948 On Aquatic Carnivorous Coleoptera or DytiscidcB. 



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 coxse ; 

 the anterior border of this part attains its greatest forward extension umch nearer 

 to the middle (longitudinally) of the body than it does in auy other Dytiscidae, and 

 thus a peculiar shape is given to the wings of the metasternum ; and the interior 

 lamina of the coxae is very separated for its whole length from the external 

 lamina, and projects and foims an axilla, into which tlie interior Ijorder of the 

 hind femur is I'eceived when it is flexed. This structure of the hind coxae, under 

 various modifications, is found in all Noterides, and is not found in any other of 

 the Dytiscidaj, 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 ejjisternum 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 

 Dytiscidae not included in the tribe. 



The hind coxae var}' very much in their area as in other Dytiscidae, but whereas 

 in other Dytiscidae when they increase their area and encroach on the metasternum 

 the anterior border attains its greatest ajDproach to tlie front of the body more or 

 less near the epipleurae, in Noterides, as already stated, this greatest apjiroach is 

 made much nearer to the middle line of the body, and so at a 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 geims to be really an exception to the other species in any other respect besides 

 that of the obliteration of 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 

 Noteridae 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. 

 I'ulobius 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 Dytiscidae, such as Agabinus and Hyderodes, very 

 widely separated genera belonging respectively to Agabini and D3'tiscini. 



The small size of the mesothoracic eiiimeron — one of the features characteristic 



