534 On Aquatic Carnivorous Coleo2')tera or Dijtiscidce. 



of the male, while the females before me from Lago Pinter, .seven in number are 

 all similar to the males. There thus appear to be two Alpine races, the males of 

 the two being similar while the females are very different. The species however 

 not only varies in sculpture both absolutely (that is in both sexes considered together) 

 and sexually, but it .shows quite as great and even more interesting modifications, 

 in what may be called quite structural characters; thus the shape becomes in the 

 Alpine forms very different from what obtains in the plains, and in correspondence 

 with this modification of shape is a change in the legs, which are very much more 

 elongate and slender, (that is less highly developed for swimming) than they are 

 in the individuals of the plain ; this diminution in the power of the legs reaches its 

 extreme in the most divergent females of both the Aljiine forms. 



The male tarsi are subject also to much variation, the amount of their incrassation 

 and the sexual structure of the front claws being each inconstant ; the greatest 

 development of the male feet and claws is found in the large individuals of the 

 plains, the smalle.st in the Alpine forms ; in these latter the amount of dilatation of 

 the tarsus is greatly diminished, and the posterior of the claws on the front feet 

 becomes more slender, the dilatation of its hinder edge lieing in extreme cases very 

 greatly diminished : the front claws moreover are variable independently of Alpine 

 or boreal localization, for I have a male (from Cor.sica ?) in which the anterior claw 

 retains pretty nearly the normal shape, but is not longer than the front one. 



It seems very difficult to comprehend these vai'iations. Especially peculiar seems 

 the fact that the males of Alpine and boreal districts depart from the dwellers of 

 the plains in one direction only, and yet their females depart in two opjiosite 

 directions ; equally difficult of explanation is the fact that though disj^arity in 

 sculpture of the sexes is the rule, yet this disparity disappears in the two forms 

 which in other respects are most widely different from one another, viz., the large 

 and powerful South European variety, and the feeble, nionomorphic Alpine variety", 

 we seem however at any rate justified in inferring that the peculiar sculpture of the 

 females bears no correlation to the development of the male tarsi. 



Group 21. 



Anterior portion of prosternum united uuth prosteriial process so as to form a 

 sensible angle ; prosternal process compressed : wings of metasternum rather short ; 

 coxal lines not greatly turned outwards at the extremity ; coxal border small ; 

 male anterior tarsi much developed ; hind legs slender. 



Two Palsearctic species. 



