On Aquatic Carnivorous Coleoptera or DytiscidcB. 871 



The only essential distinction between this and the fourth gi'oup, 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 tibice ; 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 pecuUarly 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. coUaris seems to be a more primitive form than H. oblitus, for it has the 



hind coxse rather smaller, the hind coxal cavities a little more separated, and the 



prosternal process a little lai'ger, while its prothoracic side margin is remarkably 



elevated and distinct. 



Group 8. 



This group consists of five species ; they are small subdepressed insects, almost 



without pubescence, of obscure colour, and rather finely punctate ; the hiud coxal 



cavities are very distinctly separated; and the middle sutural part of the conjoined 



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 agfree in the size of the hind coxse. 



o 



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 



