THE HOATZINS. 257 
II. THE BLACK-BREASTED SICKLE-WINGED GUAN. 
CHAMEPETES UNICOLOR. 
Chamepetes unicolor, Salvin, P. Z. S. 1867, pp. 159, 160; 
Ogilvie-Grant, Cat. B. Brit. Mus. xxii. p. 522 (1893). 
Adult Male and Female—General colour above Jd/ack, glossed 
with dark green; under-parts similar, but browner on the 
belly, and generally indistinctly mottled with pale rufous-buff. 
Motal length, 25 inches; wig, rr to 11°7 ; tail, 1o0°5\> tarsus, 
2°7; middle toe and claw, 2°85. 
Range.—Central America; Costa Rica and Veragua. 
Habits.—The following note is taken from Dr. v. Frantzius’ 
paper (‘‘ Journal fur Ornithologie,” 1869, p. 372):—‘ This 
species, locally known as the Gad/ina volcanica has, up to 
the present time, only been obtained on the slopes of Irazu, 
where it 1s very common, especially near Rancho Redondo 
and La Palma. It is often brought into the towns to be sold, 
and is most frequently shot at the end of the rainy season, 
as it then leaves the thick forests on the hills and visits the 
lower-lying and less densely-wooded parts.” 
THE HOATZINS. ORDER OPISTHOCOMI. 
Although only a single species comprises this Order, the 
structure of the skeleton presents so many important peculiari- 
ties that the Hoatzin can only be placed in an isolated posi- 
tion. The modifications of the alimentary tract are almost as 
remarkable as the skeletal characters. 
With regard to the latter, Professor Huxley says that it 
“resembles the ordinary gallinaceous birds and pigeons more 
than it does any others, and when it diverges from them it is 
either swz generis, or approaches the MMusophagide.” The 
latter group, known as the Touracous, and the Cuckoos 
(Cuculide), are, according to the late Professor Garrod, 
nearly allied. 
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