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



Marta forms, either geographically or otherwise, the Cauca 

 subspecies may be provisionally distinguished as follows: 



Alouatta seniculus caucensis, subsp. nov. 



Type, No. 14162, $ ad., Charingo (alt. 3000 ft.), upper Cauca 

 Valley, Colombia, May 5, 1898; coll. J. H. Batty. 



Head, neck, limbs and tail dark reddish chestnut, the latter much 

 paler apically than at the base ; back and sides golden yellow, deepen- 

 ing to orange yellow on flanks ; pectoral region naked, ventral surface 

 thinly clothed with reddish hairs. Total length, 1234; head and 

 body, 603; tail vertebrae, 640; hind foot, 135; ear, 35. Skull, total 

 length, 116; zygomatic breadth, 80. (For further measurements see 

 table below.) The type has the largest external measurements of 

 the series, but not the largest cranial measurements. Three adult 

 males average, total length, 1155; tail vertebrae, 600; skulls of the 

 same, total length, 119; zygomatic breadth, 77.5. 



There is considerable variation in color, the brightest specimens 

 closely approaching the faded specimens of the Santa Marta series. 

 The two series, as a whole, however, differ strikingly in coloration, as 

 indicated above. 



Alouatta seniculus caucensis averages much less in external 

 measurements than A. s. rubiginosa, and it has also a con- 

 siderably smaller skull, but the most marked differences are 

 in the cranial details. In caucensis the skull is narrower and 

 flatter, the zygomata are much less expanded, the palatal re- 

 gion much narrower, and the rostral portion of the skull is 

 much compressed, with correspondingly narrower nasals. 

 Thus the nasals in caucensis have an average breadth at the 

 front border of 10 mm. against 14 in rubiginosa, with the 

 necessarily correlated difference in contour of the nasal 

 region this implies, the least interorbital breadth being 2.5 

 mm. less in caucensis. In rubiginosa the upper toothrows in 

 old males are often curved slightly outward and the palatal 

 area is very broad; in caucensis the upper toothrows are 

 straight and parallel, and the palatal area is much narrower, 

 the distance between m 1 in the two forms being, respectively, 

 24.6 (10 males) and 21.8 (5 males). (See figs. 3 and 4.) 



The following tables of measurements show the difference 

 in size in the two forms and in cranial proportions. (The 



