908 On Aquatic Carnivorous Coleoptera or Dytiscide. 
for fully half the length of the tibia, and is parallel or subparallel to its outer 
border. 
The intermediate femora bear quite short sete. The terminal abdominal stigmata 
are of moderate size. The male front tarsi have the three basal joints dilated into 
a circular plate ; this bears large palettes beneath, and of these the three or four 
basal ones are distinctly but not greatly, larger than the others ; the basal fringing 
hairs are present (except in one or two species); the middle tarsi have the three 
basal joints distinctly, or even broadly dilated, and bearing beneath distinct 
round palettes ; when the females have a sexual sculpture, it consists of some rug 
on each side of the thorax ; these rugee may be coarse and sparse, or very fine and 
indistinct and dense. 
The species are distributed over the warmer parts of the Old and New Worlds 
and Australia, and one group of a few species is peculiar to the northern or tem- 
perate parts of Europe and North America, with the exception of one of its species 
which occurs in Australia. 
f. 69.—Genus ACILIUS. (Vide p. 672.) 
Six species are united to form this rather heterogeneous aggregate. The formis 
rather flat above, and the outline continuous, the surface is punctate above and 
below, the head and prothorax being however in some species smooth. The pro- 
thorax is without any lateral margin. The prosternal process is variable, but is 
never very elongate or acuminate at the apex ; the middle coxe are rather widely 
separated, and the impression on the apex of the inter-coxal process of the meta- 
sternum is a broad, short, shallow, rounded depression. The hind cox are 
extremely large, their front border is very arched, and the wing of the metasternum, 
much curved and deflexed outside the coxa, is dilated a little before the termination, 
its extreme apex being however somewhat acuminate. The coxal lines although 
subobsolete can always be distinguished in the posterior part of their course, and 
they there mark off a distinct supra-articular border, which is never very broad, 
and always acuminate or attenuate at its termination behind. The coxal lobes are 
rounded and short, and there exists only an obscure trace of the coxal notch. 
The swimming legs are well developed, but not very incrassate, and are terminated 
by two nearly straight claws of which the inner is about twice as long as the outer 
one: the spurs of the tibiz are distinctly emarginate at the apex. The epipleure 
are variable in their width, but are never very narrow at the shoulders. The front 
and middle femora bear a few, elongate, rigid setze on their lower margin. The 
terminal abdominal stigmata seem rather well developed. The sexual characters 
are variable, but the front tarsi of the males are highly developed, and the plate 
formed by the dilated three basal joints is surrounded with beautiful fringing hairs, 
and bears beneath three large palettes (one of them very large, but the other two 
