890 On Aquatic Carnivorous Coleoptera or Dytiscida. 
acute. The prosternal process is very broad, in one species, Agabus sinuatus, it is 
quite flat and almost without margin, in A. pictipennis the basal portion is coarsely 
margined, while in the third species, D. maculatus, the middle portion of the pro- 
cess is slightly convex, and the sides are again flattened out or explanate, and are 
finely margined. In A. sinuatus the coxal lines are not so deep as in the other 
species, and they are rather more divergent in front, and do not quite reach the 
border of the coxa ; in this latter species the epipleuree are not quite so broad as in 
the other two. 
The broad epipleurz are not found in other members of Agabides, but reappear 
in Hyderodes, and in Cybister in a variable manner. 
The geographical distribution is in Europe, Persia, and Japan. 
I. 53.—Genus ILY BIUS. (Vide p. 550.) 
This aggregate comprises twenty-four species, and is characterised by the 
structure of the swimming tarsi wkich have their claws more or less unequal, and 
the basal joints externally with the hind margin (more or less) distinctly lobed. 
Prosternal process very compressed. Inner face of elytra with a tomentose area 
at apex. Side of prothorax margined ; epipleurse narrow behind the middle. 
The species are generally of peculiar shape being distinctly convex longitudinally 
as well as transversely, their sculpture is a reticulation of a fine and dense character 
on the upper surface, and beneath they are finely strigose ; the colour is black and 
pitchy red, and the only pale marks are a spot or dash near the side of the wing- 
case, accompanied bv another near the apex, and sometimes by a marginal yellow 
band. 
The approximation made to Agabus is considerable and is at more than one 
point. The lobing of the joints of the hind tarsi occurs slightly in some of the 
species of the 19th group of Agabus, and the inequality of the hind claws of Hybius 
cinctus is very slight, and not greater than what is found in the male of Agabus 
subtilis, a member of the group of the genus just mentioned. I. cinctus, however, 
does not make any approach to any particular species of Agabus, and the approxi- 
mation between it and Agabus subtilis is an approximation not of the species 
themselves but of the two aggregates of which they respectively form a 
portion. 
The lobing of tlte hind tarsi is greater in some species of Platynectes than it is 
in I. cinctus, but there is no approximation between these two in other respects. | 
This lobing of the hind tarsi is really distinctive of the genus as compared with 
Agabus, for it is greater in Ilybius cinctus (the species of the genus where it is 
least) than it is in any species of Agabus. The inequality of the claws of the hind 
tarsi is also really distinctive between the two aggregates, although as regards 
this the two actually touch by means of A. subtilis and I. cinctus. 
