On Aquatic Carnivorous Coleoptera or Dytiscide. 541 
narrow band near the outer margin not reaching quite to the shoulder or apex, and 
just within this, beyond the middle, one small spot, or two small spots close together ; 
sometimes there isa small basal spot on each side the scutellum and these may be 
extended so as to form a transverse yellow basal band ; my individuals of this form 
are chiefly from Melbourne and Adelaide, but I have it also from more northern 
parts, and even from the extreme North-west of Australia individuals are before 
me scarcely differing from the Melbourne individuals. The second form is rather 
larger, about 72-8 m.m. long, and differs from the preceding chiefly by the greater 
extension of the yellow marks of the upper surface, these asume the form of six or 
eight rather regular lines on each elytron, and a transverse band across the middle 
of the thorax ; and in this form the hind legs are rather thicker and shorter than in 
the first form ; the markings of the upper surface are however so variable that it 
is difficult to find two individuals in which they are quite similar, the band across 
the middle of the thorax becomes more or less effaced, and the longitudinal lines on 
the elytra become interrupted, and at the points where they are interrupted coalesce 
more or less, so as to form irregular spots, and the spots formed at these points of 
coalescence sometimes remain when all other traces of the longitudinal lines on the 
wing-case have disappeared; the specimens I have seen of this form, are from 
Paroo river, Swan river, Darling river, Sidney, and West Australia. 
The third form is again similar to the first one but is shorter and flatter, about 
63-7 m.m. long, and has the hind legs shorter and thicker than in the first form, 
and it also has the thorax more strongly transverse, the anterior yellow spot on 
the head is conspicuous as is also that on the anterior angle of the thorax, but the 
yellow marks on the elytra are even less conspicuous than in the first form, the 
lateral line being more abbreviated anteriorly, and the one spot beyond the middle 
near this line smaller ; this form seems specially common on the North-eastern parts ; 
I have it from Sidney, Port Denison, Port Bowen, Brisbane, Rockhampton and 
Gayndab, and it is probably this form that Macleay named Agabus mastersi. 
The fourth form is in its well marked developments very different, it is large, 
about 8 m.m. long, and instead of having the upper surface very shinning, it is dull 
and greasy or silky looking, and the reticulation of the elytra is very indistinct, 
the middle yellow spot on the head is not large, and the yellow marks on the elytra 
are extremely reduced so as to appear quite absent, but on examination more or 
less evident traces of the sublateral band and its adjacent spot (as mentioned in form 
No. 1) can always be found; the hind legs are long and slender, and the lateral 
wing of the metasternum is a little larger than in the other forms. This variety 
has been found at Clyde river, and also by d’Albertisi in the mountains of Victoria 
in October, 1874. 
The majority of the individuals I have observed from Australia may be referred 
to the above four forms, but there are various points of structure, besides those already 
alluded to, which are variable; among these may be mentioned the width of the 
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