296 The It ish Naturalist* September, 



total these " visitors" would also greatly affect the results. 

 As an instance, I have described the West Cork records as 

 including only peat-moss and running-water habitats, yet 

 Hydropotus paluslris, L., actually occurred in four out of eight 

 (50 per cent.) of the collections made in that district, it being 

 neither a member of the peat-moss association nor of the 

 running-water association. 



With regard to the four species new to the Irish list — 

 Agabus co?ispersus, Marsh., was quite common in the br.ickisk 

 part of the Youghal marsh, and it also occurred at Kinsale. 

 It is therefore undoubtedly a native. The other three 

 species, Cymbiodyta ova lis, Thorns., H eloc hares pun da tics, Sharp, 

 and Helophorus affinis. Marsh., were only represented by a 

 single specimen in each case, and I am not inclined, upon the 

 record of a single specimen, to consider them as Irish species. 



A single specimen of another species, Hydroporus celatus, 

 Clark., previously recorded in Ireland only from Derry, 

 occurred at Kinsale. The Britannic distribution of this species 

 is somewhat curious, and I think that, in England at least, the 

 records are largely those of single specimens. It has 

 apparently occurred in Cornwall and Devon, Sussex and 

 Surrey, Essex, Cambridge and Leicester, Lancashire, York- 

 shire and Northumberland. In Wales the only record is for 

 Carnarvon. 



The Scottish records are for Kirkcudbright, Edinburgh, 

 Perth, Aberdeen, Shetland, Arran, and Dumbarton. I found 

 it fairly commonly at about 1,000 feet elevation in the latter 

 county, but the Arran record rests on a single specimen which 

 I took last year on Goatfell. These mountain specimens differ 

 from the Kinsale one in being considerably smaller, and they 

 approach Hydroporus monticola, Sharp, in shape. The Kin- 

 sale specimen, however, agrees with Surrey, Sussex, and 

 Cambridge specimens which I have seen. I have to thank 

 Dr. Sharp for confirming my identification of this specimen. 



The whole question as to how one is to decide which species 

 are denizens and which are chance visitors is a very difficult 

 one in studying the geographical distribution of any group, 

 but it is, perhaps, one which might be settled by an exchange 

 of views among those interested in the subject, and it is 

 certainly one upon which there should be a general under- 

 standing. 



