=631c. Small White-eyed Vireo= (_V. n. micrus_). Smaller than No. 631, W. 2.2; averaging grayer above; sides with less yellow.
Range.--Northeastern Mexico, north to southeastern Texas.
=629. Blue-headed Vireo= (_Vireo solitarius_). L. 5.5; W. 2.9; B. .4. _Ads._ Lores and eye-ring white; crown and cheeks bluish slate-color; back olive-green; below white, sides washed with greenish yellow; two whitish wing-bars. _Notes._ Resembling in form those of Red-eyed or Yellow-throated Vireos but more varied, sometimes a continuous warble; a musical chatter, like that of the Yellow-throated and a trilled whistle. (Torrey.)
Range.--Eastern North America; breeds from Connecticut (and south along Alleghanies) north to New Brunswick and Manitoba; winters from Florida to Central America.
=629a. Cassin Vireo= (_V. s. cassini_). Like No. 629, but back washed with the color of the head; white on breast and throat less pure.
Range.--"Breeds from British Columbia and Idaho south along Pacific coast region and Nevada to Lower California; migrates to Arizona, New Mexico; and northern Mexico." (Bailey.)
=629b. Plumbeous Vireo= (_V. s. plumbeus_). Above wholly plumbeous-gray with scarcely, if any, olive tinge, below white, the sides gray _faintly_ tinged with greenish yellow; size of No. 629c.
Range.--Rocky Mountain region; breeds from northern Mexico north to southwestern Dakota and Wyoming; winters south to southern Mexico.
=629c. Mountain Solitary Vireo= (_V. s. alticola_). Larger than No. 629, W. 3.15, B. .46; head darker, its color extending over most of the back.
Range.--Breeds in Alleghanies from North Carolina to Georgia; winters in Florida.
=629d. St. Lucas Solitary Vireo= (_V. s. lucasanus_). Smaller than No. 629a, but bill longer and stouter, sides and flanks much yellower; young without brownish below, and resembling young of No. 629.
=633. Bell Vireo= (_Vireo bellii_). L. 5. Above olive-green, crown grayer; lores and eye-ring white; two inconspicuous whitish wing-bars; below white, sides tinged with yellowish. Most like No. 627, but back greener, no white line _back_ of eye. _Notes._ Resemble those of the White-eyed Vireo, but less harsh, song less emphatic. (Goss.)
Range.--Interior states from Illinois west to Plains; breeds from Texas to Minnesota; winters in Mexico.