490 Mr. 0. Thomas on 



white; sides of muzzle brown; lips, chin, chest, and inner 

 sides of limbs white. Belly whiter than " creara-bufF," that 

 of amhiyonyx being " buff " or " ochraceous buff." Hands 

 and feet coarsely grizzled grey, the digits white. Tail dull 

 brown, lightening to white terminall}', its under surface white 

 all along. In the type there is an intermediate piece of the 

 tail abruptly white all round, but this is probably an acci- 

 dental variation ; the extreme tip of the tail appears to be 

 lost, so that I cannot say what is the colour of the terminal 

 pencil. 



Skull apparently quite as in true amhiyonyx. 



Dimensions of the tj'pe (measured in the tlesh) : — 



Head and body 250 millim.; tail 315; hind foot, s. u. 51, 

 c. u. 52; ear 23. 



Skull: greatest length 64, basilar length (c.) 49; length 

 of upper molar series 15. 



Hah. Sapucay, Paraguay. 



Type. Old female. Original number 886. Collected 

 14th November, 1902, by Mr. AYilliam Foster. 



" Caught in monte. — Pregnant : one at birth." — W. F. 



Though strikingly different in colour, especially in that of 

 the underside, from the true K. amhiyonyx of Sao Paulo, 

 this fine animal is too essentially similar in other respects to 

 be regarded as more than a subspecies. Its discovery, like 

 that of Thrichomys Fosteri, adds a new genus to the known 

 fauna of Paraguay. 



Proechimys vacillator^ sp. n. 



Allied to P. Cherriei, Thos., but larger, with shorter tail, 

 shorter palatal foramina, and otiier cranial differences. 



Fur of medium length ; spines of back about 18 millim. 

 long. Rump entirely spineless. 



General colour above tawny or tawny ochraceous, more or 

 less heavily lined with the blackish tips of the spines. Sides 

 more brownish. Whole of under surface pure sharply defined 

 white. Face dull greyish brown. Outer side of limbs like 

 sides, inner white ; hands white ; feet white along their inner 

 halves (outer in the prepared skin), pale brownish along 

 their outer, hallucal, halves. Tail well haired, dark brown 

 above, dull white below. 



Skull nearly as large as that of P. cayennensis ; muzzle 

 not so elongated as in that species and the trinitatis group. 

 Nasals with their sides more or less bowed outwards, their 

 posterior end nai rowing nearly to a point, level with the hinder 

 edge of the pre-orbital bridge. Supraorbital ridges well deve- 

 loped and forming a distinct postorbital angle, but fading away 



