South. American Rodents. 447 



Skull lightly built. Back ot" nasals and front part of 

 frontals markedly concave upwards along the middle line. 

 Supraorbital edges sharp, not heavily ridged. Palatal 

 foramina well open. Molars decidedly narrower than in 

 other species. Last upj)er molar rather siin|)lcr than in other 

 species, its anterior lamina directly transverse, scarcely 

 thickened internally, not connected with the second lamina. 



Dimensions of the type (measured in flesh) : — 



Head and body 175 tnm. ; tail 164 ; hind foot 38; ear 17. 



Skull : greatest length 36'7 ; basilar length 30 ; greatest 

 breadth 19*5; nasals 14; interorbital breadth 4*5 ; ])alatilar 

 length 18 ; diastema lO'G ; palatal foramina 7'5 X 2'5; upper 

 molar series 6"9 ; breadth of ni" 'll. 



Ilab. Chaeo 1 league N.W. of Concepcion, Paraguay. 



Type. Female. B.M. no. 1. 3. 11. 2. Collected 12th 

 March, 1900, by Mr. T. Insley. One specimen. 



" Inhabits swamps. — Raises a nest on weeds about a foot 

 above the water.'' — T. I. 



This species is distinguishable from //. vuJpinus of the 

 lower Parana and La Plata, which it resembles in colour, by 

 its delicate feet and narrow molars. When further examples, 

 of different ages, of both forms are available for examination, 

 I also think it probable that a real difference in the structure 

 of m" will be definable. 



Holochilus halnearum, sp. n. 



A small species, with short tail and large teeth. 



Fur long and fine, the hairs of the back 14-15 ram. in 

 length. General colour of the usual type, the back rather 

 greyer than in //. chacarius, the sides rather duller buff and 

 the belly a deeper buff, so that there is less difference between 

 the sides and belly, the hairs of the last-named part broadly 

 slaty at base ; pectoral and inguinal light patches more 

 strongly contrasted white. Feet comparatively short ; soles 

 naked, granulated, with more strongly marked pads than in 

 the allied species. Tail comparatively short, blackish above, 

 dull greyish below. 



Skull short and thickly built. LUerorbital region but 

 slightly concave mesially. Palatal foramina broad, but not 

 widely open, owing to their rounded margins and the breadth 

 of the septum, so that the actual slits are unusually narrow. 

 Molars unusually broad and heavy, their length scarcely more 

 than in //. chacarius, but their breadth considerably greater. 

 Anterior lamina of m^ thickened internally and connected with 

 the next lamina by an enamel band. In their position also 



33* 



