408 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
aa. Chin and throat white. 
b. Sides of neck without metallic blue; tail bronzy olive to coppery bronze. 
c. Sides of neck mostly white; under tail-coverts white, and under parts of body 
almost wholly white. 
d. Forehead and crown dusky greenish or dull bluish. (Southwestern Mexico.) 
Amizilis viridifrons (p. 421). 
dd. Forehead and crown bright metallic blue or violet. 
e. Tail dull greenish bronze. (Western Mexico.) 
Amizilis verticalis (p. 422). 
ee. Tail bronze to coppery bronze. (Southwestern Mexico.) 
Amizilis violiceps (p. 424). 
cc. Sides of neck metallic green; under tail-coverts dull olive-bronze to coppery 
bronze margined with white; under parts of body with only the median 
line white. 
d. Bill larger (culmen 18.5-23); tail, sides, flanks, and under tail-coverts more 
greenish or olive bronze. (Amizilis cyanocephala.) 
e. Tail duller bronzy, the rump and upper tail-coverts more faintly glossed 
with bronze. (Southeastern Mexico, including State of Chiapas.) 
Amizilis cyanocephala cyanocephala (p. 425). 
ee. Tail brighter bronzy, the rump and upper tail-coverts more strongly 
glossed with bronze. (Guatemala, Honduras, and British Honduras.) 
Amizilis cyanocephala guatemalensis (p. 427). 
dd. Bill smaller (culmen 13.5); tail, sides, flanks, and under tail-coverts more 
coppery bronze. (Honduras?).......... Amizilis microrhyncha (p. 428). 
bb. Sides of neck metallic blue; tail dark metallic green or bronze-green. (North- 
western Mexico and southern Arizona.).....-.-..-- Amizilis salvini (p. 429). 
AMIZILIS TZACATL TZACATL (De la Llave). 
RIEFFER’S HUMMING BIRD. 
Adult male-—Above metallic bronze-green or greenish bronze, the 
pileum darker and duller; upper tail-coverts and tail chestnut, the 
rectrices margined terminally with dusky bronze, the coverts some- 
times partly bronze or bronze-green; remiges dusky, faintly glossed 
with violet; lores chestnut; malar region, chin, throat, chest, upper 
breast, and sides of lower breast bright metallic yellowish emerald- 
green, the feathers of chin and upper throat pale buff or buffy white 
basally, this much exposed on chin; abdomen and median portion of 
lower breast brownish gray; sides and flanks bronze-green; under 
tail-coverts cinnamon-rufous; femoral tufts white; bill brownish 
(reddish in life), dusky terminally, the maxilla sometimes mostly 
(rarely wholly?) blackish; iris dark brown; feet dusky (in dried 
skins); length (skins), 86-105 (97); wing, 46-61 (58.3); tail, 29.5-35 
(32.8); culmen, 18-23 (20.8).% 
Adult female.—Similar to the adult male and perhaps not always 
distinguishable, but usually with the green of under parts more 
broken by whitish margins to the feathers, gray of abdomen paler, 
and cinnamon-rufous loral streak less distinct, sometimes obsolete; 
4 Sixty specimens. 
