854 On Aquatic Carnivorous Coleoptera or Dytiscida. 
I. 23.—Genus HUXELHYDRUS. (Vide p. 369.) 
Under this name J have separated a species that has in some respects the appear- 
ance of the members of Bidessus, and likewise is similar to that aggregate in much of 
its structure, it however departs from them by some very interesting characters; 
the prosternal process is much more largely developed and élongate, it is flat and 
only faintly margined at the sides; the mesosternum is joined to the metasternum 
at a very obtuse angle; the hind coxal cavities are more widely separated from one 
another: the coxal lines are extremely rudimentary, being very fine and short, and 
visible only in the immediate vicinity of the cavities. To these peculiarities may 
be added, as of minor importance, that the prothorax is straight at the sides or 
rather slightly narrowed towards the base, that the undersurface is densely, finely, 
and evenly punctured, and the elytra are truncate at the apices; and that the 
terminal joint of the front and middle tarsi is much more elongate than in any of 
the Bidessi. Many of the peculiarities of this insect are repeated to a greater or 
less extent in some of the Bidessi, and in the isolated Sternopriscus, and even in 
some of the Hydroporini. 
The Huxelhydrus syntheticus occurs either in Australia or New Zealand, and 
possibly in each of those regions. 
I have made this generic name, as well as Tyndallhydrus, Darwinhydrus, and 
Spencerhydrus, in reference to some men whose clear thinking and able writing 
have placed us under a load of obligation, my recognition of which I am glad to 
eXpress. 
I. 24.—Genus TYNDALLHYDRUS. (Vide p. 370.) 
A small species, of which only an unique individual is known to exist, is isolated to 
form this genus. At first sight one might fancy it to be an ally of Dytiscus 
duodecimpustulatus ( Hydroporini), but it is much smaller, and presents the 
remarkable character of having its prothorax narrowed behind, so that the outline 
is interrupted as in the Carabidee : and behind the front coxze the prosternal process 
is bent upwards, its apex is therefore concealed and is quite separated from the 
metasternum. The surface is densely punctate, and almost destitute of pubescence : 
the middle coxze are quite contiguous; the hind coxe are large, their front border 
having a great extension in the anterior direction ; the coxal lines are not turned 
outwards at the tip, and the coxal border is excessively minute ; the coxal cavities 
are rather widely separated, but a considerable approximation of their trochanters 
is possible inasmuch as the cavities have a distinct prolongation inwards, between 
the coxal process and the ventral segment; the hine legs are slender, and are formed 
much as in Bidessus. 
Taking all these characters into consideration this httle insect would seem to be 
one of the most anomalous of the Dytiscidee ; the prosternal process failing to connect 
