134 DR, F. WOOD JONES ON THE [ Feb. 16, 
Pulu Selma, and some of the smaller islands to the south. d/us 
rattus has its stronghold on Pulu gangsa, where it is very 
abundant, but it also occurs on the other islands in company with 
M. decumanus. When Dr. H. O. Forbes visited the atoll in 1879, 
he noted the greatnumber of rats—these were the ‘ Robert Portner 
rats’ that had invaded the islands in the previous year, and had 
multiplied to an extraordinary extent. He makes no note of the 
black rats, and does not mention the race of ‘ original rats’ on 
Pulu tikus. 
During Darwin’s visit the only rat in the islands was this Pulu 
tikus race, and of it he says:—‘‘ These rats are considered by 
Mr. Waterhouse as identical with the English kind, but they are 
smaller and more brightly coloured” (‘ Naturalist’s Voyage,’ p.461); 
and Wallace (‘Island Life,’ p. 275) adds, ‘‘ We have here an illus- 
tration of how soon a difference of race is established under a 
constant and uniform difference of conditions.” 
In the seventy years that have passed since Mr. Waterhouse 
described the rat, the difference appears to have become more 
marked, and a description of the race is justified for the reason 
that the modern introduction of rat virus into the atoll may 
easily exterminate it. 
Haternal appearance.—The rat isa slenderly built and sleek 
looking animal]; its general colour is a warm russet-brown. The 
fur of the back is coarser, and some hairs stand out that are almost 
black, and are 30 mm. in length; these long dark hairs are more 
numerous over the hind end of the body than over the shoulders. 
The general colour of the body is a rather rich brown, the belly 
being but little lighter than the back in most specimens. The 
shorter hairs are grey at the base and bright red-brown at the 
tips; the longer hairs are dark brown to black. The fore limbs. 
are somewhat lighter than the rest of the body, but the hind 
limbs are of the general rich red-brown. The under surface is 
only slightly lighter than the back, and isa light warm brown, 
not grey; the chin and throat are somewhat lighter. The under 
surface of the scrotum of the male is covered with long bright 
red-brown hairs, brighter than those of any other part of the 
body ; the distal extremity of the scrotum is bald, the naked skin 
being a dark purplish brown. 
The vibrisse—many of them more than 60 mm. long— are 
numerous and dark-coloured. The ears are almost naked, they 
are oval and prominent and average 22 by 15 mm. The hind 
feet are large and long, their soles are dark, almost purple, 
coloured; the digits are slender, the claws are long and much 
curved. The tail very slightly exceeds the length of the head and 
body, it is darker than the body colour; it is finely scaled, 12 rows. 
to the centimetre, and sprinkled with numerous fine black hairs. 
There are two pairs of pectoral mamme, and three inguinal pairs, 
2-3=10. The tibie are almost straight, having practically no. 
‘““bow ” forwards. 
The Skull.—The skull is long and narrow, and is delicately 
