HORN EXPEDITION—MAMMALIA. 
41 
The two specimens (both males) collected by us are somewhat darker in 
colour than the one figured by Mr, Alston.* 
In addition to the characters usually given it may be noted that along the 
anterior edge of the ears runs a strongly-marked fringe of long white hairs, 5 mm. 
in length. 
In his work on “ Marsupials and Monotremes,”t Mr. Lydekker says, referring 
to a remark made by Mr. Thomas dealing with the method of progression of 
Antechinomys, “this saltatory mode of progression having been doubtless developed 
in accordance with the exigencies of the arid sandy country inhabited alike by 
Antechinomys and Hapalotis.” 
Watching the animals in their natural surroundings, it is really somewhat 
difficult to see what is exactly the advantage gained by such small forms of animals 
in this saltatory mode of progression. The country in which they usually live is 
covered with big tussocks of grass and shrubs of various sizes. With a larger 
animal, such as a kangaroo, it is doubtless an advantage to be able to go straight 
ahead instead of having to “ dodge round ” tussocks of grass; but neither the 
Hapalotis nor the Antechinomys gain any such advantage, as both are far too 
small to spring over the grass tussocks, and perhaps the most noticeable point in 
connection with this matter is that the true mouse, which lives in great numbers 
in the same part and has not taken on this saltatory method, thrives just as well. 
What the small animals, whose chief enemies are birds of prey, appear to need 
is the power of I’apidly gaining the shelter of a shrub or tussock of grass, and there 
lie so close to one another, that a running animal such as a true mouse can do this 
as rapidly as a jumping animal such as a Hapalotis can, possibly even a little more 
rapidly, as the run into shelter is a continuous one, whereas, when the Hapalotis 
or Antechinomys has taken a jump bringing it close to shelter, there must be a 
slight pause prior to the final run. A very slight difference in time when a hawk 
is in pursuit will save or lose the animal its life. Possibly the real advantage in 
the saltatory method of progression amongst these small forms lies in the greater 
difficulty of pouncing down upon an animal travelling by leaps and bounds rather 
than in any advantage gained in the way of speed. So far as travelling over the 
ground is concerned, a mouse can and does do it just as well as a Hapalotis. 
It is somewhat curious to notice that two animals so differently organised as 
Hapalotis and Antechinomys have taken on the same habit and live side by side, 
one in large numbers and the other very scarce. 
* P.Z.S , 18S0. 
t Allen’s Naturalist’s Library, “ Marsupials and Monotreines,” p. 181. 
