948 On Aquatic Carnivorous Coleoptera or Dytiscida. 
tendency for the three basal joints to be co-adapted and dilated to form a 
saucer ; the clothing of the under surface is never more, or other than, a few small 
palettes. 
The Noterides are characterized specially by the structure of the hind coxz ; 
the anterior border of this part attains its greatest forward extension much nearer 
to the middle (longitudinally) of the body than it does in any other Dytiscidze, and 
thus a peculiar shape is given to the wings of the metasternum ; and the interior 
lamina of the coxe is very separated for its whole length from the external 
lamina, and projects and forms an axilla, into which the interior border of the 
hind femur is received when it is flexed. This structure of the hind coxe, under 
various modifications, is found in all Noterides, and is not found in any other of 
the Dytiscidee, except the totally distinct Pelobius (in which, inter alia, the scutellum 
is visible), There are some other characters by which most of Noterides may be 
recognized, but they are not quite so constant or peculiar as the coxal structure. 
These are: first, the small size of the mesothoracic epimeron in comparison with 
the episternum and its sublinear form; second, the accurate adaptation of the 
prosternal process to the inter-coxal process of the metasternum; and third, the 
unusual development of one of the spurs of the front tibia to form a hook. I 
now proceed to discuss briefly the amount of variation of these characters within 
the limits of the tribe itself, and to what extent they are possessed by other 
Dytiscidee not included in the tribe. 
The hind coxee vary very much in their area as in other Dytiscide, but whereas 
in other Dytiscidee when they increase their area and encroach on the metasternum 
the anterior border attains its greatest approach to the front of the body more or 
less near the epipleuree, in Noterides, as already stated, this greatest approach is 
made much nearer to the middle line of the body, and so ata greater distance 
from the epipleura ; this character so far as can be seen is absolutely constant, but 
it cannot be tested in the minute Notomicri, for in these the outline of the coxa 
cannot be distinguished from the metasternum; but there is no reason for supposing 
the genus to be really an exception to the other species in any other respect besides 
that of the obliteration ot the suture: Pelobius is the only Dytiscid outside of 
the Noterides in which the coxa has at all the Noterid form; and although 
nothing can look more dissimilar than the coxa of Pelobius and one of the higher 
Noteridze such as Hydrocanthus, yet if we compare it with one of the lower 
Noterides, such as Suphis or Colpius, the likeness of the two is readily perceived. 
Pelobius has moreover the internal lamina of the coxa abruptly distinguished 
from the outer lamina for its whole length longitudinally, and thus again 
resembles the Noterides ; this latter peculiarity of the structure of the coxa occurs 
however in other genera of Dytiscidz, such as Agabinus and Hyderodes, very 
widely separated genera belonging respectively to Agabini and Dytiscini. 
The small size of the mesothoracic epimeron—one of the features characteristic 
