On Aquatic Carnivorous Coleoptera or Dytiscide, 947 
Hydrocanthus where it can be brought much nearer to the middle line of the body. 
In Suphis difformis, however, as in the higher Noterides, the front border of the 
coxa attains its greatest anterior extension near the middle of the body and thus 
forms a striking contrast to the Hydroporides, where the greatest anterior exteusion 
of the coxa is near the outside; in this respect the approximation of the more 
primitive forms of Noterides to Pelcbius is very decided, and in fact, so far as the 
shape of the metasternum and hind cox ge, there is no great difference between 
Pelobius and Suphisini. 
The hind coxze are in the Noterides modified in a very peculiar manner; the 
coxal processes are enormously developed and are projected on to a different plane 
from the external lamina of the coxze, so as to form a prominent platform ; a concavity 
or elongate axilla is formed by the inner portion of the outer lamina being pushed 
in above this prominent platform, and this axilla extends the whole length of the 
coxa, and as the middle of the metasternum is more or less prominent in a similar 
manner to the coxal processes, a kind of prominent platform continuous with the 
prosternum is formed, extending the whole length of the breast. This platform is 
extremely conspicuous and remarkable where the swimming legs are highly 
developed (especially in Hydrocanthus), but scarcely exists in Suphis, for although 
in it the elongate axilla formed by the coxal processes exists, there is not the least 
prominence of the middle of the metasternum. The coxal processes show no trace 
of the existence of any coxal lines or coxal borders, and their posterior outer angle 
is acute or rectangular; the coxal cavities are either distinctly separated or 
absolutely contiguous: Hydrocoptus is the only genus in which the coxal lines can 
be detected, they extend the whole length of the coxa and mark off a fine coxal 
border. 
The swimming legs vary greatly in their development ; the most characteristic 
peculiarity is that in the higher forms the tarsi do not share in the incrassation of the 
femora ‘and tibizs to the same extent as in other Dytiscide, thus in Hydrocanthus, 
the tarsus is not half so broad as the tibia; the tibia mvureover never becomes 
shorter than the femur; and it seems, therefore, that it plays to a large extent the 
part performed by the tarsus in other Dytiscidze; the spurs of the tibiae are never 
greatly incrassate, but one of them is occasionally beautifully serrate along its 
inner face (Hydrocanthus leevigatus). 
The tarsi have the basal joint always very elongate in proportion to the others ; 
and the claws appear to be always small and insignificant, and so far as known are 
both always present, and nearly equal. 
Ciliz at the hind angle of the posterior femur are either present or not; in 
Hydrocanthus they attain a greater development than in any other Dytiscide. 
Both the front and middle tarsi in the Noterides are distinctly 5-jointed, and 
there is no bilobing of the third joint; when the male front tarsi are thickened, 
the incrassation is chiefly confined to the basal joint, and there is not the least 
TRANS. ROY. DUB. SOC., N.S. VOL. II. 6 F 
