On Aquatic Carnivorous Coleoptera or Djtiscidce. 191 



-cases are so acuminate as to be spiiiose (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 

 prnthorax 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 is 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 such as in the Vatellini, Andex, 

 and Tyndallhydrus, the prosternnl 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 ma}' attain the metasternum, the mesosternura 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 

 Dytiscidae 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 Dytiscidse, 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 Dytiscidae 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 Colyuibetides 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 in 

 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 in a 

 very marked manner by Pach3^drus 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 



