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THE MAMMALS OE EGYPT. 
Mus NOEVEGicus, Ei’xleb. 
Mus noruegicus, Erxleben, Syst. Reg. Anim. 1777, p. 381. 
Mus decumanm, Pallas, Nov. Sp. Glir. 1778, p. 91, pi. xxiii.; et auct. 
Mus maniculatus, Wagu. Wiegm. Arch. 1848, i. p. 186. 
<5'. Assuan. 
This species is readily distinguished from M. rattus by its shorter and more hairy 
ears; by its shorter more thickly haired and more finely scaled tail (11 rings to 
10 mm.); larger feet, with proportionately shorter first and fifth digits; softer fur, 
shorter whiskers, and shorter and less rigid longer hairs on the back. The fifth toe 
is less expansible than in the better climber M. rattus. 
Specimen preserved in alcohol:—Head and body 180 mm.; tail 164 ; hind foot 41‘5 ; 
ear 19 ; longer hairs of back 35. 
Measurements of skull:—Greatest length 44-5 mm.; greatest breadth 21-5 ; breadth 
of brain-case 17 ; length of nasals 16; basal length 39 ; length of palate 21; incisive 
foramina 8 ; molar series 7 ; breadth outside molars 9’7. 
The skull of M. norvegicus is distinguished from that of M. rattus by its flat and 
narrow brain-case ; the parietal ridges formed for the attachment of the masseter muscles 
are almost straight; the angle formed by the meeting of these ridges and the supra¬ 
orbital ridges is found slightly in advance of the fronto-parietal suture. The molars are 
broad, the ear-conchs less rounded. The incisive foramina do not reach the plane of 
the front molars. The palate is broader. 
This subadult male from Assuan is the first example of this species from the African 
continent which has come under my notice. Eiippell described a rat from Massowah 
as M. leucosternum ; this name is very suggestive of M. norvegicus, since a patch of 
white is very frequently found on the breast of this species, and this is present in 
the Egyptian specimen. In the majority of specimens of this species a patch of hairs, 
white to the base, will be found on the chest; thus this seemingly slight and sportive 
character is of considerable systematic importance. 
This species is not so widely spread as the last and does not vary in colour to the 
same extent under special conditions; but interesting local races are in process of 
formation in the British Islands (where it has established itself only within the last 
three centuries to the almost total exclusion of the Black Rat), notably the black form 
with white chest-spot of Ireland {M. Mbernicus) and the red rat with pale butf under 
parts found in many localities in England.—W. E. be W. 
