On Aquatic Carnworous Coleoptera or Dytiscide. 197 
sculpture of the two sexes ; thus in Dytiscus parallelogrammus (No. 416) the female 
differs from the male in that the punctuation is very much finer and less deep and 
the surface is dull, and on examination with a considerable power of the microscope 
it is seen that the dullness arises from the surface being covered with a very dense 
minute sculpture of a peculiar character, but a good deal similar to that which is 
seen on a larger scale in Meladema coriacea (No. 978). In another species of 
Ceelambus (Dytiscus impressopunctatus No. 409) the phenomena are quite different ; 
here the female usually resembles the male in sculpture except that its punctuation 
is a little denser and finer: there occurs however very rarely a second form of the 
female (Dytiscus lineellus Gyll.) very different from the male, the surface being 
much more finely punctured and dull, and on examination with a considerable 
power of the microscope it is seen that the dullness arises from the surface being 
covered with an extremely fine obsolete sculpture of a reticulate nature such as is 
seen in Agabus. In the large genus Hydroporus the females frequently differ in 
sculpture from the males in a more or less conspicuous manner, and the difference 
is sometimes dimorphic (vide Hyphydrus memnonius No. 558). In the Agabini 
we find in the genus Agabus that sexual differences of sculpture are of frequent 
occurrence: the differences is sometimes slight as in the case of Dytiscus guttatus 
(No. 670) where the female has the sculpture a little coarser than in the male; or 
it may be very considerable as in A. lecontei and A. griseipennis (No. 731 and 
732), where the male is less but the female is more reticulate than is usual in the 
genus ; or the sexual differences of sculpture may be variable as in the cases of 
Dytiscus congener (No. 706), and Dytiscus bipustulatus (No. 751), and in these 
cases the variations seem to be, to some extent at any rate, dependent on the 
locality the specimens inhabit. 
In the genus Copelatusa difference in the sculpture of the two sexes is very fre- 
quent, and the differences are in some species very great, in others only slight, and are 
quite as frequently found on the surface of the prothorax as on the wing-cases ; 
they usually consist of very short linear impressions, or fine, rather irregular scratches, 
dimorphism of the females is occasional, and when it exists 1s strongly marked, the 
female being either similar to the male in sculpture, or having a large area of the 
surface covered with an additional sculpture (vide Copelatus neglectus No. 841). 
It should be remembered that this genus is unique among the Dytiscide by 
reason of the existence in it of a remarkable sculpture common to the two sexes: 
this non-sexual sculpture is of quite a similar nature to the sexual sculpture of other 
genera: the impressions on the thorax of Colymbetes sulcipennis (No. 895) and 
the regular grooves on its elytra are just such as would (from what exists in the 
females of other genera) make one suppose them to be a female sexual sculpture, 
and yet they are equally developed in both male and female ; it is further interest- 
ing to note, that the females of the species I am alluding to (and of other Copelati) 
have an additional sexual sculpture consisting of some extremely fine irregular 
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