ALLEN : MAMMALIA : MURID/E. 73 



Mr. Waterhouse seems to have been in doubt as to whether M. xan- 

 thorhiiuis and M. cancscens were really distinct species. He says in the 

 " Voyage of the Beagle" (/. c, p. 54) : " It was with some hesitation that 

 I described this [J/. canescens\ as a distinct species in the Society's Pro- 

 ceedings. I have now re-examined the specimens, and still am unable to 

 satisfy myself whether they are varieties of Miis xanthoFliiiius or not. Both 

 of Miis canescens and of Mus xanthorJiinus, I have before me what I im- 

 agine to be an adult and a young specimen. The adult and the young 

 of M. xa)itlioyliiiiiis agree in being of a yeUoivish-brown colour, and in hav- 

 ing the muzzle and tarsi deep yellow ; both specimens of Mns canescens 

 are of a gray colour, with an indistinct yellow wash, the muzzle and tarsi 

 being tinted with yellow, as in M. xantliorJiiniisy These are just the 

 differences, as shown by the present material, that distinguish the two 

 species, as regards coloration. But there is considerable difference in 

 size, xantlioyJmuts being the larger, especially as shown by the skull, as 

 already stated, which also differs markedly in form in the two species. 



In examining the types of these species in the British Museum, in July, 

 1 90 1, I found that they had been misassigned, the two specimens of Water- 

 house's Mus canescens having been identified, respectively, as the types of 

 M. canescens and M. xanthorliinus, the Port Desire specimens being 

 designated as the type of M. canescens, and the Santa Cruz specimen 

 as the type of M. xanthorliinus, while the Hardy Peninsula specimen, 

 the real type of M. xantJiorJiinus was not designated as a type. This 

 probably explains the record made, on the authority of Mr. Thomas, in 

 Milne-Edward's report on the mammals collected by the Mission Scien- 

 tifique du Cap Horn (Mammals, p. 28), of specimens oi Akodon xantlio- 

 rhitiiis from Santa Cruz, Patagonia, which record is only intelligible on 

 the basis of the above explained misidentification of Waterhouse's type. 



Akodon canescens (Waterhouse). 



Mus canescens Waterhouse, P. Z. S., Nov. 21, 1837, '7! Z06I. Voyage 

 Beagle, Mamm., 1839, 54. Port Desire. 



Hesperoniys {Calomys) canescens Burmeister, Descrip. phys. Rep. Argen- 

 tine, TIT, 1879, 227 (ex Waterhouse). 



Hcsperomys {Ilabrothrix) xantliovhinus Thomas, in Milne-Edwards, Miss. 

 Scient. du Cap Horn, VI, Zoologie, Mamm., 1890. p. 28, pl. vi, fig. 

 I, animal. Santa Cruz de Patagonie. 



