8 54 On Aquatic Carnivorous Coleoptcra or Dytiscidce. 



I. 23.— Genus HUXELHYDRUS. {Vide p. 369.) 

 Under this name T 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 elongate, 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 ^. 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 Carabida3 : and behind the front coxse 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 coxae are quite contiguous ; the hind coxae 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 hind legs are slender, and are formed 

 much as in Bidessus. 



Takinsf all these characters into consideration this little insect would seem to be 

 one of the most anomalous of the Dytiscid:© ; the prosternal process failing to connect 



