3 
Mr. R. Ridgway on the Genus Micrastur. 
termed by Pelzeln “ erythrism,” and entirely analogous to 
the condition of melanism. The condition is most exaggerated 
in M. ruficollis, but it is plainly visible in M. guerilla. No 
rufous specimens have been seen of M, concentricus, Pelz., nor 
M. pelzelni ; and, on the other hand,, I have seen no plumbeous 
examples of M. zonothorax. But such probably occur, and 
should be borne in mind before any new form is described. 
Synopsis of the Species of Micrastur. 
A. Outer toe decidedly longer than the inner. 
a. Size large (wing more than 8 inches). 
1. Above black, with a nuchal collar of white or ochraceous. 
M. melanoleucus*. 
2. Above plumbeous, without a nuchal collar . . M. mirandollii. 
b. Size small (wing less than 8 inches). 
3. Wing 6-50-7T0, tail 6-90-7-50. Tail crossed by 3-6 (terminal 
bar not counted) indistinct bars of white or pale greyish. Adult. 
Tail-bars 3-4; above plumbeous, the dorsal region sometimes 
chocolate; throat light grey; jugulum, breast, and entire lower 
parts barred with white and dusky. Young . Above dark clove- 
brown, plain or indistinctly spotted posteriorly; beneath white 
or buff, rarely immaculate, usually coarsely barred. 
M. guerilla. 
4. Wing 6-90-7'oO, tail 7‘60-8”40. Tail with 4-7 distinct white 
bars. Adult. Above, including neck and most of head, rusty 
chocolate, less reddish anteriorly; throat light chocolate; jugu¬ 
lum and entire lower parts everywhere barred with white and 
dusky. Tail-bands 4-5. Young. Above dark sooty brown, in¬ 
distinctly barred with rusty; crown and nape sooty black; lower 
parts white or buff, rarely immaculate, usually barred, and with¬ 
out rufous tinge on the breast; tail-bars 6-7. M. zonothorax. 
5. Wing 6-60-7T0, tail 7‘30-7-80. Tail with 4-8 usually distinct 
white bars. Adult. Breast washed with rufous; throat light 
grey; other lower parts everywhere barred with white and 
dusky; crown plumbeous ; other upper parts varying from clear 
light bluish plumbeous to rusty brown. Tail-bars 4. Young. 
Above varying from greyish brown to dark rusty chocolate; 
throat and half-crescent behind the ear-coverts white, in abrupt 
contrast; beneath white, coarsely barred with dusky brown 
M. ruficollis. 
* I cannot identify Sparvius semitorquatus, Vieill., with this species, 
since that is said to have the top of the head white, barred with black, 
whereas it is always plain black in this bird, which, in the adult plumage 
is S. melanoleucus, Vieill. 
B 2 
