On Aquatic Carnivorous Coleoptera or Dytiscide. 235 
fitted together, and more or less strongly soldered together on the middle line of 
the body by a straight longitudinal suture ; a suture or impressed line runs near 
the outer border of the internal lamina, and proceeding forward, either reaches the 
anterior border of the coxa (as in most Agabi), or becomes obsolete in front; in this 
latter case no real line of demarcation exists between the external and internal 
laminze in front of the part where this line stops short; this line I call the coxal 
line, or speaking of the two together, coxal lines. The hinder part of the internal 
lamina is prominent, and presents a free edge over which the trochanter of the 
swimming leg plays, and which by its shape determines to some extent the kind of 
motion made by the swimming leg; this is the coxal process, or coxal lobe. This 
process or lobe usually has, at any rate towards its termination, a kind of external 
margin or border, marked off by the terminal portion of the coxal line ; this is the 
coxal border. The hinder edge of the coxal process is very frequently marked by 
a short closed suture (see Dytiscus) or a small notch or emargination ; this I have 
called the coxal notch. The external division or lamina of the hind coxa is always 
larger than the other, sometimes enormously larger ; its front border proceeding 
from the middle is directed outwards and at the same time more or less forwards, 
but before reaching the side, turns more or less abruptly backwards, so as to form 
a sort of curve or arch of very diverse forms; it is soldered to the metasternum, 
but it passes outwards beyond this latter behind the posterior point of the epister- 
num, thus reaching the margin of the epipleura; it does not, however, there 
terminate but (as is seen on taking off the wing-case) is reflexed upwards passing 
behind the epimeron and terminating externally, in an either angulated or rounded 
form, by articulation with the outside of the post-scutellum, by the intervention of 
a small piece considered by Schioedte (Dan. El. p. 377) to be a trochantin. The 
hind margin of the exterior lamina (as seen where the specimen is entire) is likewise 
directed somewhat towards the front, and near the epipleura forms a considerable 
curve or sweep, which is continued under the wing-case, to the outside extremity 
of the coxa ; this apparent hind margin is not however the real hind margin, for on 
dissection it is seen that the coxa is to a large extent reflected in a very round curve 
upwards to the interior of the insect; this reflected and concealed portion of the 
coxa may be called its abdominal portion, and in Hyphydrus is very distinctly 
marked off along the whole breadth of the coxa by a raised line or margin. The 
exterior lamina of the coxa differs greatly in size and shape, and its variations offer 
one of the best modes of distinguishing the genera and species. The changes of 
form occur on its anterior portion. Thus in Pelobius and Amphizoa where the 
Dytiscid coxa is seen in its most rudimentary condition, the metasterno-coxal suture 
proceeds directly outwards, without stretching forwards at all, so that the two 
sutures together form a nearly straight line extending all across the under surface : 
we find the other extreme in the genus Eretes, where the metasterno-coxal 
suture proceeds almost directly forwards, thus the sutures of the two sides at their 
TRANS. ROY. DUB. SOC., N.S. VOL. II, 21 
