892 ; On Aquatic Carnivorous Coleoptera or Dytiscide. 
I. 54._Genus COPELATUS. (Vide p. 562.) 
This is an extensive aggregate, comprising more than ninety species; they are 
rather flat insects with a very continuous outline; and are oval or oblong-oval in 
form ; the colour is variable, frequently unicolorous black, while not unfrequently 
there is a yellow basal band on, and a pale extremity to, the wing-cases ; the size 
is frequently quite small and the greatest length attained is 10 m.m. of length: the 
sculpture of the upper surface is remarkable and usually consists of regular limes, 
which frequently form elongate strize on the wing-cases, but sometimes are abbreviate 
and broken up, and sometimes are quite wanting ; the upper surface of the pro- 
thorax frequently bears short irregular scratches. The coxal lines are peculiar, 
being extremely close to one another, so that near their divergence at the coxal 
lobes they are almost contiguous with the longitudinal line dividing the two coxee ; 
moreover at the anterior part of the coxal lobes they become excessively fine, so 
that they can with difficulty be detected, and are abruptly turned outwards at right 
angles to their former direction. These peculiarities of the coxal lines are quite 
sufficient to characterize the aggregate ; but it must be added that the sides of the 
thorax have a very fine margin, the prosternal process is never very elongate and 
the intercoxal process of the metasternum has its anterior part reflexed and im- 
pressed in adaptation to the apex of the prosternal process, but does not possess 
any prolonged groove, or highly developed depression in front. The hind cox 
are always large, and the wing of the metasternum terminates as a slender band 
deflexed outside of the front border of the hind coxa. The swimming legs are 
slender, more especially the tibiae and tarsi, for even in the species where the femora 
are distinctly incrassate, the tibize and tarsi are scarcely correspondingly developed. 
The coxal lobes always display a well marked coxal incision and the apex of the 
posterior femur is destitute of accumulated sete. The hind tarsi are almost, or 
quite, destitute of lobing of the joints externally, and are terminated by two small, 
equal, claws. The male tarsi are sometimes scarcely different from those of the 
female (Colymbetes parvulus, Boisd.), in other cases the three basal joints become 
considerably dilated, and furnished beneath with four rows of distinct palettes, 
placed almost immediately on the tarsus ; their claws are not subject to much 
elongation or development. The females often show a highly developed sexual 
sculpture, which seems to be either variable or polymorphic within the limits of 
one species: this sexual sculpture is independent of the peculiar sculpture already 
alluded to, which however is also to some extent liable to sexual differences. 
The genus is wanting in cold climates, but is widely distributed in the warmer 
parts of the world, and will probably prove to be one of the most extensive in the 
Dytiscide. A large proportion of the one hundred species known to me are at 
present very rare in collections, and it has for this reason been impossible for me 
