234 PROCEEDINGS OF THE 



in northern Germany. Its occurrence in tlie north of Scotland 

 was therefore a thing not so improbable; but it is interesting 

 to find this boreal species appearing so far south as the S.W. of 

 Donegal. 



D. Lapponicus differs somewhat in its habits from marginalis 

 and its congeners. D. marginalis seems to prefer marshes and 

 ditches, where there are plenty of water plants; Lapjmiicus chooses 

 rather an open lake or tarn; at least the three times I have met 

 with it, the pieces of water have been almost devoid of vegetation. 

 But while Lapponicus dislikes botany, it makes selection as to 

 geology. A soft and muddy bottom does not suit it; it always 

 chooses a lake where there are plenty of stones, and it is the 

 observance of this fact which has enabled me to take it pretty 

 freely. Instead of sweeping along the banks of the tarn, or 

 scouring the bottoms of pools with the net, my plan is this: — 

 Going to the shallow and stony end of the lake, and putting 

 myself into the condition of a heron, I carefully turn over the 

 stones, causing as little disturbance as possible, and there beneath 

 the stones, or clmging to them, the insect is found, I have taken 

 as many as four beneath one stone. They seem capable of taking 

 very long breaths, or else of collecting oxygen from the diminu- 

 tive vegetation which clothes the stones, as I have very seldom 

 observed them coming to the surface to breathe. 



I would infer from this habit of lurking beneath stones that 

 D. Lapponiciis may probably be nocturnal in its habits, as is known 

 to be the case with another water-beetle, Orechtochihis villosus, an 

 insect allied to the Gijrini. 



D. Lapponiciis seems to be very local, and, it might almost be 

 added, gregarious; for while it occurred freely in one tarn, I 

 searched several others in the neighbourhood without success. 

 It is also remarkable that in the loch where it was obtained, there 

 were very few, I might say almost no other insects, although in 

 the neighbouring peat-holes Hijdropori, Gyrini, etc., were plentiful. 



Another fact which struck me was, that in the lake only D. 

 Lapponicus occurred, Avhile a few yards farther up the hill, on 

 putting the net down into a mass of floating water plants, the 

 first haul brought up four or five Dytisciis marginalis, which looked 

 quite gigantic beside their lake cousins. There was no marginalis 

 in the lake, only Lapponicus, and no Lapponicus in the peat-hole, 

 only margimilis. 



