960 On Aquatic Carnivorous Coleoptera or Dytiscide, 
coxal lines are not greatly turned outwards towards their termination then the 
supra-articular border 1s very broad. 
There are no stigmatic rugee on the first ventral segment, and the terminal two 
stigmata are small or of moderate size, The swimming legs are highly developed, 
but vary much in this respect, being in certain forms rather elongate and slender, 
in others short and thick; their tarsi are always terminated by two very distinct 
nearly straight claws, which may both be elongate, although the upper or outer 
one is usually much shorter than the other; the hind margins of the four basal 
joints of these hind tarsi are furnished with beautiful cilize or elongate scales which 
are set close to one another, and overlap the following joint, to the surface of which 
they are so extremely closely pressed that they scarcely interfere with the perfect 
smoothness of the face of the tarsus; their scales vary greatly in the tribe, but 
they are always conspicuously present, and occur in no other water beetles out of 
the tribe. In Eretes they are short and broad, and form a single series, and as 
they are easily removed by friction with a hard surface, they may escape detection 
in it, but ever when quite removed by illusage there remains a series of punctures close 
to and parallel with the hind margin, marking their points of insertion and so indi- 
cating their existence in an incontrovertible manner. In the species where they 
are most highly developed as in D. vittatus (No. 1049), they are very conspicuous, 
and arranged so as to form an arch, and are so extensive so to cover quite one-half 
of the area of the outer face of the tarsus. 
In many other respects there occurs a considerable amcunt of variation in the 
structure of the Hydaticides, and the greater part of these exceptional features 
occur in Hretes; some have been noticed in the description of that genus, but 
others still require mention. In all the Thermonectini and Hydaticini the anterior 
and middle legs are separated by a considerable space, but in Eretes they are much 
more contiguous, and this difference is accompanied by some important correlative 
discrepancies in the structure of the adjacent parts. The front of the prosternum 
in Eretes shows a kind of longitudinal face in the middle, placed nearly at right 
angles to the plane of the prosternal process (and so simulating to a superficial 
observation the prothoracic structure of the Hydroporides); whereas in Acilius and 
Hydaticus there is no trace of this longitudinal thickening of the middle of the 
front of the prosternum. In C&thionectes however, the prosternum is greatly 
incrassate along the middle and compressed, and a similar structure, though not 
developed to so great an extent, is approached by some other Thermonectini. ‘Ihe 
prosternal process is acuminate, narrow, and elongate in Eretes, whereas in all the 
other genera it is short and broad and obtuse or rounded: the inter-coxal process 
of the metasternum is marked with an elongate narrow groove in Eretes, and only 
connects in an imperfect manner with the mesosternal fork, whereas in the other 
members of the aggregate the connection with the wesosternal fork is intimate and 
perfect, and the depression for the prosternal process is peculiarly short, broad and 
