A NEW SPECIES OF MOUSE. 
I am much indebted to Mr. H. H. Finlayson for allowing me 
to compare his Tasmanian series with the Victorian specimens ; 
except for one or two minor variations they are identical. No 
Victorian specimen is as large as the largest that he records 
(loc. cit.), but an allowance for shrinkage due to prolonged 
immersion in alcohol must be made. The tails of the Victorian 
specimens are consistently longer than those of the Tasmanian 
series, and expressed as a percentage of head and body length 
average 73% (Victoria) against 64% (Tasmania) for animals of 
the same general size. Victorian specimens, therefore, may 
be distinguished from Rattus lutreola not by their shorter, but 
by their more slender tails. The base of the tail, immediately 
beyond the body hair, of R. lutreola is 6 mm. in diameter ; 
that of Mastacomys, of similar H. and B. length, is 4 mm. On 
the whole the colour of the pelage of the Victorian series is 
brighter, the terminal band being more ochraceous, but there 
is a certain amount of variation and specimens from the two 
States grade into an unbroken colour series. 
The skulls are identical. There is a wide variation in the 
breadth of the incisor teeth, but this cannot be correlated with 
locality, nor, apparently, with age. 
The Victorian specimens are therefore recorded as Mastacomys 
fuscus Thomas, their slightly greater tail length (the only 
consistent difference) not being considered sufficient, alone, to 
warrant separation from the Tasmanian species. 
Three specimens w T ere donated by the late H. Quiney of 
Mortlake. He sent a male (Nat. Mus. No. R.1715) and a young 
female (R.1713) from Laver’s Hill in the Otway Forest, and an 
adult female (Cl 34) from his home at Mortlake, which is situated 
in the open plains 50 miles N.W, of the Otway Forest area ; 
possibly he collected this specimen also in the Otway Ranges. 
The recently trapped male was taken on the edge of a clearing 
overgrown with bracken fern at Olangolah, near Beech Forest, 
at the head of the Gellibrand River (1800 feet). The surrounding 
forest is thick, heavily scrubbed, and very wet, the average 
rainfall of the district being over 60 inches. Rattus assimilis in 
considerable numbers was caught in the same place, but 
R. lutreola is not found in the locality. Near the trap were 
many scratchings, smaller and shallower than bandicoot 
scratches, which had evidently been made in search of a Puff-ball 
(Lygoperdon) , fragments of which were lying amid the disturbed 
earth. Bandicoots are unknown in the locality, R. assimilis 
does not usually excavate for food in this way, and the scratches 
may probably be attributed to Mastacomys. It is hoped, in the 
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