On Aquatic Carnwvorous Coleoptera or Dytiscida, 937 
made towards the Colymbetini—viz., by the Dytiscini; for these are the only 
Dytiscidze except the Colymbetini that possess the stigmatic rugze: and this 
approximation is rendered more distinct by the fact that the Dytiscini show us 
perfected that wonderful development of the terminal stigmata of which the 
Colymbetini show the rudimentary stages; but in this case again we must look 
upon the approximation as pseudopods, so to speak, not as indications of any past, 
present, or future amalgamation of the two aggregates, for in many others of the 
most constant characters of the Dytiscini there is no tendency towards contact, 
but quite the contrary. Thus Colymbetini are characterized by little extension of 
the coxal processes in the longitudinal direction, Dytiscini by a most remarkable 
extension of the processes in the longitudinal direction; Colymbetini have highly 
displayed lobing of the hind tarsi, which is nearly absent in Dytiscini ; Colymbetini 
have remarkably constantly very unequal hind claws, which is absolutely absent in 
Dytiscini; so again we should find it with numerous other characters; and more- 
over there is no tendency whatever for any one member of the Dytiscini to make any 
approach to any one member of Colymbetini. 
The conclusion to be derived from a careful consideration of the approximations 
between Colymbetini and other allies does not therefore in the least tend to raise 
or to confirm the idea of descent from a common ancestor; the more thoroughly 
the details are mastered, the more does the realization of such an idea become hazy 
and elude the mental grasp. 
The species inhabit specially the cool and temperate regions of the Old World, 
from whence a few have spread into adjacent regions. So far as known to me they 
are wanting in Australia, except that a species found almost everywhere in the 
Eastern Hemisphere occurs there; as however two or three aberrant species occur 
in the Pacific Islands, such may also be found in Australia, A single very peculiar 
species is reputed from New Zealand, where also the same widely distributed 
Rhantus that is found in Australia occurs. Two or three aberrant species are 
known from Southern Africa and Madagascar: Madeira shows one or two very 
peculiar species, but the Canary Islands have only a species found in Southern 
Europe, which is absent from Madeira. Some species of Colymbetes are peculiar 
or nearly so to the arctic regions; and in the New World besides the numerous 
species found in North America some others are found in or near the Andes, and 
one species of Rhantus is abundant in the warm parts of the New World (Dytiscus 
ealidus, Fab.) 
Il. 12.—Group Dyrisciui. (Vide p. 632.) 
This secondary aggregate is formed by twenty-five species arranged in two genera. 
The size of the individual in all the species is large, not less than half an inch of 
length, and may attain one and a half inches. The swimming legs are rather 
slender and are terminated by two nearly equal curved claws ; the posterior margins 
