On Aquatic Carnivorous Coleoptera or DijtiscidcB. 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 {e.g., Nos. 90 & 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 Eretes; 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 

 Pihantus : 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 iu Noterides (Hydrocanthus Australasioe and H. funebris) in 

 Hydrovatus, Hydroporus, and in numerous species of Agabus, iu Copelatus, Ilybius, 

 Meladema, Cybister, &c. One of the most marked features of the colouration of the 

 DytiscidfB 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 bears a 

 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 {e.g., Ilybius 

 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 antennae nearly 

 always remain pale; and it is the rule in the family that the palpi and legs, as well 

 as the antennae 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 



