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On Aquatic Carnivorous Coleoptera or Dytiscide. 
I. 3.—Genus HY DROCOPTUS, (Vide p. 261.) 
This aggregate is formed by five species ; the individuals are of quite small size, 
(only 2 m.m. long), oblong-elliptic, and transversely convex in form, without: 
pubescence and of a yellowish colour, with the elytra a little darker, and subject to 
being marked with very indefinite large yellow patches, or vitte. Their antennz 
are short and rather stout and very nearly simple, the middle joints being just 
visibly broader than the others. The labial palpi are not dilated, although their 
apical joint is just visibly thicker than the others. The prosternum in front of the 
coxee is rather large, and along the middle is in one plane from the front to the 
termination of the prosternal process ; this latter is small and narrow, its extremity 
obtusely acuminate. The front tibize are moderately stout and bear a few long 
spines or setze on the outer edge, and are armed at the apex with two distinct 
spurs, one of which is longer than the other and very slightly curved; the front 
tarsi are simple and slender, and I believe without sexual difference: the hind 
coxee at their insertions are very distinctly separated. The swimming legs are 
slender, the hind margin of the femora furnished with a few distant short setze, which 
scarcely extend to the apex ; the tibize are slender ; the tarsi slend2r, about as long 
as the tibize, terminated by the two small equal, curved claws. 
The species assembled under these characters may perhaps prove to form more 
than one genus; Nos. 8 to 10, have the hind coxal processes but little developed, 
their outer apices being neither produced nor acute ; the other two species I have 
only been able to examine very imperfectly ; H. bivittis has the coxal processes 
more developed, so that their produced outer apices are very acute; while H. 
seriatus appears to be intermediate be'ween this latter species and the others in 
this respect. 
As it stands, the genus is represented in Australia, the Indo-Malay region, and 
Madagascar. 
The genus is interesting from the analogy it displays with Hydrovatus; an 
analogy which evidently arises from the two being in an approximately similar 
stage of evolution. We have in Hydrocoptus, the characteristics of the higher 
genus Noterus displayed in a far lower stage of evolution; 1 have not however 
associated the genus with Noterus in the second synthesis, but have at present left 
it isolated ; it seems to me probable however that it is really connected with the 
Noterini, by Pronoterus as an intermediate form, and if so the genus will be 
correctly placed in the Noterini; as however I have been unable to find any trace 
of a curved spur on the front tibia, and as this character is so prominent a feature 
of the other Noterini, I have not associated Hydrocoptus with them at present. 
The name Hydrocoptus has never hitherto received any definition, although it 
was proposed in 1853, by Motschoulsky : in his Catalogue of Hydrocanthares de la 
Russie, he included under Hydrocoptus, the greater part of the Kuropean Hydro- 
pori; but in 1859, he described three species of the aggregate T am at present treating 
of under the generic name of Hydrocoptus (Ktudes Ent. 1859, p. 48, 44) ; and I have 
