On Aquatic Carnivorous Coleoptera or Dytiscidce. 903 



I. 65.— Genus HYDERODES. {Vide -p. 633.) 



Three species, very similar to one another, form this genus in its present condition. 

 They are of moderate size, between half and three quarters of an inch in length ; of 

 dark colour with the front of *:he head and the side of the thorax yellow; the form 

 is rather broad and short, moderately conA^ex. The suture between the clypeus 

 and the front can be seen at the sides, but is quite obliterated in the middle. The 

 prothorax has a thickened lateral margin. The prosternal process is acuminate, 

 and rather elongate, not compressed, its anterior half distinctly margined, its 

 posterior half quite without margin ; the inter-coxal process of the metasternum 

 bears an elongate deep groove for its reception. The hind legs are moderately well 

 developed for swimming, rather elongate, comparatively little thickened, the hind 

 margins of the joints of the tarsi are scarcely lobed externally, the claws are rather 

 short, curved, and of about one length. The hind coxse are moderately large, their 

 front border is only moderately arched, the wings of the metasternum are rather 

 small. The coxal lines are very little curved, and the elongate coxal border is 

 nearly straight ; the coxal lobes are very elongate, prominent, their apical portion 

 extends a good deal more backwards than the cosal notch, and is obtuse, the coxal 

 notch is elongate. The side piece of the fourth ventral segment is of moderate 

 breadth, about one-third as broad as it is long ; the abdominal stigmata are large, 

 the penultimate one a good deal broader than the preceding one, but not twice as 

 broad as it, the last stigma transverse, moderately developed. The male front 

 tarsi have the three basal joints greatly dilated, so as to form a moderately large, 

 nearlv circular saucer, the fourth joint quite undilated, short, the fifth elongate, 

 about as long as the three basal ones together ; the saucer is furnished beneath 

 with eighteen or twenty large palettes, not differing greatly from one another in 

 size. The three basal joints of the middle tarsi are considerably dilated to form a 

 kind of oval plate, which bears beneath several rather large palettes. The tibiae of 

 the anterior legs of the male are rather thick, and their posterior aspect is obliquely 

 truncate, or shaved off, to allow the dilated tarsus to turn back behind the tibia ; 

 this truncation does not extend half way up the tibia, and when the leg is looked 

 at from the front, the only trace of it that can be seen, is a kind of emargination, 

 or interruption of the outline of the lower part of the external face of the tibia. 



The species are as yet found only in Australia and Tasmania, and I expect they 

 will prove to be essentially Tasmanian, and to have extended into Australia at a 

 comparatively recent period of their history. 



Although the true position of this interesting genus has not yet been understood, 

 there can be no doubt that it should be placed near Dytiscus, and also that it shows 

 no other approximation. It cannot however be considered to be very near to 

 Dytiscus : the terminal abdominal stigma is much less developed, the male front 

 tarsi and tibiae are much more imperfect, and the clypeal suture is more obliterated 



