936 On Aquatic Carnivorous Coleoptera or Dytiscide. 
as the outer one, but this character although it has been considered the essential 
distinction of Colymbetes (awct.) is not trustworthy, for in Colymbetes pacificus (No. 
920) we have a species where the claws are almost positively 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 striz 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. In 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 seulpture exists. In Rhantus 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 
ageregate 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 
agoregate 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 ; 
the 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 ruge. | 
The mention of this latter character reminds us of another approximation 
