mottled. (Coast district of 

 California, from about 35° N. lat., to San Francisco Bay.) 



Bubo virginianus icelus (p. 746). 



cc. Upper parts lighter, grayish brown and buffy predominating. 



d. Face and under parts darker, the feet more spotted. (California, except 



coast district north of 35° and Colorado Desert area; and northwestern 



Lower California, north to central-southern Oregon, oast to San Francisco 



Mts., Arizona.) Bubo virginianus pacificns (p. 745). 



dd. Face and imder parts paler, the feet less spotted, often immaculate. (Cen- 

 tral Texas to southeastern California; northern Mexico.) 



Bubo virginianus pallescens (p. 742). 

 65. Wing averaging more than 371 mm. in females, more than 348 mm. in males. 

 c. Light colored. 

 d. Darker (white not predominating); feet more or less mottled or spotted, 

 e. Lighter above, the under parts less heavily barred. (Central North Amer- 

 ica, from Minnesota, Kansas, etc., to Nevada, southeastern Oregon, etc., 

 north to southern Assiniboia and Manitoba, south to Nevada, Utah, 

 northern New Mexico, and Kansas.) 



Bubo virginianus occidentalis (p. 743). 



o Based chiefly on adult females. Unfortunately, the characters distinguishing 

 the several forms being pmrely comparative and the measurements often overlapping 

 on account of sexual difference in size (the females of any form being always larger 

 than the males), an entirely satisfactory "key" is probably impracticable. Indeed, 

 the difficulty is increased by the circumstance that many of the forms are more or less 

 dichromatic or even polychromatic, that is to say, have two or more different individual 

 phases of coloration, and thus there is an "overlapping," to a greater or less extent, 

 in color as well as in dimensions. 



6 Bubo nigrescens Berlepsch, Proc. Zool. Soc. Lond., 1884, 309 (Ceche, 10,000 ft., 

 w. Ecuador; coll. Warsaw Mus.). — Asio magellanicus nigrescens Oberholser, Proc. 

 U. S. Nat. Mus., xxvii, no. 1352, Jan. 22, 1904, 179 (monogr.). 



