On Aquatic Carnivorous Coleoptera or Dytiscide. 243 
Agabus however it usually extends to the apex. In Hyphydrus the elytral ridge 
shows a very peculiar structure; a little in front of the extremity there is an 
elongate prominent tongue, which projects towards the edge of the wing-case and 
even a little beyond it, leaving a small space between it and the inner face of the 
wing-case, and into the deep groove so formed fits the upper portion of the ventral 
plate ; as the result of this the two wing-cases at the extremity are so firmly locked 
together, that they can only be separated by first lifting them up from the body 
till the extremity of the ligula is free: a similar but smaller ligula is seen in 
Coelambus, and in some other genera of Hydroporini it is found in a still less 
perfected state. In Queda and Pachydrus the elytral ridge attains its greatest 
development ; it is elongate, and for nearly its whole length forms with the face of 
the elytron a kind of groove into which are received the edges of the vertical 
segments ; near its extremity 1t becomes more prominent and thickened, and waved 
in such a manner as almost to form a broad double ligula, the elytra are thus locked 
together in an extremely firm manner. In Pelobius there exists two structures of 
an unique character on the inner face of the wing-case ; one is a raised longitudinal 
band at the extremity near the suture, on each elytron; these bands are marked 
with transverse striz, and are a part of an apparatus for producing sound. The 
second is a large protuberance near the outer margin, just in front of the middle; 
this protuberance forms a cavity into which is received a horny process on the upper 
edge of the basal ventral segment, and like the ligula in Hyphydrus serves the 
purpose of very firmly locking together the two wing-cases. 
Wines.—Wings are always present in the Dytiscidee, and are well developed 
Ay A 
and large, except in a very few species (Colymbetes bifarius No. 757 e. g.) where 
they are rudimentary. They are folded in a complex manner, and placed in close 
adaptation to the inner surface of the wing-cases, not touching the body, and thus 
when the elytra are more than usually diaphanous (as in many Laccophili) the 
veins of the wings may be slightly visible through the wing-cases, giving the latter 
the appearance of being marked or coloured in an unusual manner. There are 
two different folds to adapt them to the size of the wing-cases ; one of these is 
a simple lapping over of the basal portion, but the other is a very complicated 
longitudinal and transverse fold and is situated on the front part of the wing just 
beyond the middle, and is exactly similar to the corresponding fold of the wing 
in the Carabide and Cicindelide. The costal and subcostal nervures are close 
together, and form the front border of the wing, the former of them is continued 
to the apex of the wing, and it is by traction on this costal nervure that the wing 
is unfolded, as may be readily ascertained by cutting off the wing of a freshly 
killed specimen, and then pulling the base of this nervure with a pair of forceps; 
the subcostal nervure on the other hand is continued only as far as the transverse 
fold (or carpa) of the wing, when it is turned backwards, so as to leave an irregular 
cell or stigma immediately behind the costa; this subcostal nervure is, when 
TRANS. ROY. DUB. SOC., N.S., VOL. II. BS 
