On Aquatic Carnivorous Coleoptera, or Dytiscidw. 203 



later acquisitions, and so go back step by step till we reached the striatiou 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 statement, 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 diffei'ent forms of the genus ; one of these forms C. interruptus 

 (No. 847) has a striation of the elytra quite peculiar to itself; the striae 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 strios 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 stritie 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 original punctuation, is perfectly satisfactory to my mind. 1 conclude that 

 C. interrujjtus 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 Head in the Dytiscidee 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. BOY. DUB. SOC , N S., VOL. II. ' ^ 



