On Aquatic Carnivorous Coleoptera or Dytiscidce. 937 



made towards the Colymbetini — viz., by the DytiscinI ; for these are the only 

 DytiscidaB except the Colymbetini that possess the stigmatic rugae : 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 siJecies 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 

 jieculiar species, but the Canary Islands have only a species found in Southern 

 Europe, which is absent from Madea'a. Some species of Colymbetes are peculiar 

 or nearly so to the arctic regions ; and in the New World besides the numei'ous 

 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 

 calidus, Fab.) 



II. 12.— Group Dytiscini. {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 



