Journal of the Federated Malay States museums - Sabrizain.org

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II. A NOTE ON THE VARIATION OF A LOCAL
I
RACE OF EPIMYS RATI - i RATTl S
JARAN (BONHOTE), i ROM PULAU JARAK,
STRAITS Of M vL.U CA.
By H. C. Robinson, C.M.Z.S.
I
In an earlier number ol vol. i, pp. 70, 71
119051. Mr. j. L. Bonhote
specimen obtained by me ii
described this rat
1904.
on a single
The mth 1 1
,:. rded it as a rao t the Sumatran
rttink), but the acquisition ol lar.ye series of
closely allied foi ud and from various
groups of islands show that it is rather to be regarded as
a form of the cosmopolitan E. rattus.
(
In view of the fact that Pulau Jarak is very isolated and
is practically never landed on, 1: 31 mm h as it possesses no
beach and is steep to right up to the masses of granite
boulders that form the shore, it is probable that the local rat
population is hardly, it ever, contaminated by the introduction,
whether by man or by natural agencies, of fresh blood. The
race has therefore, in bility, had time to attain
a position of more murium and I have
therefore compiled the follow ins; tables based on a very considerable
series obtained during two 01 three days in April, 1915.
The specimens wi by two natives and were
ought it advisable to
measured by them, but 1
submit their* figures to analysis as the personal error is
probably large nstant a race almost
certainly masks the individual variation. It is, moreover,
difficult to tell from skins whether tne tails are really perfect,
while the fo it-measure, even for experienced European
collectors, is subject to a. personal or individual error, which is
relatively considerable.
The measurements on the skulls have all been taken by
myself with fine pointed dividers on a metal scale, the tenths
of millimetres being estimated and in this connection it is well
to consider the errors inherent to the methods of measurement,
as ring on modern work
in mammalol gy, lo al rai ften founded on small
differences in measurements based on series which from a
biometrical point of view are frequently small.
Masking errors may therefore be introduced from the
following cases :
(1) A skull which has been comparatively recently
cleaned, has been overboiled in the
process of cleaning, will always give slightly
larger measun to opening of the
sutures; in the case of badly overboiled skulls
this increase is permanent.
August, 1916. 2