210 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



hooks. In Pelobius the cilise are nearly entirely absent, the mner edge of the^ 

 maxillary lobe bearing merely two short, fine sette ; in Amphizoa the ciliaj are 

 abundant, and the lower portion of the lobe is furnished Avith dense fine pubescence, 

 while the upper portion bears stouter cilite, a considerable space nearly free from 

 cilise intervening between these two grovips. 



The maxillary palpi are four jointed, the basal joint shorter than any of the 

 others but quite distinct ; the second and third joints arc nearly similar to one 

 another in length ; frequently the third is a little longer than the second ; the fourth 

 joint is a little, or considerably longer than either of the others ; occasionally the 

 terminal joint is notched or emarginate at the extremity (Noterides). The uiaxillte 

 and their palpi are entirely destitute of any pubescence or seta3 (with the exception 

 of the ciliai of the inner lobe). The maxillaj of the Dytiscidte are similar to those 

 of the Carabidae, except in the absence of any outstanding setse and in the less 

 elongate second joint of the palpi ; in this latter respect the Pseudomorphini agree 

 with the Dytiscid*. 



The mentum is a transverse corneous piece, of very hard consistency, articulated by 

 a distinct suture vnih. the piece behind it ; this suture is slighty curved or bisinuate, 

 or nearly straight, but is quite obsolete in Amphizoa : the sides of the mentum are 

 rounded in such a manner that the greatest width is at the base ; in front there is a 

 large piece cut out of the middle for the reception of the ligula, so that the mentum 

 is thus made to consist of two lateral lobes, projecting from a transverse basal 

 piece ; the base of the excision is not straight, but projects farthest forwards in the 

 middle, owing to the excision being deeper on each side in adaption to the piece 

 supporting the labial palpus ; there is thus formed a slightly projecting, more or Itss 

 distinct central lobe at the base of the excision ; this lobe is variable in form, and 

 is usually short in proportion to its width, and with a rounded front edge ; but is 

 sometimes emarginate in front ; when the labial palpi are approximate to one another 

 this lobe is narrow ; or nearly absent {vide Deronectes) and may form a small acute 

 tooth ; such a tooth exists in Noterus but has in that genus a bifid extremity. 

 The side wings or lateral lobes of the mentum vary a little but not much in form ; 

 in Hyphydrus their front termination forms a more acute and elongate angle than 

 it does in other groups. In Pelobius the mentum is very much shorter than in any 

 other Dytiscidee, so that the very broad excision is very short, and the very broad 

 lateral lobes are extremely abbreviate ; in Amphizoa the mentum is remarkable for 

 its large size, the basal transverse piece being very elongate, but in other respects 

 it is formed as in the ordinary Dytiscida^. 



The ligula is large and very conspicuous, it appears externally as a quadrate or 

 transverse horny plate, filling up and projecting beyond the excision of the mentum : 

 its free front margin varies a little in form, it may be nearly straight as in Cybister, 

 or slightly rounded or even very feebly prominent in the middle, so as to be 

 bi-emarginate, and is usually furnished \\ith elongate very fine ciliie, placed some- 



