920 On. Aquatic Carnivorous Coleoptera or Dytiscide. 
II. 2.—Guioup Suruism1. (Vide p. 267.) 
Only two genera, one consisting of three species, the other an autogenus, form 
this secondary aggregate : 
The form of the individuals is short, and excessively convex above; the pro- 
sternum in front of the cox:e is very reduced and small, so that the coxze 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 sete ; 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 front legs 
authorize the 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 cilize at the extremity of the hind margin. It has perhaps really more 
claims to relationship with Hydrocanthini, where as in the Suphisini the femoral cilize 
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 
Dytiscide if the hind legs and cox are the points considered, and yet they display 
in the most extreme degree of perfection the structure of the tibize characteristic 
of the higher Noterini; im other words the hind legs, coxse, and general form class 
them as amongst the least differentiated of the water beetles, while the structure 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 characters is certainly one of the 
most interesting 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. 
Il. 3.—Group Hyprocanruini. (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 
