On Aquatic Carnworous Coleoptera or Dytiscide. 193 
frequently run into one another laterally, so as not to be readily distinguished. Many 
‘species of Deronectes are also variegate with black and yellow, but the colouration 
is less distinctly of a linear character than it is in the insects just referred to. The 
Laccophilini vary much in colour, and are usually pallid ; frequently they are marbled 
with darker tints in a very indefinite manner, but some species (¢.g., Nos. 96 & 97) 
become definitely and prettily marked: a very curious colouration is found in several 
‘species of Laccophilus (No. 156 and allied species) consisting of numerous 
very waved longitudinal dark lines, such as I have not seen in any other beetles. 
‘The most pallid species of the family are the two EHretes; E. australis is of an entirely 
pale colour, except that the wing-cases are covered with numerous rather large 
punctures, each of which is black; the second species of the genus (Dytiscus sticticus 
L.) has the same peculiarity, but has in addition a black fascia on the wing-cases, 
and frequently also another on the prothorax. The colouration of the wing-cases 
in Acilius resembles that in Eretes, except that the punctures are not so large and 
definite and the black colour is not limited to a single puncture, but connects two, 
three or more punctures together, giving rise to an irregularly speckled appearance 
approximating to that which I have already described as existing in the genus 
Rhantus : the irregular black fascia on the wings of Dytiscus sticticus just alluded 
to is produced in a similar manner. An entirely black surface is quite frequent in 
the family, and is found in Noterides (Hydrocanthus Australasize and H. funebris) in 
Hydrovatus, Hydroporus, and in numerous species of Agabus, in Copelatus, Ilybius, 
Meladema, Cybister, &c. One of the most marked features of the colouration of the 
Dytiscidee is the fact that the lateral margins of the thorax and wing-cases are very 
frequently of paler colour than the rest of the upper surface, so that the body bearsa 
more or less definite band of pale colour defining the outline of the upper surface; this 
yellow band finds its greatest development in the genera Dytiscus and Cybister, 
where it very frequently forms a perfectly definite lateral stripe of yellow colour ; 
in other genera, however, the stripe is not so distinct and definite (¢.g., Iybius 
fenestratus) and even in Cybister there are some species where the lateral margin 
is only indefinitely paler. In Ilybius and numerous species of Agabi which have a 
very dark coloured upper surface, a minute dot or dash of pale colour (or both of 
these) exists on the wing-cases, near the apex and lateral margin. 
In the Hydaticides the head and thorax bear with great frequency transverse 
marks of pale and dark colour on the head and prothorax and in numerous species 
of Dytiscus the whole of the prothorax is definitely margined with yellow ; and this 
is found again in two species of Cybister (Nos. 1,154 and 1,155). 
Although the colour of the body is so frequently black, the antenne nearly 
always remain pale; and it is the rule in the family that the palpi and legs, as well 
as the antenne are paler than the rest of the body ; the swimming’ legs however 
are very frequently darker in colour than the other legs. 
Another peculiarity of frequent occurrence in the family, is the existence of two 
