794 MR. J. LEWIS BONUOTE ON A SMALL [NoV. 0, 



Two forms of this species occur : — 



a. Mus rattus tectoriim, 



in which the fur of the uurlerparts is white to its base. 

 Average hind-foot measurement 35 mm. 



b. Mios rattus alexandrimi-s, 



in which the fur of the underparts is wholly or paiiially 



slate-coloured. Average hind-foot measurement 33 mm. 



I made a considerable study of the variations of this species, 



the results of which I am now working out and hope to publish 



in a separate paper. 



Mus NORVEGICUS Erxl. 



Mus norvegicus Erxl. Syst. Reg. Anim. p. 381 (1777) ; de Wint. 

 in Anders. Zool. Egypt, Mamm. p. 276 (1902). 



This rat is now becoming very common in some districts though 

 at present its distribution seems rather erratic. It is said not to 

 occur in Cairo itself, though on the other (w"estern) side of the 

 Nile it is very numerous. Oapt. Flower tells me that it has been 

 found in the Zoological Gardens only within the last eight years, 

 and in that time it has completely ousted Arvicanthis which used 

 formerly to abound there, and qviite Hfty per cent, of the " rats " 

 caught in the Gardens now belong to this species. I procured 

 two specimens in the Fayum. 



Mus MuscuLus Linn. 



Mus gentilis Brants, Muizen, p. 126 (1827). 



Mus orientcdis Cretzschmai% Riipp. Atlas, p. 76, pi. 30 (1828). 



Mus musculus Linn. Syst. Nat. x. p. 62 (1758) ; de Wint. 

 in Anders. Zool. Egypt, Mamm. p. 277 (1902). 



Two forms of this species are apparently found in the Giza 

 Gardens. One form may, I think, be known as Mus in. gentilis 

 (Brants), in which the hairs of the under parts are white to their 

 bases and the whole animal is of a more fulvous tint. 



The other is Mus m. orientcdis Oretzschm. In this form the 

 hairs of -the under parts have slate-coloured bases. The general 

 colour is greyer than in Mits m. gentilis, and a clear line of fawn 

 along each side separates the coloui- of the upper fiom that of the 

 under parts. 



Arvicanthis niloticus (Desm.). 



Arvicola niloticus Desmarest, Eucy. Method., Mamm. Suppl. 

 p. 281 (1822). 



Arvicanthis niloticus (Desm.) de Wint. in Anders. Zool. Egypt, 

 Mamm. p. 279 (1902). 



This species is extremely common throughout the country. 

 It lives almost entii-ely in the open fields except during the 



