On Aquatic Carnivorons Coleoptera or Dytiscidce. 947 



Hydrocanthus where it can be brought much nearer to the middle line of the body. 

 In Suphis difFormis, however, as in the higher Noterides, the front border of the 

 coxa attains its greatest anterior extension near the middle of the body and thus 

 forms a striking contrast to the Hydroporides, where the greatest anterior extension 

 of the coxa is near the outside ; in this respect the approximation of the more 

 primitive forms of Noterides to Pelobius is very decided, and in fact, so far as the 

 shape of the metasternum and hind coxae go, there is no great difference between 

 Pelobius and Suphisini. 



The hind coxae are in the Noterides modified in a very peculiar manner ; the 

 coxal processes are enormously developed and are projected on to a different plane 

 from the external lamina of the coxse, so as to form a prominent platform ; a concavity 

 or elongate axilla is formed by the inner portion of the outer lamina being pushed 

 in above this prominent platform, and this axilla extends the whole length of the 

 coxa, and as the middle of the metasternum is more or less prominent in a similar 

 manner to the coxal processes, a kind of prominent platform continuous with the 

 prosternum is formed, extending the whole length of the breast. This platform is 

 extremely conspicuous and remarkable where the swimming legs are highly 

 developed (especially in Hydrocanthus), but scarcely exists in Suphis, for although 

 in it the elongate axilla formed by the coxal processes exists, there is not the least 

 prominence of the middle of the metasternum. The coxal processes show no trace 

 of the existence of any coxal lines or coxal borders, and their posterior outer angle 

 is acute or rectangular ; the coxal cavities are either distinctly separated or 

 absolutely contiguous : Hydrocoptus is the only genus in which the coxal lines can 

 be detected, they extend the whole length of the coxa and mark off a fine coxal 

 border. 



The swimming legs vary greatly in their development ; the most characteristic 

 peculiarity is that in the higher forms the tarsi do not share in the incrassation of the 

 femora 'and tibiae to the same extent as in other Dytiscidae, thus in Hydi'ocanthus, 

 the tarsus is not half so broad as the tibia ; the tibia moreover never becomes 

 shorter than the femur ; and it seems, therefore, that it plays to a large extent the 

 part performed by the tarsus in other Dytiscidae; the spurs of the tibiae are never 

 greatly incrassate, but one of them is occasionally beautifully serrate along its 

 inner face (Hydrocanthus laevigatus). 



The tarsi have the basal joint always very elongate in proportion to the others ; 

 and the claws appear to be always small and insignificant, and so far as known are 

 both always present, and nearly equal. 



Ciliae at the hind angle of the posterior femur are either present or not ; in 

 Hydrocanthus they attain a greater development than in any other Dytiscida3. 



Both the front and middle tarsi in the Noterides are distinctly 5-jointed, and 

 there is no bilobing of the third joint ; when the male front tarsi are thickened, 

 the incrassation is chiefly confined to the basal joint, and there is not the least 



TRANS. ROT. DIB. SOC , N.S. VOL. II. 6 F 



