from the Delta of the Parana. 97 



slender, finely scaled, brown above, whitish below, the usual 

 narrow dark line perceptible along- the lower side. 



Skull of about the same size as in 0. longicaiidatus, mar- 

 kedly larger than in O.flavescens. The interorbital region 

 broader than in the first-named, its edges sharply square, but 

 not ridged. Zygomatic plate rather less projected forward. 

 Palatal foramina ending just opposite the front edge of »«'. 



Incisors directed backwards towards the throat, tiieir angle 

 with the tooth-row about ^b°. Molars rather larger than in 

 Icngicaudatus. 



Dimensions of the type (measured in flesh) : — 



Head and body 105 mm.; tail 125; hiud foot 28; 

 ear 17. 



Skull : greatest length 27*5 ; condylo-incisive length 23"2 ; 

 zygomatic breadth l-l'l: ; nasals 1C*2 ; interorbital breadth 4; 

 breadth of brain-case 12"5 ; palatilar length 11"5 ; palatal 

 foramina C ; upper molar series 4. 



Type. Adult male. B.M. no. 17.6.1.23. Original 

 number 284(). Collected 17th February, 1^17. 



This second species of Oryzomys is an unexpected dis- 

 covery, for all over Uruguay and Argentina (apart from the 

 far south) only one species — O.flavescens or a member of that 

 group — has hitherto been known, and 0. delticola would seem 

 to be quite isolated in the present locality. 



It would appear to be most nearly allied to the Chilian 

 0. longicaitdatus, and thus bears the same geographical 

 relationship to that animal that the Parana coypu does to the 

 Chilian one. 



4, Oryzomys flavescens, Waterh. 



c? . 2825 ; and a ? in spirit. 



This, the only non-peculiar mouse in the delta, is widely 

 distributed over Uruguay and Middle Argentina. Specimens 

 vary very much in coloration, the under surface of some being 

 strongly buffy and of others white, but extremes and all inter- 

 mediate phases are found in the same localities. 



5. AJcodon arenicola hunteri, subsp. n. 



S . 2821, 2822, 2833, 2837, 2841, 2847 ; ? . 2823, 2838 ; 

 and one ? in spirit. 



Like true arenicola in colour and other characters, but 

 averaging decidedly larger, the hind foot 21-22 mm. in length, 

 while in arenicola it is ordinarily 18-1 9, rarely reaching 20 ; 



Aim. & Mag. N. Hist. Ser. 8. Vol. xx. 7 



