On Aquatic Carnivorous Coleoptera or Dytiscidce. 205 



large size in Meladema. In the Agahini and some of the neighbouring genera, the 

 clypeal depressions appear to be entirely wanting, but on a careful examination of 

 Dytiscus bipustulatus it will be seen that the front of the clypeus appears to be 

 provided with a fine margin, and on looking at other species of the genus (Agabus) 

 it will be seen that the depression causing the margin arises from the extension in 

 the transverse direction of the clypeal depressions. 



The clypeus or epistoma is usually of a paler colour than the part of the head 

 behind it, this is displayed in a very marked manner by the species of the genus 

 Dytiscus, where the clypeus is yellow, and the front of the epicranium nearly black ; 

 the darker colour of the epicranium frequently extends more or less on to the 

 clypeus, so as to leave the anterior portion of this latter paler than the posterior 

 part, but it is onl}' very rarely indeed that the anterior portion of the clypeus is 

 quite black in colour. 



The upper surface of the head shows no trace of any other suture besides the one 

 existing between the epicranium and clypeus ; the transverse suture between the 

 epicranium and protocranium which is very strongly marked in most of the Carabidae 

 (in the natural condition concealed by the pronotum) being completely absent. 

 The front of the epicranium on each side bears a well-marked irregular depression 

 or fovea, which is occasionally more or less distinctly divided into two depressions 

 placed one before the other (Meladema) ; these frontal fovese are entirely absent 

 in the Noterides, and are only very indefinitely present in Hyphydrus, and some 

 other Hydroporides, and are very much effaced in many members of the familv 

 having a very smooth and polished surface, such as the Hydaticides and Laccophilini ; 

 these fovese are more punctate than the rest of the upper surface, and carry some 

 very fine and short depressed hairs. The large eyes encroach on the upper surface 

 of the epicranium, and their inner edge is usuall}"- limited by a more or less punctate 

 depression. The vertex, or portion of the epicranium behind the eyes is much 

 broader than the front, and is covered at the sides by the angles of the prothorax ; 

 thus, the eyes notwithstanding their large size are not prominent, and the breadth 

 of the head behind the eyes is as great (or very nearly as great) as it is across the 

 eyes, this being contrary to what exists in the Carabidte, where the greatest breadth 

 of the upper surface lies on a line drawn between the convex portions of the two 

 eyes ; there is no trace of any constriction behind the eyes. In the Colymbetides 

 the surface of the head, when dark in colour, is usually marked by two more or less 

 definite paler spots placed between the eyes, these frequently become united into 

 one, and in Dytiscus are not only united, but placed so as to form an angular mark 

 on the middle of the head ; and in the Hydaticides, the head is usually pale but 

 with dark vertex, and angular dark marks in front, of variable extension according 

 to the species examined. 



The antenna is inserted more or less conspicuously on the undersurface of the 

 head ; the anterior angle of the epicranium being inflexed, the cotyloid cavity for 



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