100 On small Mammals from the Delta of the Parana. 
specially narrowed behind. Mesopterygoid fossa broad, twice 
as wide at its anterior end as the base of the narrow ptery- 
goids on each side of it; in most members of the Akodont 
group the base of each pterygoid is as broad as the fossa 
between the two. Bulle small, as in Akodon. 
Incisors rather thrown forward, their angle with the molar 
surface 80°-83°. Molars light and slender, their structure 
as already referred to. 
Dimensions of the type (measured in flesh) :— 
Head and body 89 mm. ; tail 85 ;. hind foot 22; ear 13. 
Skull: greatest length 25°6; condylo-incisive length 24 ; 
zygomatic breadth 11°7; nasals 92; interorbital breadth 4°4 ; 
breadth of brain-case 10°8 ; palatal foramina 5:7 ; breadth of 
mesopterygoid opening 1°5 ; upper molar series 4. 
Type. Adult male. B.M. no. 17.6.1. 35. Original 
number 2830. Collected lst February, 1917. 
This little blackish mouse is a most interesting addition to 
the fauna of Hastern Argentina, being so very different from 
any other animal known there. Like Oxymycterus tomen- 
tosus, similarly dark-coloured, it is no doubt peculiar to the 
marshy and water-logged region of the Parana delta, and has 
on this account escaped discovery until Mr. Kemp’s visit to 
the islands. 
“From neglected orchard” ; “from the jungle pajanal.” 
—R. K. 
7. Oxymycterus platensis, Thos. 
3. 2827, 2844; 2. 2820. 
8. Myocastor coypus bonariensis, Geoff. 
Two skulls. 
9. Cavia pamparum, Thos. 
Four skulls. 
10. Blastocerus diehotomus, Il. 
9. 2850. 
“ Presented by Mr. F. E. Welch.—Snared by a quintero.” 
—Rh. K. 
11. Lutreolina crassteaudata, Desm. 
o. 2811, 2816. 
