870 On Aquatic Carnivorous Coleoptera or Dytiscide. 
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 var 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 very 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 coxe ; 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 impossible 
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. 
This group is formed of a single species—Dytiscus dorsalis, No. 630—it has 
the prosternal process more elongate than is the case inany,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 epipleuree 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. 
GRouvUP 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. 
