On Aquatic Carnivorous Coleoptera or Dijtiscidoe. 419 



Group 1. (Species 450 to 461). 



Swimming legs very slender, their tarsi slender and elongate, very distinctly 

 longer than the tibiao ; the latter with the lower face densely punctured ; prosternal 

 process narrow, carinate along the middle, often much compressed laterally, never 

 quite flat, its form more or less obscured by fine setae ; elytra not denticulate near 

 the apex; surface of body very dull, the upper one bearing a more or less distinct 

 bloom or tomentum, which is very easily removed by friction ; the surface uni- 

 colorous, or nearly so, always destitute of any definite marks or pattern ; sexual 

 disparities in legs and feet scarcely to be detected, but often very remarkable as 

 to the form of the prothorax. 



The species are about twelve in number, and are all found in clear runnino- 

 streams in the European and Mediterranean region. 



Group 2. (Species 462 and 463). 



Hind coxae distinctly separated by a partition projecting backwards beyond the 

 coxal cavities ; hind tibiae densely and finely punctured on their infero-external 

 aspect, but allowing the series of punctures near the edge to be seen ; prosternal 

 process remarkably broad and flat, without central carina ; colour of surface variegate. 



The species are only two in number; and both are European. 



Group 3. (Species 464). 



Hind tibiae coarsely punctate on the infero-external face, with, however, the 

 marginal series of punctures visible at the upper edge of the punctuation : hind 

 coxal cavities not visibly separated ; elytra with a vague yellow pattern ; prosternal 

 process not very broad and flat. This species is found in the Canary Islands. 



Group 4. (Species 465 to 494). 



Hind tibiae with their infero-external face glabrous, and shining ; hind coxal 

 cavities not visibly separated, prosternal process neither large, nor broad and flat, 

 elytra always variegate with yellow or red. 



This group comprises the greater number of the species of Deronectes, and they 

 will be arranged according to whether the elytra have a minute sharp denticle 

 near the extremity, or are without such denticle. This is not a very good character 

 as there are a few sjaecies in which the denticle is very obscure, and some others 

 in which it is distinct in one sex, and less so in the other ; if however a careful 

 examination be made the observer will not have much difficulty in decidino- to 

 which of the two categories he should refer the individual under examination. 



A, elytra with a denticle near the extremity : species 465 to 484. 



B, elytra without a denticle near the extremity : species 485 to 494. 



TRASS. nOY. DCB SOC, N.S., VOL. II. 3 I 



