Arc/entitie, Puftiifonutti, and Cape Horn MuiitUe. 16'.) 



DimcMision.s of tlic type fmcasiircd in flesh) : — 



Head and l)ody 115 mm. ; tail 77 ; liind foot 21 ; ear 18. 



Skull: <(reatest lenj^^th 29*2; condylo-incisive lenj^th 27; 

 zygomatic Ijreadth 16 ; nasals 11*6 ; intcrorbital breadth 4'5 ; 

 breadth of brain-case 13 ; palatilar length 12*8; palatal 

 foramina 65 ; upper molar series 4"5. 



Hab. Goya, Corrientes. 600'. 



Type. Adult male. B.M. no. 98. 12. 3. 12. Original 

 number 100. Collected lOtli August, 1896, by R. Perrons. 

 Presented by Oidfiekl Thomas. Fifteen specimens examined. 



This mouse may be distinguished from the true H.venustus 

 of Cordova by its darker, less drabby colour, shorter fur, and 

 apparently rather longer ears. 



" Common. Killed in maize-field." " Trapped in quinta/^ 

 ~-R. P. 



The Jujuy species, H. musculinuf! , is smaller, paler, with 

 shorter hair, and has six or seven pairs of mammae. 



Of the smaller members of the group, the true H. laucha, 

 Desm., is an animal with head and body about 70 mm., tail 

 about 50, and hind foot 14-15 mm., as represented by the 

 Goya speeimeas. And in the south of the Argentine Water- 

 house's H. gracilipes is very closely allied to it; but I have 

 not material for a ])roper comparison. 



IJct-vveen the two, however, in the Buenos Ayres and La 

 Plata region, there occurs a mouse which I collected in some 

 numbers in 1890 and supposed to be the same as the laucha, 

 the natives even calling it by that very name. 



But comparison shows that it has a conspicuously longer 

 tail, which nearly cr quite equals the head and body in length. 

 It uiay be called 



Hesperomys muriUus, sp. n. 



General appearance very much as in Mus mvsculus. Size 

 about as in H. laucha, though old individuals may attain a 

 larger size. 



Colour mouse-grey above, slightiy more drabby poste- 

 riorly, an inconspicuous buffy wash along the sides; under 

 surface greyish white, the bases of the hairs slaty. Ears of 

 inedium size, greyish brown, a well-marked postauricular 

 M bite patcli present. Hands and feet white above; palms 

 and soles naked. Tail about as long as the head and body, 

 sometimes actually longer, but more commonly a few milli- 

 metres shorter : grey-brown above, slightly darkening 

 terminallv, whitish below. 



13* 



