On Aquatic Carnivorous Coleoptera or Dytiscidce. 943 



is very distinctly left exposed by the epipleura, while in other cases it cannot be 

 at all perceived when the wing-cases are in the natural closed condition. The 

 epipleuree show much variation in their width from species to species. The 

 hind coxEe are always very largely developed, and their upper border of the form 

 already described, The coxal processes never have a large extension either in the 

 longitudinal or transverse direction ; the coxal lines are but little turned outwards 

 near their termination, and they extend but a short distance in the anterior direction, 

 so that they remain extremely remote from reaching the front border of the coxa, 

 their extension forwards is however indicated by a curved series of punctures in 

 front of the termination of the actual line. In the Australian genus Homceodytes 

 the coxal lines are absent, and the coxal processes of rather unusual form. 



It is in this group of the Dytiscidfe that the swimming legs attain their greatest 

 and most admirable development ; the femora are very broad, and the tibiae are 

 often so thick and short that their length does not greatly exceed their breadth : 

 in Dytiscus roeselii actual measurement shows about 3| m.m. of length, by 2g m.m. 

 of breadth. The superior of the two apical spurs is ot slender form, and is 

 more or less profoundly canaliculate along its inner face, and is either simply 

 acuminate at the apex, or largely furcate there, or minutely tricuspidate ; the 

 inferior spur is dilated and flattened, but is quite acute at the apex, and is longer 

 than, as well as broader than, the other. The tarsi are very thick and their hind 

 margins though sinuate are not distinctly lo bate-produced at their outer edges, 

 and are destitute of fine ciliaB. Tlie claws are very vai'iable ; either there exists 

 only a single thick, pointed, straight and immobile claw, or there are two, more 

 slender, straight, equal claws, or the two claws may be unequal to a greater or 

 less degree in length or thickness. It has been supposed that when there is only 

 one claw present, it is because the two claws have become soldered and amalgamated 

 into a single one ; and as a groove may be detected running along the length of 

 the claw this is cited as a relic of the original distinction into two claws : this is 

 however quite erroneous. When there is only one claw present it is because the second 

 claw is undeveloped or rudimentary ; this second claw in point of fact is present in 

 all degrees of development ; and moreover where there are two well marked claws 

 present in the genus, each of the two claws may be seen to be deeply channelled 

 {vide Cybister giganteus, No. 1,11 V) showing conclusively that the channel is not 

 evidence of two claws being amalgamated. 



The Cybistrini are found in most parts of the world, except that they do not 

 extend into the cooler regions, and must be considered as characteristic of the 

 warmer and warm-temperate regions. The Australian species are much more 

 aberrant than those found in any other part of the world. 



