THE AQUATIC COLEOPTERA OF THE NORTH EBUDES 213 



adopting the definition of this term used by the cecological 

 botanists but contains at least two associations, one 

 characteristic of the bog-pool habitat, the other of the lochs 

 of the peat moors. Species belonging to one of these 

 associations will often be found associated with species of 

 the other association, since the two habitats obviously merge 

 in places. For instance, there are few highland lochs 

 without at least some Sphagnum patches round their margins, 

 and these patches will usually contain some of the pool 

 species ; also it is difficult to decide between a large pool 

 and a small lochan. Even so it is probable that some 

 species are more restricted to actual pools than others. For 

 instance, H.gyllenJialii seldom occurs in lochs, while H. obscurus 

 is much less particular. If we compare the associates of the 

 H. gyllenhalii with those of a species such as D. griseostriatus, 

 which, in our district, only occurred in the lochs, this point 

 is clearly seen : 



Associates of H. gyllenhalii. 



SKYE and EIGG. 

 19 collections. 31 species. 



Associates of D. griseostriatus. 



SKYE and EIGG. 

 6 collections. 22 species. 



H. pubescens 



A. bipustulatus 



A. globulus . 



H. tristis 



Ph. melanocephalus 



H. obscurus . 



H. viridicollis 



H. erythrocephalus^ 



H. nigrita / 



H. morio "^ 



G. natator 



L. truncatellus j 



H. brevipalpis J 



A. sturmii 



I. fuliginosus 



Rh. bistriatus 



Ph. minutus 



H. lineatocollis 



D. assimilis 



D. griseostriatus 



per cent. 

 100 



95 

 79 



74 

 68 



63 



47 



2 I 



16 



1 1 



A. arcticus . 



H. obscurus ^ 



A. bipustulatus J 



H. erythrocephalus 



D. lapponicus 



A. sulcatus 



G. natator 



L. truncatellus 



H. tristis 



Rh. bistriatus 



D. punctulatus 



Ph. melanocephalus 



A. globulus 



H. fulvus 



D. assimilis 



H. gyllenhalii 



H. pubescens 



A. sturmii 



I. asnescens 



Rh. exoletus 



per cent. 

 IOO 



3 3 



68 



5 



33 



