Argentine^ Patagonian, and Cape Horn Muridae. 183 



Dimensions of the type (measured in flesh) : — 



Head and body 115 mm, ; tail 77 ; hind foot 21 ; ear 18. 



Skull: greatest length 29'2; condylo-incisive length 27; 

 zygomatic breadth 16 ; nasals 11*6 ; interorbital breadth 4*5 ; 

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

 foramina 6'5 ; upper molar series 4'5. 



Hab. Goya, Corrientes. 600'. 



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

 number 106. Collected 10th August, 1896, by R. Perrens. 

 Presented by Oldfield Thomas. Fifteen specimens examined. 

 This mouse may be distinguished from the true H. venustus 

 of Cordova by its darker, less di'abby colour, shorter fur, and 

 apparently rather longer ears. 



" Common. Killed in maize-field.'' " Trapped in quinta.''* 

 ~R. P. 



The Jujuy species, H. musculinus, is smaller, paler, with 

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



Of the smaller members of the group, the true ff. 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 specimens. 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 proper comparison. 



Between the two, however, in the Buenos Ayres and La 

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

 numbers in 1896 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 or quite equals the head and body in length. 

 It may be called 



Hesperomys murillus, sp. n. 



General appearance very much as in Mus nmsculus. Size 

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

 larger size. 



Colour mouse-grey above, slightly more drabl)y poste- 

 riorly, an inconspicuous buffy wash along the sides; under 

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

 medium size, greyish brown, a well-marked postauricular 

 white patch 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 iew milli- 

 metres shorter : grey-brown above, .slightly darkening- 

 terminally, whitish below. 



13* 



