868 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



(in the length between the hind margin of the posterior coxpe, and the second 

 ventral segment), so that their terminal portion is very narrow, although in some 

 species it remains quite di?tinguishable till as far, at least, as the commencement 

 of the last ventral segment, (Dytiscus depressus, No. 472, &c.) ; while in others it 

 cannot be distinguished after the second ventral segment is passed (D. griseostriatus, 

 No. 493, &c.); the difference between these two forms is however not great, and 

 intermediates occur. There is no ligula on the inner face of the elytra near the 

 apex ; the genicular area of the epipleura is generally indistinct, and is never 

 limited externally by a raised line ; the swimming legs are but slender, their femora 

 are never incrassate, and their postero-external angle is never acute. The hind 

 coxee are not large, their front border having but litt'e extension in the anterior 

 direction, and the culmen of its arch is rather rounded and broad, thus contrasting 

 with Coelambus : the hind articular cavitie.s are contiguous or nearly so. 



The species are found in the European and Mediterranean regions, but one or two 

 exist in Nortli India and Abyssinia and Arabia, and one or two others in the 

 northern portion of the New World. 



I. 41.— Genus HYDROPORIJS. {Vide p. 435.) 

 Group 1. 

 The first group of species included in Hydroporus consists of certain insects dis- 

 playing a slight peculiarity in the structure of the apices of the coxal processes ; 

 the middle portion of the apex being slightly prolonged, so that the articular 

 cavities are distinctly separated by this middle portion ; which is closely adpressed 

 to the plane of the ventral segments. Six species are included in the group ; they 

 all have the third joint of the front tarsi strongly bilobed, and the general 

 characteristics are much those of the following group ; the punctuation of the under 

 SLU'face is sometimes but little developed, and never very coarse, the wing-cases are 

 •. ariegate in colour, and the undersurface is never black, though sometimes greatly 

 in'"useate The species are all rare, and have therefore been but imperfectly examined ; 

 one of them, (Hydroporus vittatipennis, No. 500), is perhaps not very naturally 

 associated with the other species, for the lateral margin of its prothorax is extremely 

 slender, even in front, while in all the other species it is more or less flattened and. 

 thickened in front. 



Group 2. 



In this group the front tarsi have the third joint more deeply bilobed than is the 

 case in the following group ; (in some species however the distinction is but slight 

 in this respect, see Hydroporus dimidiatus, No. 517) ; the thoracic side margin is 

 usually thickened and flattened in front, but to this also there are exceptions (see 

 H. mellitus, No. 502, and H. hybridus. No. 519). The wing-cases are variegate but 

 occasionally ():'ly obscurely so; the undersurface is red or yellow; the metasternum 



