On Aquatic Curnivorous Coleoptera or Dytiscide. 903 
I. 65.—Genus HY DERODES. (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 the hea and the side of the thorax yellow; the form 
is rather broad and short, moderately convex. 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 coxee 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 coxal 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, 
nearly 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 differmg 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 tibize 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 trom 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 tibize are much more imperfect, and the clypeal suture is more obliterated 
