898 On Aquatic Carnivorous Coleoptera or Dytiscide, 
it is easily seen that this middle gap is partly filled up by a growth of the exces- 
sively fine margin that in the allied groups borders the inner edge of the coxal pro- 
cesses ; thus along the inner and upper part of this middle separation of the coxal pro- 
cesses there is seen in Colymbetes lanceolatus a sort of broad border marked oft by a 
deep suture ; in Colymbetes nigriceps, the evolution has been carried to a greater 
extent, and the suture in question is obliterated although its position is still to be 
distinguished by some remaining punctures, and thus the form of the coxal processes 
in that species approaches very much nearer to Rhantus. The apices of the elytra are 
much truncate, but in a variable degree; in L. unguicularis, this truncation is extreme. 
The hind legs are rather elongate and slender, their femora are but little incrassate, 
and have a series of setigerous punctures placed along the middle of their under 
surface, somewhat near their outer extremity ; their tarsi have the hind margins 
of the joints externally slightly lobed beneath, and are terminated by two claws, 
very variable according to species. 
These are interesting insects and will probably ultimately be distributed in three 
different genera, viz., 1, Col. lanceolatus; 2, L. unguicularis, and the two species 
following it; and 3, Rhantus marginatus. In Col. lanceolatus the elongate palpi 
when viewed in one direction, show an evident emargination at their slightly truncate 
extremity, and this is also seen in Rhantus marginatus, where the palpi are much 
shorter. In Col. lanceolatus the prosternal process, as is shown by its margin, is 
but little compressed at the sides, while in the others it is very strongly compressed. 
The series of setigerous punctures distributed along the hind femur may be 
considered I think homologous with those which in the Agabus allies are accumu- 
lated together at the hind angle of the femur. The approximation of Rhantus 
marginatus, (No. 917) to Coptotomus is quite clear and has been alluded to in the 
notes on that genus; it is also evident that Colymbetes nigriceps makes a real 
approach to the genus Rhantus, though remaining very distinct therefrom. 
The species are Chilian, but one is found at Buenos Ayres, and another in 
Australia and New Zealand. 
I. 61.—Genus SOUTOPTERUS. (Vide p. 606.) 
Two species form this aggregate. These insects are of different appearance to 
the other Colymbetini, and remind one somewhat of large Agabi. Leconte indeed 
described the only species known to him as an Agabus not a Colymbetes, and they 
have a sculpture of the upper surface consisting of a very highly developed fine 
reticulation, not very different to what exists in Agabus, (A. tristis, No. 74, eg.). 
From all the other aggregates forming the Colymbetini (i.c., those first aggregates 
that have stigmatic rugz) the genus is abundantly distinguished by the broad 
ventral side pieces which are formed asin Agabus. In Meladema the length of 
the fourth ventral side piece is about six times its breadth, while in Scutopterus 
