On Aquatic Carnivorous Coleoptera or Dytiscide. 949 
ot the Noterides—appears to be true of all the species of the tribe, but it is 
likewise found insome Bidessini, in Sternopriscus, and even (though not so remarkably) 
in Pelobius; now as all these widely different forms have in common the fact that 
the mesosternun is placed on a plane more continuous with the plane of the meta- 
sternum than it is in other Dytiscidee, it is clear that the small size of the meso- 
thoracic epimeron is correlative with the less amount of change of position of the 
mesosternum, or in other words, just so much as the mesosternum has been bent 
towards the metasternum, just so much has the epimeron increased in size: 
although Bidessus and Sternopriscus resemble Noterides in the small size of the 
epimeron, they do net agree with it in its comparative obliteration at its upper or 
episternal angle; this is clearly because growth of the mesothoracic episternum 
has gone on in Noterides (owing to greater use of the middle legs in locomotion), 
while no such growth has taken place in Bidessus and Sternopriscus. ‘hus we see 
that the form of the mesothoracic epimeron in the Noterides is the result of the little 
change of plane of the mesosternum plus the unusual growth of the episternum ; 
and we can clearly see that these peculiarities are properly considered as amounting 
to evolution from more primitive to higher forms, and we see further that the 
likeness presented by other water beetles in this respect is not due to any genetic 
connection or common ancestry, but rather should be looked on as community 
of structure owing to similarities of evolution. 
Another peculiarity of the Noterides, viz., the relation between the prosternal 
process and metasternum, need not occupy us long; it is very striking in Hydro- 
eanthini, but much less so in the other groups, and all that need be said is that 
whereas in Hydroporides and some other groups accurate adaptation of these 
parts has been gained comparatively late in the process of evolution, on the other 
hand, in the Noterides it has been a striking feature even in some of the early 
forms. Sternopriscus, which has been just alluded to as approximating to Noterides 
by one part of the structure, is in this respect abruptly different, it bemg one of 
the forms where co-adaptation between the prosterna! process and metasternum is 
most incomplete. 
The unusual development of the spur at the apex of the front tibia, is not present 
in all the forms, it seems to be absolutely deficient (so far as I can see) in Hydro- 
coptus and Notomicrus, but it is present in all the higher forms, and in some of the 
lower ones, and attains its greatest evolution in Suphisini, which in some other 
respects are to be considered low or primitive forms. 
Although, so far as we know of them at present, and probably really at the present 
epoch, the Noterides form a very fragmentary tribe, yet it is one which is very well 
adapted for studying in connection with eyolution; and I have come to the 
conclusion that certainly there is no ancestral relation between the different 
forms comprised in it; after careful consideration I feel sure that no species, 
of it can be considered the ancestor of any other species, no genus the ancestor of 
6F2 
