On Aquatic Carnivorous Coleoptera or Dytiscide. 921 
an oval, attenuate behind, but varying from extremely short to elongate ; the upper 
surface may be punctate, but is usually excessively polished, the wing-cases are 
variegate, or not so; the prominent platform of the breast is nearly always very 
coarsely punctured. The antennze show no remarkable developments; the front 
tibize have the outer margin rounded and densely set with short regular ciliz, the 
outer apical angle has completely disappeared ; moreover the tibia is narrowed to- 
wards the apex, and on its posterior face isa large cavity in which is inserted a thick 
curved spur ; owing to the attenuation of the tibia, this spur has often the appearance 
of being an actual prolongation of the tibia. The anterior coxze are always a good 
deal separated from one another, the anterior transverse band of the prosternum is 
in front of the coxze moderately long, the prosternal process proceeds backwards 
from this band from an almost insensible point of departure, and behind the cox» 
becomes greatly broader (Hydrocanthus) or gently broader (Canthydrus) and 
its posterior margin is truncate, or only very obscurely a little longer in the 
middle. 
The coxal processes are greatly prolonged backwards, and their terminal angle is 
rendered acute by a group of rigid ciliz. The swimming legs are either moderately 
or greatly developed ; their femora have at the extremity of their hind margin a 
very highly developed group of cilize ; the face of the femur is either traversed by 
a series of punctures parallel to, but at a distance from, the hind margin (Hydro- 
canthus), or placed so very close to the margin as to give the appearance of the 
hind margin itself being ciliate (Canthydrus). 
The Hydrocanthini are distributed over the warmer parts of the world ; in the 
European region they do not extend north of the Mediterranean, and in the Ameri- 
can are found at any rate as far north as Massachusetts. 
So far as regards the distinction of the species, the Hydrocanthini are amongst 
the most difficult of insects to deal with ; the species however, notwithstanding 
their extreme similarity, will be found, I have no doubt, to be really distinct, 
and probably will prove to be much more numerous than is at present 
anticipated. 
IJ. 4.—Group Varetuni. (Vide p. 282.) 
This group comprises only nine species, arranged in three genera, two of which 
are autogenera. They are insects of rather small size, (from 3 to 8 m.m. in 
length) ; of Hydroporoid appearance, but with the outline of the body much more 
interupted at the junction of the thorax and elytra than is usual in the Dytiscide ; 
the front and middle legs are elongate, and the front tarsi are peculiarly elongate 
and narrow in some of the species. The head is very short in front of the large 
and prominent eyes ; the prosternal process is very abruptly bent, and does not 
connect with the metasternum, but its point terminates in front of the middle coxe, 
between which it is concealed ; the middle coxze are exposed, and prominent, and 
