198 THE ZOOLOGIST. 



noticed. The aboriginal hunter puts a dead fish in the water 

 outside the hole of the " Djinnjokma," and waits with a light 

 spear all day for the animal to come out and feed ; but very often 

 he waits in vain, at least, that is my experience. 



Only once on the Daly, in the month of August, an aborigine 

 brought me a living adult female specimen with three young 

 ones, and a few juvenile specimens were received later. The 

 Hydromys is strong, of a very savage temper, bites hard, and 

 when irritated gives vent to a grunting squeak. 



Muridce. 



The common Black Rat, Mas rattus, was observed in Arn- 

 hem Land, and frequently found in the dwellings of colonists. 

 Except in these houses and their immediate surroundings, I did 

 not observe it ; but I am unwilling to lay any stress on the cir- 

 cumstance that no specimens of this species came to my notice 

 during my travels in the forests. It may easily have escaped my 

 attention, and the animal may, but certainly not to any great 

 extent, inhabit the woods of the north. The species is undoubt- 

 edly introduced either by European ships or Malay trepang- 

 fishers, the latter for centuries having every year visited the 

 northern coasts of Australia. 



Arnhem Land was inhabited not only by Mus rattus, but by 

 a number of small species of the genus Mus, the specific deter- 

 mination of which has proved impossible, chiefly owing to the 

 small series of specimens collected. These forms are undoubt- 

 edly indigenous to the country, and belong to the original fauna 

 of Australia. They are so numerous and so widely distributed, 

 even to the remotest parts of Arnhem Land, that they can scarcely 

 be considered as introduced. In places where the white man had 

 seldom, if ever before, trod, they seemed to occur in the greatest 

 numbers. 



These mice and rats, the size of which generally averages 

 about that of the common Cricetus frumentarius of Europe, play a 

 quite important part in the economy of nature. In order that 

 the soil, even in its pristine condition, shall retain its power of 

 nourishing vegetable life, a constant turning and renewal is neces- 

 sary. Subsoil must in one way or another be conveyed to the 

 surface, and replace that which has become deficient in nourishing 



