On Aquatic Carnivorous Coleoptera or Dytiscide. 203 
later acquisitions, and so go back step by step till we reached the striation in its 
rudimentary form, we should find it similar to, but not identical with, that of other 
species ; which is equivalent to saying that each species has had a truly separate 
line of development. 
_ As a striking instance of the probable truth of this atatanent I would point to 
the New Caledonian Copelatus aubei—the species in which the striation of the 
elytra reaches its maximum. The locality where it is found is remarkably rich in 
possessing very different forms of the genus; one of these forms C. interruptus 
(No. 847) has a striation of the elytra quite peculiar to itself; the strize are twelve 
in number but they are fragmentary, and slightly irregular in a peculiar manner. 
Now the only other species having so many as twelve strie is the C. aubei above 
alluded to, and on examining this species one is brought to remark that on the 
portion of the wing-case where the striz are usually least perfect—the apical 
portion—they show a fragmentary condition similar to what exists over the whole 
elytra in C, interruptus. In addition to this there is a true highly developed 
submarginal stria in C. aubei, and in C. interruptus, this stria is not present but 
is represented by a regular series of punctures, which only require extension to 
form the stria as seen in C. aubei. Now both these species are highly developed 
ones, found in one (isolated) locality, and the conclusion that their similarities are 
due to similarity of environment, and their differences due to a different condition 
of more oriyinal punctuation, is perfectly satisfactory to my mind. I conclude that 
C. interruptus and C. aubei have been developed from similar (but not identical) 
primitive conditions ; and that the serial punctures which seem to determine the 
lines of development of the striation, were less regular in the primitive ancestors 
of C. interruptus, than they were in the primitive ancestors of C. aubei, and that 
as the resultant of this the former species as we now see it has less regular 
striation than the latter has. 
The Heap in the Dytiscide is of remarkably short, broad form, and is inserted 
on the prothorax in such a manner as to completely fill up the front part of the 
latter and so avoid any discontinuity of outline at the junction of the two; it is 
considerably broader than long, and in Laccophilus, where the abbreviation is 
greatest, the width is about double the length; its upper surface shows but 
little convexity, and is marked on each side, near the front, at a little distance 
from the inner margin of the eye, with an irregular depression or fovea; and 
close to the suture with the labrum there is a transverse depression or short 
impressed line on each side; the clypeus is nearly always so completely joined to 
the posterior portion of the head, that the suture between the two is obliterated, 
although frequently its commencement can be traced near the eye, on each side, 
whence it extends inwards towards the anterior part of the irregular depression 
before alluded to; in the genus Dytiscus (as also in Pelobius) the clypeal suture 
is distinct across all the width of the head, and in Meladema (especially in 
TRANS. ROY. DUB. SOC, N.S., VOL. Il. 25 
