870 ■ On Aquatic Carnivorous Coleoptera or Dytiscidce. 



The group is a very natural one formed by closely allied species, in no one of 

 ■which have I been able to detect any important structural distinction from the 

 others. The chief variations of structure are to be found as follows : 1st, in the 

 prosternal process, which in H. modestus and the species iicar it is more elongate 

 than usual ; and is also either much compressed laterally, and so appearing narrow 

 — the case in most of the species of the group — or is little compressed and broad, 

 as in H. arcticus ; 2nd, in the third joint of the front and middle tarsi, which is 

 either comparatively large with xerj elongate sub-lobes (Dytiscus modestus, No. 

 627), or is small and obscurely lobed, (Hyphydrus pubescens. No. 568, &c.) ; and 

 3rd, in the amount of extension forwards of the front border of the hind coxsa ; this 

 is very slight indeed in some species {e. g., Hyphydrus memnonius, No. 558 and 

 Hydroporus sibiricus, No. 583), so that the coxa is no longer externally than it is 

 along the mesial line, and the culmen of the arch is very broad and low ; in other 

 species the anterior extension may be a little greater (<?. (/., Dytiscus planus, No. 

 575, Hydroporus modestus. No. 627) so that the coxa is distinctly longer externally 

 than it is near the middle, and the culmen of the arch more abrupt. It is impcssible 

 however to make use of these characters to tabulate the species, and I cannot make 

 any divisions that would facilitate the naming of the species without leading to 

 error. 



Group 5. 



'I'his group is formed of a single specie-s — Dytiscus dorsalis, No. 630 — it has 

 the prosternal process more elongate than is the case in- any member of the fourth 

 group ; and its head has in front a margin, bent down over the labrum, entire 

 throughout, and so allowing an uninterrupted transverse depression to be seen over 

 the labrum — this character is peculiar to it amongst the allies — ; to these may be 

 added a peculiarity of form, the thorax being a little curved at the sides, and 

 scarcely broader behind than in front ; the mesosternum is placed at a greater angle 

 with the metasternum than usual, so that it is a little more visible between the 

 latter and the thorax ; and the shoulders of the epipleurae are only gradually and 

 slightly bent inwards ; the epipleura indeed throughout its whole length is less 

 sharply defined than usual. 



Hydroporus kohlstromi, Sahl. (No. 629), agrees with this species in many respects 

 but has not the depression over the labrum. 



Group 6. 



This group comprises six species ; they are very little pubescent, and not 

 variegate ; and have the posterior coxal cavities slightly, but distinctly, separated ; 

 the hind coxa is but little longer externally than it is along the mesial line, the 

 metasternum forming only an obscure band outside the coxa, or the band indeed 

 may be entirely wanting ; the prosternal process is narrow, compressed laterally, 

 and acuminate at the tip. 



