608 On new Mammals from the Loicer Amazons. 



This is only the fifth recorded specimen belonging to the 

 rare genus Mesomys. The species will probably prove to 

 range the whole length of the River Tocantins, just as 

 M. ecauddtus would appear to occur from the Huallaga to the 

 mouth of the Amazon. 



Kerodon palustris, sp. n. 



Allied to K. spixi and K. holiviensis. 



General colour above near ''wood-brown" about as in 

 pale little-annulated specimens of K. spixi, the light mark 

 on the head behind the ear practically obsolete. Under 

 surface soiled whitish, or pale Isabella, little contrasted with 

 the colour of the flanks ; very different to the white of 

 K. spixi and more as in K. boliviensis ; the hairs pale slaty 

 basally, dull creamy terminally. 



Skull in general shape most like that of K. spixi ; nasals 

 parallel-sided ; interorbital region broad and flat ; median 

 vertical ridge on supraoccipital obsolete; anterior border of 

 mesopterygoid fossa intermediate between the broad opening 

 of K. spixi and the narrow one of K. boliviensis ; in K. spixi 

 the front edge of the fossa corresponds nearly with either end 

 of Ridgway's " elliptical oval " (pi. xvi. fig. 10), while in the 

 present animal it is as in the riglit half of '' elongate ovate" 

 (tig. 5). Bulla3 smaller than in either of tlie allied species. 



Incisors completely deep yellow (''orange-bufip^^) in front, 

 the allied species having them whitish on their outer half, 

 and the yellow part paler ; their section comparatively shallow, 

 as in boliviensis, their depth, from front to back, but little 

 greater than the breadth of either of them. 



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



Head and body 225 mm.; hind foot 46; ear 25*5. 



Skull: greatest length 55; condylo-incisive length 47*7; 

 greatest breadth 30 ; nasals 21x9; interorbital breadth 11-6 ; 

 palatilar length 23-2 ; breadth of mesopterygoid fossa 4'8 ; 

 upper tooth-series (crowns) 11'7. 



Hab. Cameta, Lower Tocantins. 



Type. Adult female. B.M. no. 11. 4. 28. 31. Original 

 number 02. Collected 3rd January, 1911, bj'- Frliulein Dr. 

 E. Snethlage ; presented by the Goeldi Museum, Para. 



From K. spixi, to which on geographical grounds this cavy 

 might have been expected to be most allied, it diff'ers by its 

 slender incisors, narrower and differently shaped mesoptery- 

 goid fossa, much smaller bullae, and less white underside — in 

 some of which characters it shows affinity with K. boliviensis. 



