On Aquatic Carnivorous Coleoptera or Dytiscide. 869 
is sulcate in front; the coxal processes have their middle part projecting quite as 
far as, or a little farther than their outer terminations or angles, but only in a few 
species can the cavities be detected to be at all separated, (see H. clypealis, No. 
508) ; the punctuation of the undersurface is coarse and extensive. 
Some of the species depart shghtly trom the others in the structure of the coxal 
cavities, to approximate in this respect to the first group. And in H. dimidiatus 
the sculpture of the undersurface may be looked on as intermediate between this 
group and the third group; the species just named also approximates the third 
group by the structure of its tarsi. Both in this and the preceding group the coxal 
lines are usually remarkably sub-parallel, strongly elevated, but little separated in 
their anterior portions, and very little divergent at their termination; but these 
characters are not absolutely constant, for H. hybridus, Aubé (No. 519), has the 
lines rather widely distant in front, and rather abruptly approximated about the 
middle of their course; also in it, and still more in H. dimidiatus, they show an 
undoubted, though never conspicuous, divergence in their terminal portions. In 
the two groups the apices of the processes never assume, even in an incomplete 
manner, the form of rounded lobes, but are truncate, or approximating thereto, and 
their outer angles are nearly acuminate. 
Grovp 3. 
This group includes about thirty species, of variable form and size, but all have 
the upper surface variegate ; the hind coxal cavities are quite approximate or very 
nearly so, and the coxal processes do not on the mesial line extend quite so far 
back as at their outer portion, and so do not present a common straight hind margin, 
but assume more or less decidedly the form of separated lobes. The species are 
distinguished from those of all the other groups of Hydroporus (except group 9) 
by the rounded form of the coxal processes; those arranged at the commencement 
of the group show this character only in a slight degree, and resemble the species of 
the fourth group of Deronectes : also the earlier species have the third joint of the 
front tarsus but little lobed, while the terminal one is more elongate than in the 
species towards the end of the group. 
Group 4. 
This group includes about eighty species ; in it the hind coxal cavities are quite 
approximate and the lamina dividing them quite concealed ; the coxal processes 
are soldered together quite to the hind margin, so as to present a common, truncate 
extremity ; and their outer angle formed by the short coxal border is only very 
slishtly rounded or obtuse ; if the common suture at the hind margin is a little 
more prolonged backwards, yet it is only very slightly so, and the projecting portion 
is not at all adpressed to the level of the ventral segments. The prothorax is with- 
out any longitudinal stria or depression at the side. 
5 T 2 
