NOTES ON THE RATS OF THE PORT OF LIVERPOOL. 69 
20 Sewer Rats, M. norvegicus. Other names for this last 
species are “ Wharf Rat,” “‘ Barn Rat,” “‘ House Rat,” “‘ Water 
Rat,” “ Hanoverian Rat.” It is abundant everywhere in the 
British Isles. A melanic variety is found in Ireland, known as 
the Irish Rat. It is undoubtedly the original of the Domestic 
tame white Rat. I have at present a Mus norvegicus paired 
with a tame white Rat, and hope to confirm this statement. 
Mus norvegicus is readily distinguished from the Mus rattus 
group by its stouter build, shorter and thicker ears, and its 
tail which is shorter than the body. The skull is larger, and 
differs in form in the parietal and inter-parietal regions. It 
is not so good at climbing, and prefers the addition of flesh to 
its diet. | 
The general colour of Mus r. rattus is slaty—darker on the 
back, paler below ; some specimens are of a rich black. These 
were described by Millais as Mus r. ater (Zoologist, 1905). 
Mus. r. alezandrinus only differs in coloration—the upper 
parts brown and ventral slaty or light brown. 
Mus r. frugworus has the upper parts grey or brown, 
sometimes russet ; under parts pure white or pale yellow, the 
line of demarcation sharply defined along the flanks. 
In Britain, Mus r. rattus was formerly wide spread both 
on the mainland and islands. It has been carried by shipping 
from Europe to all parts of the world. 
Mus r. alecandrinus is introduced from ships. 
Mus r. frugivorus is the common rat of the Mediterranean 
region and N. Africa. It has a world-wide range. We found 
it on the Island of Socotra, where it bred true to type, there 
being no other rats in the Island. 
The appearance of Mus norvegicus in a district is generally 
followed by the disappearance of mice and the smaller species 
of rats. 
I find all the varieties clean animals to keep. My results 
in cross-breeding have not yet reached their final stage. So far 
