Mammals from South America. 571 



Skull slender ; upper profile strongly bowed at fronto - 

 nasil suture, concave in interorbital region, convex again on 

 brain-case. Nasals unusually broad anteriorly, and not 

 strikingly narrowed behind. Supraorbital ridges fairly well 

 developed, but not rising vertically, continued back to the 

 outer corners of the interparietal. Outer plate of zygomatic 

 root but little projected forwards in front of the upper bridge. 

 Palatal foramina rather short, widely open. Lateral pits and 

 foramina on each side of the posterior palate but little 

 developed. Bullae small. 



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



Head and body 203 mm. ; tail 251 ; hind foot 32 ; 

 ear 18. 



Skull: greatest length 43; condylo-incisive length 39; 

 greatest breadth 21'5 ; nasals lb' x 5*6 ; interorbital breadth 

 7*7 ; breadth between ridges on parietals 13*7 ; zygomatic 

 plate 4'6 ; palatilar length 19; diastema 12; palatal fora- 

 mina (3'7 X 4 ; upper molar series fr$. 



Bab. Mindo, N.W. of Quito, Ecuador. Alt. 4213 ft. 



Type. Adult female. B.M. no. 13. 10. 24. 58. Original 

 number 168. Collected 4th July, 1913, by Gilbert 

 Hammond. Presented by Oldfield Thomas. Two speci- 

 mens obtained. 



The genus Nectomys falls into two groups, firstly, the 

 common widely spread and dominant species related to 

 JV. squamipes (N. apicalis, garleppi, fulvinus, &c, &c), all 

 of which are approximately of the same size and general 

 character of coloration, and, secondly, a few isolated species 

 differing widely in size and general characters, but none the 

 less showing their relationship to the ordinary JS T ectomys 

 by their glossy fur and heavily ridged skulls. Of these 

 N. russulus is the nearest in size to N. hammondi, but is 

 still a good deal smaller, while N. esmeraldarum and 

 A 7 , dimidiatus are again conspicuously smaller. On the 

 other hand, N. saturatus, from Ibarra, Ecuador, is altogether 

 a larger and heavier animal. 



It is probable that such species as the present are rather 

 less aquatic in their habits than the members of the 

 squamipes group. 



Oryzomys arenalis, sp. n. 



A very small pale form of the " Oligoryzomys " group. 



Size less than in any of the allied species. General colour 

 above near " clay-colour," the underlying colour buffy, lined 

 with dark brown. Head slightly greyer and less buffy. 

 Sides buffy, a more or less distinct buffy line edging the 

 belly. Under surface creamy white, with a slight shade of 



40* 



