THE HOATZINS. 257 



II. THE BLACK-BREASTED SICKLE-WINGED GUAN. 

 CHAM/EPETES UNICOLOR. 



ChamcBpetes umcolor, 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 black, glossed 

 with dark green ; under-parts similar, but browner on the 

 belly, and generally indistinctly mottled with pale rufous-buff. 

 Total length, 25 inches; wmg, 11 to 117 ; tail, io"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 Gallina volcanica has, up to 

 the present time, only been obtained on the slopes of Irazu, 

 where it is very common, especially near Rancho Redondo 

 and La Raima. 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 sui generis, or approaches the Musophagid<z.^^ The 

 latter group, known as the Touracous, and the Cuckoos 

 [CucuIidcK), are, according to the late Professor Garrod, 

 nearly allied. 



12 S 



