902 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



I. 64.— Genus JJELADEMA. {Vide p. 631.) 



Two species are all that are at present known to form this aggregate, but they 

 are far from closely allied, and will perhaps have to be separated. They are of 

 large size (20 m.m. or more long), one of them is very black in colour, and its wing- 

 cases bear a very peculiar sculpture, giving them an appearance as if they were 

 covered with overla2:)ping scales ; the other species has the wing-cases yellowish, 

 speckled with black after the manner of Rhantus, and in it the peculiar sculpture 

 of the other species remains undeveloped, although on careful examination some 

 riidimentary signs of it can be detected. The prothorax is without lateral margin. 

 The side pieces of the fourth and following ventral segments are very narrow ; the 

 metasternal groove is moderately well developed ; the hind tarsi are elongate, their 

 terminal joint distinctly longer than the preceding one. The prosternal process is 

 rather narrow and compressed, and the metasternal groove for its reception is distinct 

 but narrow. The wings of the metasternum are not so large as in Colymbetes, but 

 their termination in Dytiscus lanio (No. 979), is more slender than in the genus 

 Scutopterus. The hind coxse are not very large. The swimming legs are long and 

 slender, their femora with the lamina at the outer angle very little developed, and 

 it angle indefinite and obtuse ; their tarsi have the hind margins of the joints but 

 little lobed externally. The penultimate abdominal stigma is moderately large. 

 The male tarsi beai' palettes beneath and their claws are elongate. 



The aggregate seems to be quite distinct both from Rhantus and Colymbetes ; 

 although in respect of the metasternal groove it is intermediate between the two, in 

 other respects this is not the case. It is distinguished from Rhantus by the slender 

 swimming legs, with less developed femora, by the narrower metasternal groove, 

 and by the more transversely elongate penultimate abdominal stigma. It shows 

 no approach to those species of Rhantus (Colymbetes capensis, No. 957), &c., which 

 like itself have the thorax without a lateral margin; nor is there any other species 

 of Rhantus which specially approximates it. 



From Colymbetes it is discinguished by the better developed metasternal groove, 

 by the little lobed hind margins of the posterior tarsi, and their longer terminal 

 j oint, as well as by the different sculpture and by the male tarsi and. claws. 



Although there are but two species in the aggregate, they are so different that 

 they must be considered representative of two groups, viz.: — 



1. Meladema coriacea. — Anterior border of hind coxa scarcely at all arched exter- 

 nally ; elytra with intricate sculpture. 



2. Dytiscus lanio. — Anterior border of hind coxa a good deal arched externally, 

 and the termination of the wing of metasternum slender : elytra shining, 

 with obsolete tubercles. 



The species of the first group inhabits southern Europe, and the Canary Islands; 

 "while that of the second group is peculiar to Madeira ; where it is probable there 

 is more than one species. "WoUaston indeed has already' described a second which 

 remains unknown to me. 



