152 



BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



Sialia mexicana anabelx Anthony, Proc. Cal. Ac. Sci., 2d ser., ii, Oct., 1889, 79 

 (San Pedro Martir Mts., Lower California; coll. A. W. Anthony); Zee, 

 iv, no. 3, 1893, 247, in text under S. mexicana. — Ridgway, Auk, xi, 1894, 

 159 (monogr.); Man. N. Am. Birds, 2d ed., 1896, 613. — American Orni- 

 thologists' Union Committee, Auk, xii, 1895, 166; Check List, 2d ed., 

 1895, no. 7676. 



S\ialia'\ m{ex%cana'\ anabclse Coues, Key N. Am. Birds, 5th ed., i, 1903, 258. 



[8iali(i\ annheJir Sharpe, Hand-list, iv. 1903, 184. 



SIALIA MEXICANA BAIRDI Ridgway. 

 CHESTNUT-BACKED BLUEBIRD. 



Siniilar to S'. m. occidcntalif^ , but adult male with whole back and 

 scapulars uniform chestnut, jiroducing a large and conspicuous 

 dorsal patch; cinnamon-rufous of under parts more extended, 

 alwaj-s extending broadly across chest, sometimes covering whole 

 breast; adult feiriale witli upper parts browner than in S. m. occi- 

 dentalis, the back and scapulars hair l)row"n to betw^een sepia and 

 prouts brown, usually in strong and abrupt contrast w4th the mouse 

 gray or hair brown of pileum and hindneck; young much darker 

 and browner than those of ^S*. m. occidentalis or *S'. m. anahelsr, with 

 under parts more heavily streaked or squamated and the streaked 

 areas more or less strongly suffused with pale fulvous or rusty brown- 

 ish. Decidedly larger than aS'. m. occidentalis, with smaller bill. 



Adult 77m?/.— Length (skins), 149-171 (161); wing, 105-117 

 (110.7); tail, 03.5-71 (67.9); exposed culmen, 11-13 (12); tarsus, 

 19-21.5 (20.2); middle toe, 14-16 (14.9).° 



Adult female.— I^ength (skins), 141-171 (154); wing, 101.5-109.5 

 (105.4) ;" tail, 58-68 (63.5); exposed culmen, 11-13 (12.1); tarsus, 

 18.5-20.5 (19.5); middle toe, 13.5-15 (14.1).^ 



a Twenty-one specimens. 



b Eighteen specimens. • 



Specimens from the United States compare in average measurements with breeding 

 examples from northwestern Mexico as follows: The two series are essentially alike 

 in color, but the adult males from Mexico all have the whole dorsal regipn "solid" 

 chestnut, or rufous-chestnut, and the females are slightly darker in general coloration. 

 In short, the form reaches its most perfect development, with characters more accen- 

 tuated and stable, in northwestern Mexico. 



