On Aquatic Carnivorous Coleoptera or Dytiscide. 907 
approximation to Agabus is undoubted, but the form of the prosternal process, and 
the ciliation of the hind margins of the swimming tarsi are quite those of Hydaticus, 
while the style of colour is quite foreign to Agabus. There is no reason therefore 
to look on the insect as in any respect a connecting link between Hydaticus and 
Agabus, nor as having any genetic connection therewith; it is really and truly a 
Hydaticinid, having some parts of its structure approaching to the structure of the 
like parts of Agabus. We may interpret this as an indication that it has had an envi- 
ronment, at certain periods of the history of the species, like thatof Agabus, but that 
on the whole the environment of the ancestry has not been dissimilar to that of 
Hydaticus. 
Although it must be considered as on the whole a lower form than Hydaticus, it 
does not display any special relations with the lower species of that aggregate : 
thus the lower species of Hydaticus have the eyes peculiarly small, while Prodaticus 
pictus has them larger than even the higher Hydatici; while its peculiarities of 
colour and form are not in the least approximated by the lower Hydatici; thus, 
although it must be considered the lowest form of Hydaticini yet brought to light, 
it displays no affinities whatever (except those of less evolution) with the next 
lowest forms of existing Hydaticini, and does not tend to suggest any descent from 
a common ancestor. 
It is worthy of remark that the colour is spot for spot the same as that of the 
North Australian Sandracottus guttatus. 
The insect is found in Persia or Northern India, a region lying between the 
region of Agabus, and a region where Hydaticus has a great development. 
I. 68.—Genus HYDATICUS. (Vide p. 648.) 
This aggregate consists of about forty-five species, whose individuals are of 
moderate size (one-third to two-thirds of an inch in length), of perfect form, with 
impunctate or polished surface, and with the upper surface variegate with black 
and yellow (only one or two exceptions.) The head has the antennal portion 
of moderate size or much reduced ; the eyes moderately large; the prothorax is 
without lateral margin. The anterior legs are separated by a rather broad space, 
and the prosternal process is distinctly but not greatly broader than this space, and 
is obtuse or rounded at the apex. The hind coxa is rather large, its front border 
is never very near the middle coxa: the coxal lines are quite distinct, and are only 
moderately turned outwards in their hinder portion, but mark off a broad supra- 
articuiar border, the coxal lobes are of about equal development in the transverse 
and longitudinal directions; there is a minute coxal notch. The swimming legs 
are highly developed, their terminal claws are nearly straight and the inner one is 
elongate, about twice as long as the other ; the upper face of their tibia has a series 
of large punctures, each of which bears a thick furcate seta, this series 
of punctures (in order to view which the marginal cilize must be elevated) extends 
TRANS. ROY. DUB. SOC., N.S., VOL. II. 6 A 
