A GUIDE TO THE STUDY OF BRITISH WATERBUGS. 113 



4. Ocelli absent ; antennae long and thick. Marine. 



Found under stones, etc., below high-water 



mark Aepophilus. 



— Ocelli present ; antennae long and slender. Fresh- 



water. Found on Potamogeton, etc., in ponds 



and canals (fig. 6) Mesovelia. 



5. Prosternum, mesosternum, and metasternuni more 



or less equal to one another, all well developed 

 (fig. 3) ; posterior femora not reaching apex 

 of abdomen 6 



— Prosternum and metasternum very short, rneso- 



sternum generally much longer than the other 

 two sterna together (fig. 11) ; posterior femora 

 reaching far beyond apex of abdomen Gerris. 



6. Elongate; first segment of antennae long, curved ; 



anterior tarsi with three distinct segments 



(fig. 4) ... Velia. 



— Short ; first segment of antennae short ; anterior 



tarsi with one segment and two minute 

 "nodes" between the tarsal segment and the 

 tibia Hydroessa. 



Hydroessa Burin. 1835 (= Microvelia Am. & Serv. 1843)* 

 bears a striking though superficial resemblance to Hebrus. There 

 is only one British species, viz. H. pygmaea (Dufour), figured in 

 the British works above-mentioned. It has also been described 

 under the names reticulata and pusilla. The apical segments of 

 the venter ( $ and ? ) are figured here on Plate I., figs. 12 & 13. 

 It is gregarious and widely distributed from Perth to Hamp- 

 shire and from Norfolk to Armagh, though it can scarcely be 

 considered common. The macropterous form is rare. I found 

 a small colony in a large reed-fringed pond in Woolmer Forest 

 (Hampshire) on Easter Monday last, and observed them for a 

 little over half an hour in their natural habitat. Unfortunately, 

 I was not able to stay longer (having to return from a short 

 holiday), but I captured a few individuals to continue my obser- 

 vations upon them — and they are now before me. 



They were assembled in a small inlet fringed exteriorly with 

 reeds, a luxuriant mass of Sphagnum concealing the margin of 

 the pond. In the water were masses of Ceratophyllum demersum 

 (horn wort). The tiny blackish insects, specked with pale bluish, 

 are very conspicuous in the water ; they disdain any foreign 

 support as they move about — so lightly that there is scarcely 

 even the slightest dimple impressed on the surface. Their gait 

 may be described best as a "scuttle," a series of very quick, 



■■'■Microvelia was founded by Westwood in 1834 (Ann. Soc. Ent. France), 

 as a section or subgenus only ; he refers to the species as " Velia pygmaea" 

 or " Velio, (Microvelia) pygmaea " throughout. 



