On Aquatic Carnivorous Coleojytera or Dytiscidie. 235 



fitted together, and more or less strongly soldered together on the middle line of 

 tlie 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 

 laminre 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, 

 l)ut 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. Tlrus 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 



TBAItS. BOY. DUB. SOC, N.S, VOL, n. SI 



