1901.] Allen, Opossums of the Genus Didelphis. 15 I 



Northern specimens have the nails and outer joints of the toes on 

 the hind feet usually white, but the amount of white varies, being 

 often restricted to one or the other of the hind feet, while the 

 opposite one is entirely black, or, in Florida and the Gulf States, 

 both hind feet may be black. The fore feet are always more or 

 less white in northern specimens; in New York and New Jersey 

 examples the toes are often white for their whole length, while at 

 more southern localities, as in Florida and along the Gulf Coast, 

 only the nails and terminal phalanges are white. In Mexican 

 and South American specimens the toes on both fore and hind 

 feet are wholly black. 



Geographical variation in the character of the pelage is strongly 

 marked. The northern animals (D. virginiana and D. v. pigra) 

 have a long, soft, thick coat of woolly underfur, which is whitish 

 basally for about four fifths of its length, only the longer fibres 

 being tipped with black. Over this underfur is a thin covering 

 of long, coarse, more or less bristly white hairs, usually sufficiently 

 abundant to give a whitish coloration to the animal, through 

 which the black apical zone of the underfur is more or less visible, 

 producing a general grizzled effect. The whole head is white 

 except a blackish eye-ring and a very small dusky spot in front of 

 the eye, and a dusky area on the top of the head, terminating 

 about midway between the eyes and the ears. In the tropical forms 

 the pelage is much coarser, the coat of underfur less soft and 

 full, and the black tipping involves about one third of the length 

 of the underfur, which forms a conspicuous element in the su- 

 perficial coloration. The long bristly white hairs, so abundant in 

 the northern animal, are often replaced in the southern forms by 

 bristly black hairs, the animal then being essentially black, a 

 black phase and a gray phase often occurring at the same 

 localities. In other words, the Opossums at many points south 

 of the United States are dichromatic. 



In southern specimens (D. marsupialis and D. karkinophaga, 

 with their respective subspecies) the pure white cheeks alone 

 represent the almost entirely white head of the D. virginiana group 

 of the North. The white color of the cheeks is sharply cut off 

 above by a dark band running from the base of the ear through 

 the eye to the nose; the dark color of the top of the head forms 

 a rather prominent median stripe, while the rest of the upper 



