144 Flemiptera-fleteroptera. 
HYDROMETRID Z. 
This family is composed of various genera, some of 
which seem to me to have very little in common; they 
may, however, all be said to be subaquatic. Aépophilus is 
perhaps the most aberrant, its contiguous coxe and Lygzid 
antenne giving it an aspect quite foreign to the other 
members of the family. Mesoveliu, again, has almost con- 
tiguous coxe, but the antennez are very different from 
those of Aépophilus. The extraordinarily produced face of 
Hydrometra is utterly unlike that of any other of our 
genera; they, however, have a few features in common ; 
they all have the elytra of one texture throughout, and 
undivided into corium, clavus, and membrane, and the 
underside clothed with white silvery pubescence, which 
is no doubt impervious to water, and are destitute 
of odoriferous sacs. The habits of Aépophilus and 
Mesovelia are at present very little known; the former 
is a submarine species, occurring under stones, etc., 
below high-water mark. Mesovelia, according to Sahl- 
berg, occurs on the leaves of Nymphea, Potumogeton, 
etc. The other genera of the family live on the surface 
of the water. The members of this family are carni- 
vorous. 
TABLE OF SUBFAMILIES. 
(4) 1. Coxe contiguous or nearly so, scutellum 
visible. 
(3) 2. Ocelli absent : ‘ : ‘ ; . ABPOPHILINA. 
(2) 3. Ocelli well developed . : MBsSOVELIINA. 
() 4. Coxe widely separated, seutellum covered. 
(6) 5. Head very elongate in front of the eyes, 
many times longer than wide, and widened 
towards the apex. HyYpRoMETRINA. 
(5) 6. Head short, as wide across the eyes as long. 
(8) 7. Posterior femora not reaching to the apex of 
the abdomen . VELIINA. 
(7) 8. Posterior femora very long and thin, reach- 
ing far beyond the apex of the abdomen. GERRIDINA. 
