THE AQUATIC COLEOPTERA OF THE NORTH EBUDES 215 



species. H. morio occurred in many of the pools, but always 

 in small numbers. A little farther on at 1200 ft. is another 

 extensive " plateau " with numerous pools, and here H. morio 

 was common, while, after much work, I could only find a 

 single specimen of H. gyllenhalii. In Skye and Eigg this 

 latter species was not dominant, as it only occurred in 37 

 and 30 per cent respectively of the collections-, but H. morio, 

 owing to the absence of higher ground, was not there to take 

 its place. 



The case of A. arcticus is interesting as being an example 

 of a species truly " limno-oxylophile " in this district, whereas 

 it is not so restricted in many other localities. I found it 

 commonly in July 1905 on Rannoch Moor (Perth Mid) at 

 about 950 ft. in the peaty pools, and also at Aviemore 

 (Easterness) in June and July 1904 it occurred in many of the 

 pools at elevations of 1600 ft. and over. Apparently the 

 explanation of this fickleness is that below a certain elevation 

 varying, of course, in different localities the species is 

 excluded from the pool association, and only in the higher 

 and colder places can it force its way into that group. The 

 same remarks also apply to Deronectes griseostriatus, which 

 at high elevations invades pools as well as lochs. 



What I have said here concerning the associations of 

 Water-beetles is deduced from somewhat meagre and incom- 

 plete material, but it seems to me that what is being done 

 by the cecological botanists is equally capable of being done 

 by zoologists, especially in groups where statistical results 

 can be accumulated. I hope later to deal with the subject 

 of the associations of the Aquatic Coleoptera more fully. 



The only helophile (Fresh-water marsh) habitat which I 

 found on Eigg was a few small grassy pools below Kildonnan 

 and just on the edge of the rocks at the shore. Here, H. 

 discretus, H.fuscipes, //. brevipalpis, and C. orbiculare occurred. 

 A single specimen of //. lituratus occurred at the same place, 

 and was the sole representative of the halophile (Salt marsh) 

 group, for which there seemed to be no suitable ground. 



The interesting question as to whether these few pools 

 at Kildonnan hold the remnants of a once extensive helo- 

 phile fauna, or whether they represent the first foothold of 

 species which have recently invaded the island, cannot be 



