On Aquatic Carnivorous Coleoptera or Dytiscide. 191 
‘cases are so acuminate as to be spinose (Celina, Methles, some Hydrovati) ; this 
occurs only in species whose individuals are of small size, and in all such cases the 
swimming legs are very feeble. The most remarkable peculiarity in the outline is — 
its continuity, or freedom from interruption at the junction of the base of the 
prothorax with the wing-cases: this continuity is frequently so perfect that no 
break in the regularity of the form can be detected at the spot indicated ; this 1s the 
case with all the higher forms, and the best swimmers. But there are in the family 
some exceptions in which there is a great break in the outline at this spot, the 
base of the thorax being much narrower than the base of the elytra (Vatellini, 
Tyndallhydrus, Andex, Anisomera) ; this discontinuity is always associated with a 
peculiarity in the sternal pieces ; in its extreme cases sach as in the Vatellini, Andex, 
and Tyndallhydrus, the prosternal process does not reach the mesosternal process, 
while in those cases where the discontinuity is less marked, it will be found that 
although the prosternal process may attain the metasternum, the mesosternum is less 
completely vertical in its direction than usual; this will be found to be the case in 
Agabus cephalotes and in Dytiscus dorsalis (No. 630, Hydroporus). In the genus 
Deronectes it frequently happens that there is a considerable difference between the 
sexes of one species in respect of the continuity of the outline of the thorax and 
wing-cases and it is always in the female sex that the continuity is the more broken. 
(See gen. Deronectes, No. 454 Hydroporus lareynei, No. 455 Hydroporus opatrinus, 
No. 472 Dytiscus depressus, &c.) 
The group Noterides presents a constant difference in outline from the other 
Dytiscidez inasmuch as the greatest width is in front of the middle of the body 
instead of behind it, and the species of this group have consequently the posterior 
portion of the body narrower than the other Dytiscide, so that in them this part 
is less broad than the anterior half, while, as we have just seen, in most other 
species of the family the reverse is the case. As regards the convexity of the body 
the Dytiscidz show a great deal of variation, they are either subdepressed or little 
convex, or they may be very convex; the flattest or most depressed forms are found 
in the tribes Colymbetides and Hydaticides, especially in the genera Copelatus, 
Lacconectus, Platynectes, and (a few) Agabus, while the most convex species are all 
small insects, of short form, such as Colpius and Suphis among the Noterides, most 
of the species of the groups Hydrovatini and Hyphidrini, and many of the group 
Bidessini; in the Hydroporini some of the genera consist of convex forms, as 1n 
Hyphoporus, Herophydrus, Coelambus and Chostonectes; while Deronectes and 
Hydroporus comprise forms which as a rule are much more depressed. The larger 
and more powerful forms are usually of moderate convexity. When the convexity 
is very great it is as a rule confined chiefly to the under surface ; this is shown ina 
very marked manner by Pachydrus and Hyphydrus; in the convex Hydrovatini 
the convexity is obtained by about equal curvature of both the upper and lower 
surfaces; the Noterides display another peculiarity in this respect inasmuch as being 
