276 Mr. 0. Thomas on Mammals from 



zygomatic breadth 21*7; nasals 9"2 ; interorbital breadth 13; 

 palatilar length 15 ; upper tooth-series 5*9. 



Hab. as above. 



Type. Adult male. B.M. no. 20. 7. 1. 8. Original 

 number S. 86. Collected 21st February, 1916. 



Tin's squirrel appears to be most closely related to M. flavi- 

 venter, Gray, of which, besides the type, the Museum possesses 

 a specimen from the Yahuas Territory, north of Loreto, 

 N.E. Peru. It differs as a species by its paler general colour, 

 its reddish ears, and its narrower and more lightly built 

 skull. 



But it also presents a puzzle as to the characters of the 

 genus Microsciurus, for with the small size and other ex- 

 ternal characteristics of the genus it has no p 3 , and might 

 therefore be thought referable to the group of Sciurus called 

 Leptosciurus by Allen. But in M. flavi venter p 3 is propor- 

 tionally much smaller than is usual in Microsciurus, and I am 

 disposed to believe that the present is a species which has 

 gone just one stage further in the same direction, unless these 

 two specimens prove hereafter to be abnormal individuals 

 without the tooth, as occasionally happens. In all other 

 respects the species is a typical Microsciurus. 



36. Sciurillus pusillus, Desm. 



? . 137 ; ? . 136. Villa Braga, Rio Tapajos (E. Sneth- 

 lage) . 



Quite like the type of Macroxus kuhli, Gray, which very 

 likely came from this region, and not from Guiana, where 

 alone Sciurillus has hitherto been supposed to be found. 



37. Holochilus sciureus, Wagn. 

 <?. 55, 111. Para. 



38. Oryzomys laticeps, Lund. 



<$ . 140. ? . 139, 141. Villa Braga, R. Tapajoz. 

 ¥ . 34. Liberdade, Rio Iriri, R. Xingu. 



39. Oryzomys subjlavus, Wagn. 

 <$ . L. 43. Ladeira Grande, Ceara (F. Lima). ■ 



40. Oryzomys navus messorius, Thos. 



S . L. 28, 29, 30 ; ? . 31. Fazenda Pacoval dos Mellos, 

 Marajo Island (.F. Lima). 



