152 Mr. O. Thomas on 



breadth 12'3; nasal length 9'5 ; interorbital breadth 4; 

 palate length from henselion 10; diastema 6 ; palatal fora- 

 mina 56; length of upper molar series 3'5. 



Hab. Piura, N.W. Peru, alt. 50 m. Other specimens 

 from Catacaos. 



Tii2^e (female). Original number 496. Collected 12th April, 

 1899, by Mr. Perry O. Simons. Several specimens ex- 

 amined. 



Ihe nearest ally of this striking little mouse is Phyllotis 

 Haggardij which is half as large again and of a general grey 

 colour. 



The present is the first record of true desert-coloration in 

 South America, and even in the desert-regions of western 

 Korth Ameiica the only specimens at all approaching Phyllotis 

 gerhillus that I have seen are some of the paler examples of 

 Peromyscus Gamheli. 



Phijndomys venusius^ sp. n. 



Of about the same size as Rh. venezuelcB, with which it 

 occurs, but distinguished by its slate-mixed belly, more bushy 

 tail, darker coloration, and slightly different skull. 



Fur thick and close, not very long, the hairs of the back 

 about 8 millim. in length. General colour above rufous 

 fulvous, of a much deeper tone than in Bh. venezuelce, the 

 head and fore-quarters more fulvous, the posterior back 

 darker and more rufous. Sides with a brighter rufous edging 

 to the belly. Under surface from chin to anus slaty white, 

 the basal halves of the hairs slaty, their tips dull white, line 

 of demarcation on .sides not sharply defined. Eyes without 

 darker rings round them. Ears fairly well-haired, dark 

 brown, darker than in the allied species. Hands dull white 

 above, with a slight metacarpal darkening ; feet with these 

 colour-contrasts more strongly marked, back of heel dark 

 brown, and a decided patch of dark brown on the terminal 

 part of the metatarsus ; proximal part and sides of metatarsus 

 and uj)per surface of toes yellowish white. Tail long, well- 

 haired, pencilled at tip, the terminal hairs 12-15 millim. in 

 length, uniformly dark brown throughout. 



Skull with a narrower interorbital space than in Rk. vene- 

 zuelce. Nasals also narrowing more rapidly behind, their 

 breadth at about half their length being about 2*5 millim., as 

 compared to 3"0 or 3'2. 



Dimensions of the type (measured in skin) : — 



Head and body 121 millim. ; tail 151 ; hind foot (s. u.) 24-8. 



Skull: greatest length 33*5; basilar length 26; greatest 

 brtadlh liS'2: nasals 12x3*7; interorbital breadth 4'3 ; 



