288 Mammals of Eastern Asia 
d. The Common Black Rat, Rattus rattus rattus, of me- 
dium size, can at once be separated by its slate-gray or blackish 
gray fur, above and below. It is medium-sized, the body and 
head 6 to 7 inches long, tail 7 to 8 inches. It is supposed to have 
lived originally in western Europe and is a black variety of 
the Roof or Alexandrine Rat of the eastern Mediterranean. 
From Europe it has been carried on ships all over the world. 
Black varieties of other kinds of Rats, which are of extremely 
rare occurrence, will not be confused with it, because they 
are likely to be smaller and to have fur of finer quality. Not one 
of the remaining species has the fur of the underparts black. 
3. Among the medium-sized gray or brownish gray Rats with 
the ventral hairs white to the roots are included the R. ander- 
soni group, the R. canus group, the R. confucianus group, two 
members of the R. rattus group (R. r. alexandrinus and R. r. 
jalorensis), and the R. berdmorei group. 
e. The Alexandrine or Roof Rat, Rattus rattus alexandri- 
nus, probably the most widely distributed of all Rats through- 
out the world, is brownish gray above, dull white beneath, and 
has the tail longer than the body. The length of the head and 
body varies from 7 to 8 inches, tail 9 to 10 inches, hind foot 1% 
to 1% inches. This is the commonest Rat around ships and 
docks. It is of great importance from the standpoint of health 
because it can carry plague and other diseases. 
f . Anderson's Rats, Rattus andersoni with its allies sappeyi, 
excelsior, and culturatus, are white-bellied forms with softer, 
usually denser pelage than alexandrinus. In Anderson's Rat the 
head and body measure 6% inches, the long tail 10 inches, the 
hind foot 1% inches. Rattus andersoni is found in Szechwan, 
sappeyi in Szechwan, excelsior in western China, and culturatus 
in Formosa. 
g. The Woolly-haired Rats, Rattus canus group, were 
originally set off as a distinct genus, Lenothrix. There are but 
