On Aquatic Carnivorous Coleoptera or Dytiscide. 201 
their basal portion, with regularly placed elongate impressions; the largest of the 
Dytiscidee, viz., Cybister giganteus No. 1117 and Megadytes ducalis No. 1118, have 
no sexual sculpture whatever: in Homeodytes we find the females of two species 
to possess a most excessively fine sexual sculpture, consisting of extremely delicate, 
short scratches, giving rise to a silky appearance on the basal part of the elytra. 
From this imperfect review of the sexual sculpture of the Dytiscide it will be 
gathered that much variety exists as to its character, and as to its degree of 
development, and that the occurrence of two forms of the female of a single species 
is not unfrequent in various portions of the family: there is considerable reason to 
‘suppose that the development of the sexual sculpture is to some extent connected 
with local and climatic conditions, and it may prove to be that it is of more frequent 
occurrence in temperate and cold climates than in warmer ones: if it serves any, or 
what purpose is still undetermined, but it is certainly amongst the most interesting 
peculiarities of the Dytiscidze, and of considerable importance in respect to its 
bearings on the questions of sexual variation and selection. 
The peculiar sculpture of the species of Copelatus is of much interest and well 
deserving investigation. In some of the higher forms of the genus (Col. sulcipennis, 
Lap. e.g.) it appears as very deep and regular striew or grooves, to the number of 
10, 11, or 12 on each wing-case, and extending nearly their whole length, but 
becoming finer at the extremity, where usually some of them are more abbreviated 
than others. In other species no trace of such striation can be detected ; but in 
ome of these cases the fine punctuation of the wing-cases assumes the form 
of very short fine scratches, which while they may be very distinct in the female, 
can sometimes scarcely be traced in the male (C. simplex, Clk.) ‘the scratches 
displayed in such cases frequently assume a different direction on the hinder portion 
of the wing-case, becoming transverse there, when they have a longitudinal direction 
in front (Celina australis No. 806) ; while in some other species only the transverse 
posterior scratches exist (as in C. ferrugineus). 
In some of the cases where the elytra are truly striate, z.e. display elongate 
regular straight lines, it can be perceived that these are developed along the series 
of impressed punctures which are so constant a feature of the Dytiscidee ; this is 
not the case in those species, where the scratches are short, for they are not then 
more developed near the series of the punctures than they are elsewhere ; so it 
would seem there are as regards the sculpture three different series of species, viz., 
1, punctuation ordinary; 2, punctuation elongate, and diffuse; 3, punctuation 
elongate, but only along the lines of serial (and secondarily of the interserial) 
punctures; the punctuation of this latter category becoming in the most differentiated 
cases, highly developed symmetrical striz. 
It seems impossible to believe that the development of this beautiful sculpture 
can have been determined by the action of natural selection ; preserving those 
individuals of a species in which it was more developed than in others, for in 
