42 Bulletin American Museum of Natural History. [Vol. XX, 



(front of incisors to posterior border of condyles), 69; height at con- 

 dyle, 38; height at coronoid process, same as at condyle; length of 

 lower premolar-molar series, 27.5. 



Adults of the same sex present a rather wide range of variation in 

 color, wholly independent of sex or age. In the darkest specimens the 

 head, neck, limbs, and tail are deep black; the shoulders and dorsal 

 region are brownish black, the black being less intense and slightly 

 suffused with a ruddy cast, becoming still paler and lighter on the pos- 

 terior half of the dorsal region, especially on the loins, where the suffu- 

 sion is paler and more yellowish; a narrow lateral line of dark yellowish 

 rufous runs from the shoulders to the thighs ; ventral surface yellowish 

 gray, which color extends in a narrow line down the inside of the 

 upper arm to the elbow, and down the inside of the thighs to a little 

 below the knee, narrowing distally. 



In the lightest examples the head, distal half of the limbs, and tail 

 are dull black; the nape, shoulders, and the proximal half of the limbs 

 and tail brownish black, with a strong dull yellowish red suffusion; the 

 dorsal area posterior to the shoulders is dingy golden yellow, brighten- 

 ing on the sides to brilliant golden rufous, terminating abruptly 

 against the lighter color of the ventral surface in a sharply limited 

 lateral line of deep golden rufous, which is prolonged posteriorly over 

 the upper part of the thighs and down the inner side of the hind legs 

 to below the knees; ventral surface clear yellowish white. Between 

 these is every stage of gradation. 



In the lighter-colored specimens there is a striking similarity in the 

 tints and in the pattern of coloration to Alouatta palliata mexicana, 

 which occurs abundantly with it at Pasa Nueva, but the darker under 

 surface of the latter readily distinguishes the two species without 

 resort to other characters. 



The single very young specimen in first pelage is very thinly haired, 

 the ventral area being practically naked. The whole dorsal area, 

 limbs, and tail are uniform blackish. 



The type of Ateles vellerosus Gray (P. Z. S., 1865, p. 733; 

 Cat. Monkeys, etc., 1870, p. 44) was supposed by the describer 

 to have come from Brazil, but later Alston (Biol. Centr.-Am., 

 Mamm., 1879, p. 10) considered it identical with specimens 

 from Central America. In the meantime Sclater figured under 

 this name (P. Z. S., 1872, p. 4, pi. ii) a specimen believed to 

 have been procured near Acapulco, Mexico, which he con- 

 sidered as indistinguishable from Gray's type. The authen- 

 ticity of this locality was soon after questioned by Reinhardt 

 (P. Z. S., 1872, p. 797), who, however, referred specimens to 

 vellerosus from Mirador, Vera Cruz, "although the yellowish 



