I 76 Bulletin American Museum of Natural History. [Vol. XIV, 



the dull greenish orange-buff color of the basal portion of the 

 underfur; also in the very strongly denned median black stripe 

 running over the top of the head from a point a little in front of 

 the eyes to the occiput, and in the nape and shoulders being 

 nearly black in contrast with the rest of the dorsal surface, the 

 coarse overhair being almost wholly black on the anterior portion 

 of the body and mainly whitish on the posterior. The amount 

 of black at the base of the tail varies from about one third to two 

 thirds of the total length of the tail. The ratio of tail length to 

 the length of head and body averages, in the three adult speci- 

 mens, 112, while the ratio of the length of the nasals to the basal 

 length of the skull is 53.5. 



In short, D. richmondi is much more closely related to the D. 

 karkinophaga group than to D. marsupialis, sharing with the mem- 

 bers of the karkinophaga group the dingy orange-buff color at the 

 base of the underfur. In general features D. richmondi most 

 closely resembles D. k. caucce from the upper Cauca Valley of 

 western Colombia, but differs from this form in its much larger 

 size and slenderer form, the relative length of the nasals and tail 

 in D. cauca being nearly the same as in D. marsupialis. 



NOTE ON Didelphis pernigra. 



In this connection it may be added that the distinctness of D. 

 pernigra from all other forms of Didelphis is emphasized by this 

 further study of the group, its distinctive features being, as 

 already stated, its small size, very long tail, peculiar coloration 

 and pelage. The black overhair of the pelage in D. pernigra is 

 less stiffened than in the other forms of Didelphis and hardly 

 corresponds in coarseness and harshness to the overhair in the 

 other forms of the genus. To emphasize its differences in size 

 and proportions, a table of measurements (see Table VI) and 

 also illustrations (PI. XXIV, Figs, i-ia) are added for compari- 

 son with the other forms. 



It has also become evident that dichromatism prevails in the 

 various forms of the D. karkinophaga group, at least so far as 

 those of northern South America are concerned, though not be- 

 fore recognized. It occurs in the Trinidad form, provisionally 

 taken to represent D. karkinophaga, in the absence of satisfac- 

 tory material from Guiana; it occurs also in D. k. colombica^ 



