98 Mr. O. Thomas on small Mammals 



and the skull 2J:-25'5 mm. in condylo-incisive length, that of 

 arenicola ordinarily 22"5-23*5, exceptional specimens just 

 surpassing 24. 



Dimensions of the type (measured in flesh) : — 



Head and body 101 mm. ; tail 81 ; hind foot 21-5 ; 

 ear 13o. 



Skull: greatest length 27*7 ; condylo-incisive length 25*5 ; 

 zygomatic breadth 13*6 ; palatilar length 12 ; palatal 

 foramina 6*7 ; upper molar series 4*5. 



Ti/pe. Old male. B.M. no. 17. 6. 1. 28. Original num- 

 ber 2841. Collected 12th February, 1^)17. 



Named in honour of Mr. James Hunter, the Managing 

 Director of tlie Isla Ella Fruit and Forest Company, to whose 

 help and kindness Mr. Kemp was so greatly indebted during 

 his visit to the Delta. 



Akodoii arenicola, the commonest mouse of the Argentine, 

 occurs in numbers in every collection that we have received 

 from the area between' Goya, Corrientes, in the north, and 

 Bonifacio, Buenos Ayres, in the south, in Southern Uruguay, 

 and Eastern Buenos Ayres, and it is everywhere of very 

 uniform size and coloration. Only here, almost in the centre 

 of its general range, but undei: exceptional local conditions, 

 there is so considerable an increase in its size as to deserve 

 recognition by name. 



" From the osiers " ; " from an overgrown orchard " ; 

 " from the virgin jungle-growth " ; " from withy beds.'^ — 

 E.K. 



6. Deltamys kempi, gen. et sp. n. 

 (J . 2836, 2840, 2848 ; ? . 2830. 



Deltamts, gen. nov. 



External characters as in Akodon, claws and fur normal. 

 Eyes small. Skull remarkabl}' narrow, both as regards the 

 breadth of the cranium and the lateral spread of the zygomata ; 

 zygomatic breadth less than half the condylo-incisive length. 

 Supraorbital edges rounded or with a mere trace of the 

 normal squaring. Zygomatic plate scarcely projected for- 

 wards. First upper molar with anterior notch. Second 

 upper molar with the small antero-external cross-ridge 

 obsolete. 



Genotype: Deltamys kempij sp. n. 



This genus is clearly one of the Akodont series, of which 



