1. DIDELPHTS. 335 



jection ; their substance thick and fleshy, thickly covered, except at 

 the edges, -with dark yellow hairs ; metatragus weU developed, 

 rounded. Whole of underside a rich golden or sulphur-yellow. 

 Pouch entirely undeveloped; mammee 4-1— i=9*. Limbs very 

 short, coloured like the body, hands and feet rather browner. Feet 

 short, fifth hind toe only reaching to the middle of the first phalanx 

 of the fourth ; pads smaU. and narrow. Tail very different from 

 that of any other member of the genus, extremely thick at its base, 

 the body appearing to taper quite gradually into the tail ; its basal 

 half thickly furred like the body, then |Short-;haired, proximally 

 brown or black, terminally white ; some two inches only of the 

 under surface of the tip naked, although sometimes aU the terminal 

 half is thinly haired enough to show the scales. 



Skull very different from that of other Opossums in its general 

 outlines, owing to its very long and narrow cranial and zygomatic 

 region compared to its unusually short muzzle. Nasals short, 

 evenly expanded behind. Forehead contracted, very convex up- 

 wards. Interorbital space narrow, smoothly rounded. Postorbital 

 processes prominent, conical, the temporal ridges running inwards 

 and baokwarks from them as in 2>. opossum. Space between the 

 level of the processes and the most contracted point of the brain-case 

 usually long and narrow. Zygomata long, high and strong, but not 

 very widely expanded, the distance from the lacrymal canal to the 

 anterior edge of the glenoid fossa equal to or exceeding the distance 

 from one to the other. Palate imperfect, as in B. opossum ; posterior 

 nares very narrow, scarcely or not broader than high. 



Teeth as usual. Upper m.^ much elongated transversely, its 

 antero-posterior diameter about one third of its width. 



Dimensions. 



a.,, 2. 



a (iu spirit). g (skin). 



Adult. Adult. 



millim. millim. 



Head and body • 260 395 



Tail 212 270 



Lower leg 50 (c.) 63 



Hind foot 36 44 



Ear 13 — 



Muzzle to eye 22 (c.) 24 



SkuU, see p. 341. 



Hah. Guiana and South Brazil ; not as yet recorded between 

 these very distant localities. 



Type not in existence. 



The variation in size of this species is very remarkable, some 

 specimens, fully adult, being only half the size of others of the same 

 sex. This is well shown by the two sets of skull dimensions given 



* One specimen only. 



