920 On Aquatic Carnivorous Coleoplera or Dijtiscidce. 



II. 2. — Gioup SuPHisixi. (FiJe p. 2G7.) 



Only two genera, one consisting of three species, tlie other an autogenus, forni 

 this secondary aggregate : 



The form of the individuals is short, and excessively convex above ; the pro- 

 sternum in front of the coxte is very reduced and small, so that the coxse are very 

 near its front edge, and along the middle longitudinally the prosternum is a good 

 deal thickened ; the prosternal process is nearly truncate behind ; although the 

 metasternum is very short the suture between it and the hind coxa does not approach 

 very near to the middle coxa. The swimming legs are very feeble, and their articula- 

 tions are a good deal separated from one another ; the hind femora have elongate 

 projecting setae ; the front legs are wonderfully modified, in the manner detailed in 

 the description of Colpius (p. 837). 



The structure of the prosternum, and the extreme differentiation of the fi'ont legs 

 authorize tlie treating of these few species as a distinct aggregate : it is somewhat 

 approached by Synchortus of the Noterini, for in this there is a slight approximation 

 to the prosternal structure of the Suphisini, but in Synchortus the hind legs are with- 

 out femoral cilite at the extremity of the hind margin. It has perhaps really more 

 claims to relationship with Hydrocanthini, where as in the Suphisini the femoral ciliae 

 are present, but the Hydrocanthini seem to me to present such an important depar- 

 ture from the Suphisini in the prosternal structure, that I have thought it would be 

 unnatural to class them together in the same secondary aggregate. 



These insects are of interest inasmuch as that they are amongst the lowest 

 Dytiscidse if the hind legs and coxae are the points considered, and yet they display 

 in the most extreme degree of perfection the structure of the tibiaj characteristic 

 of the higher Noterini ; in other words the hind legs, coxse, and general form class 

 them as amongst the least differentiated of the water beetles, while the stnicture of 

 the front legs class them as amongst the most extremely differentiated. It is thus 

 impossible to look upon them as displaying any genetic relationship with the 

 nearest allies ; they are below them (or ancestral) in one important respect, above 

 them (or more recent) in another important respect. Of the two forms included 

 in the Suphisini — Colpius and Suphis — Colpius is probably to be looked on as the 

 lower form, and from its retention of primitive characteis is certainly one of the 

 most interestinsf water beetles. 



The Suphisini are peculiar to the New World, Colpius has been found only in 

 the United States, Suphis only in South America and the west Indies. 



II. 3. — Group Hydrocanthini. {Vide. p. 268.) 



Only two genera, one comprising forty-one, the other twelve, species, constitute 

 this secondary aggregate. The individuals vary in size, from 2 to 8 m.m. of length, 

 the form is very convex (especially transversely) above, flat beneath, the outline 



