936 On Aquatic Carnivorous Coleoptera or Uytiscidce. 



as the outer one, but this character although it has been considered the essential 

 distinction of Colymbetes (auct.) is not trustworthy, for in Colymbetes pacificus (No. 

 920) we have a species where the claws are almost positivel}' equal. 



The sculpture of the upper surface in the genus Colymbetes must not be passed 

 over without remark, for it is almost without parallel in the Coleoptera ; this 

 peculiar sculpture consists of elongate transverse striae on the wing-cases, giving 

 rise to a file-like appearance ; it is to some extent sexual, and attains its maximum 

 of development in the female of Dytiscus dolabratus (No. 971). It is all the more 

 worthy of remark because the tendency of development in the water beetles is 

 towards the attainment of a smooth and polished surface. lu the other genera of 

 Colymbetini no trace of this transverse sculpture exists, but in Scutopterus a 

 beautiful reticulation of fine but rather deep lines covers the upper surface, and in 

 Meladema coriacea, a most peculiar scale-like sculpture exists. In Ehantus the 

 surface is usually very polished and smooth, but in most species a very delicate 

 excessively fine, minute reticulation is detected, with a good glass, on the wing- 

 cases ; in the little developed Col. pacificus however the reticulation on the wing- 

 cases does not exist, but is replaced by an obscure punctuation, while on the other 

 hand in that highly developed species of Rhantus, Dytiscus pustulatus, the fine 

 reticulation is very distinct, and like what exists in Ilybius. 



The Colymbetini as a whole are approximated by Ilybius of the Agabini, that 

 aggregate displaying enlargement of penultimate stigma, lobing of the hind tarsi, 

 and conspicuous inequality of their claws, characters which are all of them still 

 more pronounced in Colymbetini. Scutopterus in Colymbetini approaches Agabini 

 by the broad ventral side pieces, by the little lobing of the hind tarsi, and its 

 sculpture which is a great development of Agabus sculpture. Although one 

 aggregate of the Colymbetini thus approximates to Agabini, and one member of 

 the Agabini approximates to Colymbetini, yet there is no approximation between 

 these two aggregates themselves ; Colymbetini sends out as it were a pseudopod in 

 the direction of Agabini, and Agabini a pseudopod in the direction of Colymbetini, 

 but the two pseudopods so protruded are not in directions which lead one to 

 .suppose they have had, or will have, any actual contact. 



Another approximation is made in certain respects to Colymbetini by Lancetes ; 

 ttie species of that genus have in fact hitherto been universally placed by writers 

 on the subject actually as part of the genus Colymbetes, and they approach the 

 Colymbetini by their general appearance, by the comparatively blunt apex of the 

 metathoracic episternum, by the comparatively large side wings of the metasternum 

 and by the very unequal hind claws ; on the other hand by the truncate elytra, 

 as well as by the little lobed hind tarsi, Lancetes tends rather towards Agabini 

 than towards Colymbetini : and it is of course positively excluded from the latter 

 group by the absence of stigmatic rugse. 



The mention of this latter character reminds us of another approximation 



