228 
HORN EXPEDITION—CRUSTACEA. 
(lays aftei’wards when the water had subsided and that which remained in the 
deeper holes liad liecome clear there was not a trace of living ones to be seen. 
The rate of growth of the Apus and Estheriadie must be very great. Certainly 
not more than two weeks after the fall of rain and probably only a few days 
numberless specimens of Apus measuring in all about 2^-3 inches in length were 
swimming about and as not a single one was to be found in the water-pools prior 
to the rain these must have been developed from the egg. The same is true of 
the large Limnadopsis. It is difficult to understand why on the one hand Estheria 
packardi should persist as long as there remain suitable water-holes, and why on 
the other hand from the same water-holes its close allies, Limnadopsis squirei and 
Z. tatei, should so completely disappear. 
At Conlon’s Lagoon, for example, not far from Alice Springs, one special part 
of the low land close to the lagoon was studded with the dried-up carapaces of 
Z. squirei but not a single one was to be found in the muddy water of the lagoon 
close by though in this E. packardi was swimming about. 
Estheria packardi, with its three well-marked varieties, may certainly both in 
numbers and persistency be regarded as the dominant .species. One form, E. 
dictyon, is evidently very local. We only found it once in a dried-up condition in 
the bed of the Palm Creek and a few spirit specimens (locality uncertain) 
containing the soft parts were included in the collection of the South Australian 
Museum. 
It is worth noting that every species yielded specimens of both males and 
females. In the Estheriadte the numbers may, roughly speaking, be said to be 
about equal and amongst fifty-eight specimens of Apus six are males. There is 
no difference in size between the sexes. 
All the Estheriadie swim with the dorsal surface uppermost and the valves of 
the carapace open widely enough to admit of free movement of the appendages. 
Apus, on the contrary, as is well known swims with the ventral surface upper¬ 
most. Possibly this difference in habit may be attributable in part to the fact that 
in the former the valves can be rapidly closed so as to cover the softer and more 
vulnerable parts, whilst such closure is impossible in Apus. 
Whilst watching Apus swimming about, one was seen to come suddenly to 
the surface struggling violently and on being caught was found to have three 
water-beetles tearing its soft appendages. These beetles are always darting up and 
down in search of food and if the Apus swam with its ventral surface downwards 
it would probably more often fall a prey to such voracious enemies. 
