934 On Aquatic Carnivorous Coleoptera or Dytiscide. 
between the broad form displayed by the pieces in the Agabini and the narrow one 
usually found in the Colymbetini. Thus in Matus the side piece of the fourth 
segment is as broad as in the genus Agabus, while in Coptotomus it is hardly broader 
than it is in certain members of the Colymbetini (Dytiscus grapu, No. 948, for 
example). [n this respect therefore these genera connect the Agabini and Colymbetini. 
In most of the several genera the posterior portion of the metathoracic epister- 
num where it is exposed between the wing of the metasternum and the epipleura 
is very attenuate and acuminate; this is especially the case with Copelatus, Aglym- 
pus, Lacconectus, and Matus; while in Coptotomus the wing of the metasternum 
has so great an outward extension that it is almost invaded by the epipleura, that 
is to say that its termination cannot certainly be distinguished without slightly 
raising the epipleura from the breast. Thus this genus which by its ventral side 
pieces approximates to Culymbetini, by its metathoracic structure departs most widely 
therefrom. On the other hand Lancetes has the posterior extremity of the epister- 
num comparatively broad, and the apex of the wing of the metasternum distinctly 
though slightly separated from the epipleura, thus making an approximation to the 
Colymbetini. : 
In these genera, the setigerous abdominal pores, relied on by Thomson as 
distinguishing the Agabides from the Colymbetides, undergo much variation ; they 
are distinct on the fourth and fifth segments, but are wanting on the third in 
Lancetes and Coptotomus ; they are present on the third, fourth, and fifth segments 
in Matus, but are only very slightly impressed ; they are present on the three seg- 
ments but are very small in Copelatus and Aglymbus; in Lacconectus they are 
also present but are so minute and rudimentary that they can scarcely be detected; 
and in Agabetes they are altogether wanting. 
IJ. 11.—Group Cotymperint. (Vide p. 605.) 
This aggregate is formed by four genera (comprising sixty-two species) ; the 
individuals are of moderate or rather large size, varying from 8 to 21 m.m. in length, 
and the surface is not punctate, but is either nearly smooth or possesses on the 
wing-cases a peculiar sculpture, which may be either reticulation or transverse 
scratching (aciculation), or even a kind of faintly raised sculpture having a slightly 
imbricate appearance. ‘The semimembranous side piece of the first segment of the 
hind body (i.e., the part interposed between the stigma and the edge of the ventral 
plate) is marked by transverse rugee or furrows; when there are any setigerous 
punctures on the hind femur, they form an irregular patch at the extremity, not 
however close to the hind margin, but widely separated therefrom. 
The most important of these characters is the presence of the stigmatic rugee, and 
it is the possession of these rugze that decides absolutely that a species shall be placed 
in the Colymbetini rather than in the Agabini. These rugze are found outside the 
limitsof the Colymbetini only in the two genera Hyderodes and Dytiscus (forming the 
