On Aquatic Carnivorous Coleoptera or Dytiscide. 195 
selves are lost amongst the general punctuation of the surface: in some cases 
(Colpius inflatus e.g.) I fail however to find any trace of their existence, and in 
other cases (vide Laccophilus) they are excessively fine and indistinct, and as a 
rule are most regular and highly developed in large and smooth species such as 
we find in the genus Cybister; as already remarked the outer series is more 
irregular and less persistent than the others, the sutural series being the most 
permanent. 
In the great tribe Hydroporides, the rule is that the upper surface of the body 
bears a true punctuation such as exists in many other families of Coleoptera, while 
on the other hand in the Colymbetides and Hydaticides, the opposite of this is the 
case—punctate species being exceptional. 
When present, the punctuation is of various degrees of fineness and coarseness, 
of density and sparsity, and is more usually seen on the elytra than on any other 
parts ; in many of the genera of Hydroporides, however, the hind cox are very 
persistently punctate. The most remarkable punctuation occurs in the genus 
Pachydrus, where certain species have a deep coarse punctuation on the wing-cases, 
the punctures moreover being more or less elongate in a peculiar manner. In 
many species of the genus Hyphydrus the elytra have a double punctuation, very 
fine punctures being mixed with considerably coarser ones. 
In the Agabini punctuation is nearly absent, the surface being either smooth, 
or—and this is the more frequent—covered with a very fine reticulation, formed 
by fine scratches placed so as to form meshes of irregular shape, and varying much 
from species to species. In Copelatus the sculpture is peculiar, and in its highly 
developed form consists of numerous longitudinal grooves or strize on the wing-cases 
arranged in a very regular manner. In the Colymbetides the most peculiar 
sculpture of the family is found: in Colymbetes the wing-cases are marked with 
transverse scratches, striz or grooves, placed very near to one another, and varying 
ereatly from species to species. In Meladema (vide M. coriacea No. 978) a still 
more remarkable sculpture exists; the elytra bear a large number of crescentic 
marks, which at the base are readily distinguished as such, but towards the 
extremity of the body become somewhat changed in shape and are very densely 
placed, so that an appearance is caused somewhat as if the surface were covered with 
overlapping scales. 
In the Hydaticides the surface is usually smooth, but in Eretes the wing-cases 
are marked with rather large quite round punctures, and in Acilius both the upper 
and under surfaces of the body are much punctate. In some species of Noterus 
there exists a peculiar punctuation consisting of large round isolated punctures 
placed chiefly on the hinder part of the wing-cases; and in Synchortus there is a 
somewhat similar sculpture, except that the punctures have their front margins 
somewhat raised giving rise to a peculiar rough appearance. 
It is worthy of notice that when punctuation is absent from the greater part of 
TRANS. ROY. DUB. SOC., N.S., VOL, II. 2D 
