"208 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



sutures are obliterated, so that its extent can only be determined by the two large 

 punctures which mark the anterior limits of the lateral gular sutures. 



The eyes in the Dytiscidee are always very large, and are placed at the sides of 

 the head, but also encroach largely on its upper and under surfaces ; they are verv 

 smooth and very finely facetted, but in this latter respect there exist some slight 

 differences, as may be seen by a comparison of Agabus and Hydrovatus, with Eretes 

 and Laccophilus, the facets being distinctly larger in the former genera. When 

 looked at from the front of the head the curved outline of the eye is frequently 

 much indented or emarginate just behind the antenna, by the side of the front 

 part of the epicranium ; but in other cases the outline is preserved nearly intact at 

 this point, so that the eye may be described os possessing in front a circular inner 

 margin : Agabus and Hydrovatus may be referred to as exhibiting the former, 

 Eretes and Cybister as exhibiting the latter structure ; as might be expected inter- 

 mediate forms occur as regards this point, such are seen in Laccophilus, and even 

 in Dytiscus. 



The labrum is usually quite conspicuous, and placed on the front of the 

 epistome or clypeus in such a manner as to continue its curve ; but in a few 

 p-enera it is more or less withdrawn to-the under surface of the head, and is corres- 



O 



pondingly inconspicuous ; in Queda it is comjaletely concealed, and in Pachydrus, 

 and numerous species of Hydrovatus its front margin alone can be seen ; in 

 Hyphydrus although visible and exserted, it is placed more on the under surface of 

 the head ; this position of the labrum depends entirely on the formation of the 

 front of the epistome, for the labrum being always attached to the front edge of 

 this part, varies in position according as this is inflexed or not ; thus in Queda and 

 Pachydrus the front of the epistome is quite doubled or folded under, and thus 

 carries the labrum back to the under surface of the head, while in Hyphydrus the 

 front of the epistome, though not completely doubled under, is placed at right angles 

 to its posterior part, and the labrum assumes a corresponding position ; Coelambus 

 is a variable genus as regards the form of the front of the clypeus, and the ex- 

 posure of the labrum. In its form the labrum shows but little variation; it is 

 always strongly transverse, greatly broader than long, and its front edge is more 

 or less emarginate in the middle, the emargination varying much as regards its 

 breadth and depth ; the curve of the emargination is fringed with cilite implanted in a 

 transverse groove: in Queda where the labrum is concealed, the whole of its anterior 

 edge appears to be set with elongate fine cilioe, and in Hyphydrus the cilire extend 

 nearly across the w^hole breath of the labrum, but in the great majority of the 

 family the rule is that the emargination of the labrum is confined to a comparatively 

 small width in the middle, and the cilife are quite short. In the Noterides the 

 emargination is very slight, and the cilise are quite wanting : in Dytiscus latissimus 

 the emargination is very slight. The labrum is always yellow in colour, and its 

 upper surface is completely destitute of the isolated exserted setse which are so con- 



