1901.] Allen, Opossums of the Genus Didelphis. 



of the underfur showing through the long overhair ; the white basal portion of the 

 underfur also shows through the blackish surface of the underfur ; ventral sur- 

 face white with a slight wash of dusky formed by the blackish tips of the hairs. 

 There is generally a large pectoral area in adult males suffused with sulphur 

 yellow, varying from a faint shade of this tint to quite strong greenish yellow, 

 and varying also in respect to the size of the area. This pectoral spot is gen- 

 erally absent in young males and apparently always absent in the females. The 

 fur over this area is often saturated with an oily, highly odorous secretion from 

 underlying sebaceous glands, which are probably especially active during the 

 breeding season. There is often a median ventral line of clear white, in both 

 males and females, extending from the breast posteriorly, irregular in outline 

 and extent in different specimens. Whole head, including the throat and sides 

 of the neck, soiled white, or yellowish white, excepting the chin, which is 

 usually darker and like the rest of the ventral surface. The sides of the neck 

 are sometimes strongly tinged with buff. There is also a slight extension for- 

 ward on the top of the head of the general dusky color of the dorsal surface, 

 which usually forms a V-shaped area, extending to a point midway between the 

 ears and eyes. It is indistinct in outline and varies greatly in intensity and 

 extent in different individuals, being often absent, the head then being practi- 

 cally pure white. Eyes with a very narrow blackish eyering, widening 

 anteriorly into a small, usually indistinct, preocular spot, sometimes nearly as 

 large as the eye but often obsolete. Fore and hind limbs black the whole 

 length except the toes, which on the fore feet are white for half or two thirds of 

 their length, and on the hind feet for about one fourth their length. As a rule 

 there is much less white on the hind toes than on the front toes, the hind toes 

 frequently lacking the white on one foot and occasionally on both feet. The 

 nails and soles of all the feet are yellowish or flesh-color in life. Ears black, 

 broadly tipped with flesh.color (pale yellow in the dry skins), or narrowly edged 

 with this color, occasionally nearly or quite lacking. Tail clothed for about 

 two inches at the base with long hair like that of the body, the naked portion 

 brownish flesh-color, except at the base, where it is blackish ; the dark portion 

 varies in extent in different individuals, but usually occupies only the part 

 covered by the long hair. The pouch in the female is generally thickly 

 lined with crinkled woolly hair, usually rufous brown. 



Young. Nursing young (250 to 350 mm. in total length) are blackish brown, 

 finely grizzled with white hairs ; under surface scantily clothed with very short 

 blackish hairs ; whole head clear white as far as the ears, with an incipient 

 blackish eyering and anteorbital spot ; ears, wholly while ; feet and tail colored 

 as in the adult. (See Plate XXV, Figs. 3, 4.) 



Measurements. Total length in middle-aged males, 750 to 875 mm. ; head 

 and body, about 450 to 520 ; tail, about 270 to 350 ; tarsus, 60 to 70; ears, about 

 50. Females somewhat smaller. Ratio of tail length to length of head and 

 body, about 70 or less. For further detailed measurements, including measure- 

 ments of skulls, see Table I. 



Specimens examined. The material available for examination has been 

 received from the following localities : 

 [June, 7907.] 11 



