On Aquatic Carnivorous Coleoptera or Di/tiscidcB. 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 is a small basal spot on each side the scutelluin 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 difteringfrom the Melbourne individuals. The second form is rather 

 larger, about 7^-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 

 6i-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, Piockhampton and 

 Gayndah, 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 sill<y looking, and the reticulation of the elytra i-< 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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