On Aquatic Carnivorous Coleoptera or Dytiscide. 871 
The only essential distinction between this and-the fourth group, is the separa 
tion of the hind coxal cavities ; although this is but slight yet when it is appreciated 
and examined it is found to be a valid difference: the separation is least distinct in 
H. ferrugineus (No. 636), and that species departs from the others by its more 
elongate anterior tibize ; in the other species the front tibiae are remarkably short 
and broad. 
All the species of the group inhabit springs and small rills, sometimes of very 
cold water, in mountainous or hilly districts. 
Group 7. 
The three species forming this group have the hind coxal cavities very distinctly 
separated, and differ from the sixth group by the peculiarly large prosternal process, 
the wing of the metasternum is bent back so as to form a very short band between 
the coxa and the epipleura: the males have the front tibia emarginate below the 
knee. 
From the eighth group the species are distinguished by the peculiarly large 
prosternal process ; this is of an elongate-oval form, nearly flat, but very distinctly 
margined at the sides, and only moderately acuminate at the tip. 
H. collaris seems to be a more primitive form than H. oblitus, for it has the 
hind coxee rather smaller, the hind coxal cavities a little more separated, and the 
prosternal process a little larger, while its prothoracic side margin is remarkably 
elevated and distinct. 
Grovr 8. 
This group consists of five species; they are small subdepressed insects, almost 
without pubescence, of obscure colour, and rather finely punctate ; the hind coxal 
cavities are very distinctly separated; and the middle sutural part of the conjoimed 
coxal processes projects farther backwards than their outer angle ; this latter is not 
at all rounded; the anterior border of the hind coxa takes a considerable forward 
extension, so that externally the coxa is much more elongate than it is in the middle ; 
the prosternal process is short, broad in proportion to its length, not compressed, 
but flat, and more or less distinctly carinate along the middle. The different species 
do not agree in the size of the hind coxe. 
Group 9. 
This group comprises five species, and is distinguished by the development ot 
the coxal processes into free lobes, approximating to what we find in the Agabini. 
The wing-cases are not variegate in colour. The mesial line of the conjoined coxal 
processes is shorter than the coxal lobes, and the outer angle of each of these is 
rounded or obtuse. 
This large aggregate, Hydroporus, is composed of about one hundred and sixty 
species, arranged in the nine groups already characterized and discussed, and is the 
