On Aquatic Carnivorous Coleoptera or Dytiscide. 887 
Besides the relations with Agabus as above mentioned this interesting insect 
shows a great approximation to Platynectes in its systematic characters ; especially 
to the first group of that genus inhabiting Australia and Tasmania, but Ilybiosoma 
is not only of much greater size and entirely different appearance, but has moreover 
the swimming legs incrassate and abbreviate, and the coxal processes much greater 
in the transverse direction, and more separated from one another, and the coxal 
lines more divergent in front. 
I. 48.—Genus PLATYNECTES. (Vide p. 538.) 
This aggregate comprises thirteen species ; the individuals are of rather depressed 
form, often very broad, the surface frequently very shining and polished, and some 
times marked with yellow spots or lines arranged in a symmetrical manner, but very 
variable within the bounds of the same species. The front tarsi of the mate are slender. 
The thorax and elytra are very continuous in outline. The hind coxe are very large, 
and the wing of the metasternum deflexed outside the coxa is a very slender, 
parallel-sided or linear band. The coxal lines are fine, and but little divergent in 
front, and do not reach to the front border of the coxa. The prothorax has a raised 
side margin; the epipleuree of the elytra are quite narrow behind the middle ; the 
swimming legs are either quite slender, or moderately slender, and the hind tarsi 
externally show a slight lobing of the hind margins of the joints. 
The above characters sufficiently distinguish this genus from its allies, with 
several of which it agrees, or approaches, by one or more of its characters. 
The species are found in Australia and Tasmania, Eastern Asia and the Austro- 
Malay islands, and in South America ; and form three tolerably well distinguished 
natural groups, as defined on p. 538; of these three groups the first comprises the 
species least different from Agabus, and the third the most distinct and highly 
developed forms ; the swimming legs in this third group are decidedly thicker than 
in the others. 
I. 49.—Genus LEURONECTES. (Vide p. 546.) 
This aggregate comprises only two dissimilar species, with the following 
characters :— 
Side of prothorax without margin. Hind coxe large, the wing of the metasternum 
deflexed outside it as a very slender parallel sided band. Coxal lines fine, but little 
divergent in front, abbreviate before reaching the front border of the coxa. Epipleura 
quite narrow behind the middle. Swimming legs slender or moderately slender. 
Prosternal process broad, flat and acuminate. 
The two species are closely allied to the third group of Platynectes, but the 
prothorax is without lateral margin. They are different in appearance, one being 
narrow the other rather broad; L. parallelus is a considerably lower form than 
