NORSK ENTOMOLOGISK TIDSSKRIFT - Norsk entomologisk forening

106 Albert Lillel~ammer
Fig. 7. Flrrgstadbekken, lower part.
different. The distance from Storlidammen to Sudafjorden, where
the Storelva debouches, is about 20 km. The fall in height in
this part is 253 m. The upper part of the river is rich in falls and
rapids; the aspect of the lowest 5 km is as shown in fig. 6. In
May-September the pH values measured were from 6.2 to 6.5
in Suldalsl5gen and from 5.7 to 6.2 in Storelva.
Flergstadbekken obtains its water-flow from the lower mountain
areas in the same manner as Storelva. The water level in the
stream will therefore in its course follow Storelva rather closely.
The stream flows through a forest area having a boggy moor,
Flergstadtjerdng, from the ground water of which, it is presumed,
the stream receives some of its water-flow. At some places the
stream runs underground through falls of rock. The stones in
Flergstadbekken vary considerably in size; fig. 7 gives a characteristic
picture of its lower part. The stones to a large extent are
covered with moss vegetation.
The Material
During the investigation stress was laid on obtaining a rich
nymph material. Particularly for taxonomic reasons, it was of
considerable importance to obtain nymphs ready for emergence
so as simultaneously to be able to determine the insect by both
nymph and adult characters. Of most species, material was