S42 On Aquatic Carimvorous Coleoptera or Dytiscide. 
acuminate spine; the front conse are very approximate, and the prosternum in 
front continues the plane of direction of the prosternal process ; the mesosternum 
is placed almost completely at right angles to the metasternum ; its epimeron is 
large, and very broad at the metathoracic-episternal angle; its fork is small and 
inconspicuous. The metasternum is elongate in the middle, but excessively 
reduced at the side ; it approaches very near to the middle coxa, and is afterwards 
deflexed outside the anterior border of the hind coxa, forming a slender very curved 
band ; the inter-coxal process is very narrow owing to the great approximation of 
the middle coxee, and is curved up in front to form a minute but perfect articulation 
with the mesosternal fork, it is marked by a very fine groove (of variable length) 
for the reception of the extremity of the prosternal process. The hind coxe are 
of enormous size, and extend greatly forwards so as to possess an extremely arched 
anterior border ; the coxal lines are of peculiar form, they are very distinct, and 
commence in front at the apex of the metasternum being there much approximate 
to one another, they extend backwards, diverging from one another till each reaches 
the outer hind angle of the process; the two processes are completely soldered 
quite to the hind margin, which thus presents a truncate edge ; the coxal border is 
very distinct and definite, it is broad in front but terminates in a point behind : 
the coxal cavities are completely contiguous and very much concealed and protected 
by the processes ; no coxal notch can be detected, unless a slight sinuation of the 
hind margin of the process be considered to represent it. The anterior and middle 
legs are feeble, their tarsi conspicuously 5—jointed and without any trace of lobing 
of the third joint. The swimming legs are highly developed and powerful, their 
femora are broad and are laminate at their hinder outer angle, which is nearly a rect- 
angle and well marked ; the tibize are short and stout, much shorter than the femora, 
and terminated by two sublinear highly developed spurs, which are not acuminate, — 
but are minutely emarginate at the extremity; the tarsi are of peculiar and 
characteristic form; when their outer or upper face is observed it is seen that the 
hind margin of each joint deviates greatly from a straight line, the outer portion of 
the joint being produced backwards, so as to form a kind of lobe projecting over the 
following joint; the basal joint is about as long as the two following ones together, 
the terminal one is broad, and bears a single short stout claw. 
The abdominal stigmata are all small and circular. 
The male tarsi are but little developed, sometimes it is not easy to distinguish 
any difference between their structure and those of the female ; they show very little 
dilatation and when they are thickened the incrassation is quite as great in the 
vertical as it is in the horizontal direction; no sexual sculpture has been detected 
in the female. 
An interesting feature in certain species of this genus is the existence of a stridu- 
lating structure consisting of a curved series of grooves on the hind coxa; these 
are played on by a single, very obscure elevation situated on the anterior edge of 
