42 Mr. O. Thomas on some small 



52 millim. respectively, the Cuzcaii form is evidently distinct 

 enough to deserve a name. Its skull also shows various 

 differences, among which may be specially noted the greater 

 spread of its temporal ridges. 



Marmosa rapposa, sp. n. 



Allied to M. cinerea, Temm., but with no long fur on the 

 base of the tail, with very long body-fur, and with deep yellow 

 cheeks and throat. 



Size about as in M. cinerea. Fur long, soft and fluffy, 

 the hairs of the back about 16 millim. iu length. General 

 colour above buffy grey, the crown of the head similar to the 

 back ; centre of face yellowish, passing into the grey on the 

 forehead. Orbital rings deep black, not very broad ; a spot 

 at base of whiskers also black, separated from the orbital 

 rings by a narrower yellow line. Cheeks below orbital rings 

 and lips deep orange-yellow, the hairs yellow to their bases ; 

 region between eye and ear and round the bases of the latter 

 also yellow, but the hairs greyish proximally. Ears with a 

 well-marked anterior basal projection. Chin deep unmixed 

 yellow, like the cheeks. Chest, belly, and inner sides of 

 limbs buffy yellow, darker on the chest, paler on the belly, 

 the hairs slaty basally except just along the middle line of the 

 belly. Mammary region reddish brown. Line of demarca- 

 tion on sides quite indistinct, the buffy of the back passing 

 gradually into the yellow of the belly. Outer sides of 

 limbs like back, inner sides like belly ; metacarpals brown 

 above, anterior digits and whole upper surface of hind feet 

 dull whitish. Tail practically naked from its base, the body- 

 fur not extending on to its proximal portion ; in colour, as 

 usual, it is black proximally and white terminally, the two 

 colours passing quite gradually into one another. 



Skull in size, proportions, and the development and position 

 of the postorbital processes very similar to Central-American 

 examples of M. cinerea, therefore very different to the narrow- 

 waisted skull of M. regina. Posterior part of nasals well 

 expanded. Postorbital processes triangular, but little ante- 

 rior to the broad and rounded brain-case. Middle and 

 posterior premolars approximately equal in size. 



Dimensions of the type (an old female) : — 



Head and body (in skin) 195 millim. ; tail (dried, with 

 vertebra? present) 223; hind foot s. u. (wet) 27*5; ear 

 (wet) 25. 



Skull : basal length 43*2, greatest breadth 25*3 ; nasals, 

 least breadth 3*2, greatest breadth 6*5 ; interorbital breadth 9 ; 



