io6 THE SCOTTISH NATURALIST 



THE AQUATIC COLEOPTERA OF THE 

 OUTER HEBRIDES. 



By Frank Balfour Browne, M.A. (Oxon. et Cantab.), 



F.R.S.E., F.Z.S. 



^ {Concluded from page 92.) 



The richest collection on the island was made in one of 

 these roadside ballast-pits, which had on it a good growth of 

 glyceria with one or two quite small patches of Sphagnum 

 at one side. The fauna of this small pond was as follows : — 



This is distinctly a mixed community, several of the typical 

 peat-pool species being absent, e.g., //. obscufus, A. globulus, 

 Ph.fuscipennis, and H. viridicollis, while H. gyllcnhalii was 

 scarce. On the other hand, several of the loch species were 

 present, e.g., H. ruficollis, H. ivehnckei, H. pabistris, and 

 A. sturuiii. As a rule, Haliplus lineatocollis and Helophorus 

 aqualicus were present in these glyceria ponds, but in this 

 particular case both were absent. 



The fact that these ponds become stocked with wate^r- 

 beetles shows that there is a constant — or perhaps a periodic 

 — movement of these insects in the island. Individuals 

 arrive from various directions, and a struggle between the 

 different communities develops, and that community ulti- 

 mately survives which is best adapted to the particular 

 type of habitat. Since these ponds — I suppose invariably — 

 end as peaty pools, the struggle amongst the water-beetles 



