The relationship between the palaearctic and nearetic faunas 



249 



FIG. 35. World distribution 

 of Ponera coarctata Latr., 

 no doubt an old species, 

 belonging to a very primi- 

 tive group of ants. 



1 = forma typica 



2 = sbsp. pennsylvanica 



Buckl. 



3 — sbsp. boerorum Forel 



4 = sbsp. mackayensis Forel 



The figured worker (from 

 Smith, 1947) is of sbsp. 

 pennsylvanica. 



Isles directly from parts of North America inhabited by the plants considered, 

 that is, not north of Newfoundland. No bird has a normal route of migration like 

 this, it is a question of abnormal movements or pure wind-drift. 



Now, Williamson (1954) has given a very interesting report of occasional 

 appearances of American birds in the British Isles in the fall of 1953 and, what is 

 more important, has been able to correlate the observations with the meteorological 

 situations preceding the influx of these birds (fig. 34). Their route appeared as a 

 clear wind-drift and the offshore drift on the American side, according to the 

 weather, at least in one instance could have taken place as far south as Cape Hat- 

 teras. The American birds noted in Great Britain and Ireland, on this and other oc- 

 casions in late years, include geese, ducks, waders, passerines, cuckoos &c. (Alex- 

 ander & Fitter, 1955) and Williamson (I.e., p. 26) speaks of "the now regular 



annual occurrence of nearetic waders at English reservoirs and sewage-farms". Is 

 the sudden appearance of the American freshwater snail Lymnaea catoscopium Say, 

 in "a warm engine-pond in a timber yard", in Leith, Scotland (Kevan, 1943), 

 possibly to be explained in this way, and not through human transport? 



The direct transatlantic bird-connection, direction east, is accidental but not 

 too scarce. How great is the chance of these birds coming into contact with dia- 

 spores of the discussed plants? Heslop-Harrison (I.e., p. 114) stresses the point 

 "that they are all aquatic, marsh or lake-margin plants". Though this statement 

 does not apply very well to the Sisyrinchium, which also takes a different position 

 in other respects, Heslop-Harrison is probably right in regarding this ecological 

 property of the group (equally relevant for Heteromeyen a ryderi) as an indication 

 in favour of bird-transport. The reasons seem to be: — 



