898 On Aquatic Carnivorous Coleoptera or DytiscidoB. 



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 

 distinoaiished 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. unguiculai-is,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 ot 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 dii-ection, show an evident emargination at their sl'ghtly 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 w^hich 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 SCUTOFTERUS. {Vide p. G06.) 



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, e.y.). 

 From all the other aggregates forming the Colymbetini (/.c, those first aggregates 

 that have stigmatic rugse) the genus is abundantly distinguished by the broad 

 ventral side pieces which are formed as in Agabus. In Meladema the length <>f 

 the fourth ventral side piece is about six times its breadth, while in Scutopterus 



