CEcomys and Marmosa//om Amazonia. 379 



three equally large members of (Ecomys by its much richer 

 colour, in marked contrast to its white belly. 



In 1906* I formed the subgenus CEcomys for a number of 

 rats which combined something of the external appearance of 

 Rhipidomys with the characteristic palate of Oryzomys ; but, 

 as I failed to find any cranial distinction from the latter 

 genus, I only considered it as a subgenus. Now, however, I 

 find that, as is still more marked in Rhipidomys, the outer 

 plate of the anterior zygoma-root is hardly projected forward 

 in front of the upper bridge, while in Oryzomys there is 

 always a strongly marked projection. As the group is 

 undeniably a natural one, easily recognizable externally, I 

 think this character, slight though it is, will justify our 

 treating (Ecomys as a full genus. A list of the known species 

 is published in the paper above referred to. 



Marmosa emilice, sp. n. 



Smallest of the known species ; tail excessively long. 



Most nearly allied to Al. pusilla, Desm., but even smaller 

 (combined length of three anterior molariform teeth 4"2 mm. 

 instead of 4'4). Fur soft and fine; hairs of back about 6-5 mm. 

 in length. General colour above dull fawn, the extreme tips 

 of the hairs washed with dark brown. Under surface buffy 

 white (rather paler than Ridgway's cream-buff), the hairs 

 pale to their roots, ^\irhout slaty bases. Black eye-rings 

 well-marked. Ears rather larger than in M. pusilla. Hands 

 and feet dull whitish above. Tail nearly twice the length of 

 the head and body, its extreme base only hairy, the remainder 

 practically naked, uniformly dark brown above and below. 



Skull much as in M. pusilla. Teeth as in that animal, 

 except that the secator, instead of being fully as large as or 

 larger than the tooth next in front of it, is distinctly smallei-, 

 its vertical height from the cingulum being about 0*7 ram. 

 as against 0'9 mm. in the anterior tooth. 



Dimensions of the type (measured in the flesh) : — 



Head and body 75 mm. ; tail 142 ; hind foot 13 ; ear 16. 



Skull: greatest length 23-5; basal length 21; zygo- 

 matic breadth 13; interorbital breadth 4*2; palatal length 

 12*2 ; combined length of three anterior molariform teeth 4"2. 



Hab. Para. 



Type. Subadult male. B.M. no. 9. 3. 9. 10. Original 

 number 30. Collected loth February, 1909, by Frauleiu 



. * Ann. & Mag. Nat. Hist. (7) xviii. p. 441. 



