200 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



which is confined to them ; and the spaces between the grooves are without 

 punctuation, while in the males all the surface is punctate ; the females of the 

 difterent species of this genus differ much in their characters from one another as 

 to the development of the grooves and the punctuation and pubescence, and in 

 Dytiscus sulcatus (of the genus Acilius) we find a patch of pubescence occupying a 

 depression on each side of the prothoras. 



In Thermonectes the surface is highly polished, and when the females possess a 

 sexual sculpture, it consists of beautiful elongate punctures placed on the basal part 

 of the wing-cases but not extending over a large part of their area. In Sandracottus 

 the surface is very highly polished and the female is destitute of sexual sculpture. 

 In Graphoderes the females are usually destitute of any sexual sculpture, except a 

 slio-ht corrugation of the surface on each side of the prothorax, but in this genus 

 we meet occasionally with a more extreme development of sexual sculpture 

 than any found elsewhere in the Dytiscidee or indeed in the whole of the order 

 Coleoptera, the surface of the wing-cases being rendered rough by a very coarse 

 sculpture almost like tubercles (but not very different from what exists in 

 Hyderodes) while the prothorax is covered with beautiful deep corrugations ; these 

 exceptionally sculptured females are very rare and it has been thought they were 

 only a second form of that sex in a species (D. zonatus) having usually smooth 

 females, but I think more probably they belong to one or two distinct species of 

 the genus. 



The Hydaticini are insects with a very smooth surface, and many species are 



without sexual sculpture, but others exhibit such well marked ; in this group the 



chief seat of the sculpture is a portion of the area of each side of the thorax, but 



sometimes also it is situate on the basal portion of the wing-cases ; it consists usually 



of coarse, short, irregular impressions, but little connected with one another, and 



sometimes there exists on certain individuals {vide in Dytiscus goryi No. 1020) 



only one or two such impressions ; in a few New World species however the sexual 



sculpture consists of a circumscribed, and remarkably well defined patch of quite 



fine sculpture on each side of the thorax, formed by very closely placed fine rugae 



{vide H. subfasciatus No. 1019). in the Cybistrini there is frequently present in 



the female, a highly developed sexual sculpture, consisting of fine anastomosing 



scratches, which frequently nearly cover the entire upper surface of the insect, but 



in other cases are restricted to a much smaller area, sometimes this sculpture is 



more developed on the thorax than it is on the elytra, while at other times we find 



the reverse of this ; in many species of Cybister there frequently exists a sexual 



sculpture so fine and slight that it can only be detected by a careful examination, 



and many females are quite smooth ; in this genus, great variation of the sexual 



sculpture is quite common in certain species : some species of Megadytes {vide M. 



steinheili No. 1108) show a most beautiful sexual sculpture, the prothorax being 



quite smooth, in great contrast to the wing-cases which are covered, at any rate on 



