98 Mr. O. Thomas on small Mammals 
and the skull 24-25°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 13°5. 
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. 
Type. Old male. B.M. no. 17. 6.1. 28. Original num- 
ber 2841. Collected 12th February, 1917. 
Named in honour of Mr. James Hunter, the Managing 
Director of the Isla Ella Fruit and Forest Company, to whose 
help and kindness Mr. Kemp was so greatly indebted during 
his visit to the Delta. 
Akodon arenicola, the commonest mouseof 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, iu the south, in Southern Uruguay, 
and Hastern Buenos Ayres, and it is everywhere of very 
uniform size and coloration. Only here, almost in the centre 
of its general range, but under 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.’”’— 
pk. 
6. Deltamys kempi, gen. et sp. n. 
3. 2886, 2840, 2845 ; 2. 2830. 
DELTAMYS, gen. nov. 
External characters as in Akodon, claws and fur normal. 
Eyes small. Skull remarkably 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 kempi, sp. n. . 
This genus is clearly one of the Akodont series, of which 
