68 
MURIDAE RECORDED FROM VICTORIA 
Only three immature specimens of greyi are available to 
this Museum, and except in small size, they are in every way 
similar in external appearance to assimilis. Using measure- 
ments of four adult greyi published by Wood Jones, the fol- 
lowing dimensional comparison may be formulated : 
General Size. — The two species are of equal size. In assimilis females may 
attain the size of large males; in greyi they are always smaller than large 
males. 
Tail. — The tail of assimilis is long, that of greyi shorter. In large assimilis 
the tail is proportionally longer, in large greyi shorter than the mean average 
of a series. 
Pes. — In adults the pes of assimilis exceeds 31 mm. ; the pes of greyi is 
less than 29 mm. 
Skull. — Except in size the skulls of the two species are identical, as are 
also the proportional size and structure of the teeth. The same minor varia- 
tions of palatal foramina, zygomatic plate, pterygoid region, etc., occur in 
each. The skull of assimilis is larger and heavier than that of a specimen of 
greyi of the same head and body length. 
The two rats are outwardly similar. Dimensional differ- 
ences are usually considered to be subspecific rather than 
specific characters, but in this case the relative sizes of male 
and female, and the proportional length of the tail in large 
specimens, are additional constant differences, and it is better 
to regard the two as distinct species unless the gap between 
can be completely bridged. 
The rats collected at Portland are not truly intermediate, 
for though their tail and ear measurements favour assimilis 
the more important pes and skull dimensions are close to 
greyi. They further resemble greyi in the relative sizes of 
males and females, and in the proportionally shorter tails of 
large specimens. 
The following table gives dimensions of the three groups : 
Average Lengths of 
No. of 
Spec. 
Species. 
Tail. 
Expressed as % 
of head and body 
Pes. 
Ear. 
Skull. 
4 
greyi (Wood Jones) . . 
76-3 
27-2 
16 ■ 
36 • 
20 
Rats from Portland . . 
96- 1 
29- 1 
20-9 
36-2 
20 
assimilis (east. Vic.) . . 
1011 
33-3 
23-8 
40-6 
The Portland rats must therefore be grouped with greyi , 
and do not bridge the gap between that species and assimilis. 
They are therefore described as : 
