886 On Aquatic Carnivorous Coleoptera or Dytiscidcs. 



genus Ilybius : moreover D. serricornis has the structure of the wing-cases similar 

 to that which exists in Ilybius ; on their inner face the marginal line is scarcely to 

 be detected, but at the apex it is replaced by a tomentose area (this not so largely 

 developed however as in Ilybius) ; whether this character exists in the other species 

 of the group I am unable to say. The approximate coxal lines and the consequent 

 form of the coxal lobes are somewhat similar to what is found in Copelatus, to 

 which aggregate however this group shows no other approach, indeed it is more 

 distinct therefrom than is any other group of the genus. 



Group 23. 



Under-wings reduced to subclavate slips, which are insufficient for flight ; 

 sculpture of elytra consisting of isolated scratches, of which the basal ones assume 

 an oblique, the outer and apical ones a transverse direction. 



The reduction of the wings is most remarkable and has but few parallels in the 

 rest of the carnivorous water-beetles ; I have examined a specimen of each sex, for 

 in the individual where I first observed the fact I thought the occurrence of so 

 abnormal a structure must have been a mere deformity. Except for this character, 

 and the absence of a coxal file, the species would come very near to group 8 by 

 most of its other characters. 



I. 47.— Genus ILYBIOSOMA. {Vide p. 537.) 

 This is an autogenus ; the insect is of the size of the larger Agabi, of dark colour, 

 and with convex upper surface, so as to approach somewhat in form to Ilybius. 



The outline of thorax and elytra is continuous ; the lateral margin of the thorax 

 is broad and subobsolete, being but little raised, and at the posterior angles nearly 

 effaced. The prosternal process is elongate, convex transversely but not compressed, 

 its side finely margined, the margin not extending to the extremity. The coxal 

 processes are largely developed in the transverse direction, and much separated 

 from one another ; the coxal border is narrow, the coxal lines are a good deal diver- 

 gent in their anterior portion, but they arc abbreviated before reaching the front 

 border of the coxa. The short stout hinder tarsi have a slight lobing of the 

 hinder margins of the basal joints on the outer side. Hind coxas largely developed, 

 with greatly arched upper border ; the short wings of metasternum greatly deflexed 

 in consequence ; swimming legs thick and abbreviated ; epipleurse behind the 

 middle narrow. 



Agabus regularis, Lee, which possesses the above characters has much the appear- 

 ance of the large species of the 1 9th group of Agabus ; but the linear form of the wings 

 of the metasternum is much more conspicuous, and the s\vimming legs are thickened 

 and abbreviated. It perhaps is less widely separated from Agabus politus and A. 

 gagates, than it is from any other species known to me. It inhabits North America. 



