On Aquatic Carnivorous Coleoptera or Dytiscidce. 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 male are slender. 

 The thorax and elytra are very continuous in outline. The hind coxse 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 epipleurse 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 comjji'ises only two dissimilar species, with the following 

 characters : — 



Side of prothorax without margin. Hind coxse 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 difterent in appearance, one being 

 narrow the other rather broad ; L. parallelus is a considerably lower form than 



