200 On Aquatic Carnworous Coleoptera or Dytiscide. 
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 
different 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 
depressicn on each side of the prothorax. 
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. 
slight 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 Dytiscidze or indeed in the whole of the order 
Coleoptera, the surface of the wing-cases being rendered rough by a very coarse 
sculpture almost lke 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 (wide 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 rugz 
(vide H. subfasciatus No. 1019). 1n 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. 
