ALOUATTA 259 



The majority of the species are black or partly so, although six are 

 clothed in fur exhibiting shades varying from straw color to dark red. 

 In some species the sexes are alike in color, in others quite different, 

 and the young of some resemble their parents, while those of others 

 are totally unlike the adults, and they can therefore be arranged in two 

 groups. The fur is short on the bodies of some species, quite long on 

 others, but is usually thickest on the head. 



Wallace (1. c.) writing of the Howling Monkeys, under the genus 

 Mycetes, on the Lower Amazon, states that they are generally abun- 

 dant; the different species, however, are found in separate localities, 

 (M.) beelzebul being confined apparently to the Lower Amazon in 

 the vicinity of Para; a black species, (M.) caraya to the Upper 

 Amazon, and a red species, (M.) ursina to the Rio Negro and Upper 

 Amazon. Much confusion seems to exist with regard to the species 

 of Howlers, owing to the difference of color in the sexes of some 

 species. The red and black species of the Amazon, however, are of the 

 same color in both sexes. These animals are semi-nocturnal in their 

 habits, uttering their cries late in the evening and before sunrise, and 

 also on the approach of rain. Humboldt observes that the tremendous 

 noise they make can only be accounted for by the great number of 

 individuals that unite in its production. His own observations, and the 

 unanimous testimony of the Indians, prove this not to be the case. One 

 individual only makes the howling, which is certainly of a remarkable 

 depth and volume and curiously modulated, but on closely remarking 

 the suddenness with which it ceases and again commences, it is evi- 

 dent that it is produced by one animal, which is generally a full grown 

 male. On dissecting the throat, much of our wonder ceases, for 

 besides the bony vessel formed by the expansion of the "Os hyoides," 

 there is a strong muscular apparatus which seems to act as a bellows in 

 forcing a body of air through the reverberating bony cavity. 



LITERATURE OF THE SPECIES. 



1766. Linnceus, Sy sterna Natures. 



Alouatta beelzebul first described as Simla beelzebul; and A. 



sericulus first described as Simla serlculus from Cartagena, 



Colombia. 

 1777. Erxleben, Systema Regnl Anlmalls. 



The two species described by Linnaeus are here placed in the 



genus Cebus. 



