The relationship between the palaearctic and nearctic faunas 251 



form a substitute. A further important peculiarity of S. angustifolium is its occur- 

 rence on the European mainland, most often regarded as escape from cultivation, 

 with one exception: in the Carpathians. According to repeated judgment (Lauter- 

 born, 1927, p. 84; Bocher, 1948, p. 15) the plant here gives the impression of 

 being indigenous. Serious consideration must therefore be given to the possibility 

 that the small European areas of Sisyrinchium angustifolium are actually pre- or 

 interglacial relicts, the remnants of a circumpolar area. At least, this hypothesis 

 seems more plausible for the Sisyrinchium than for Spiranthes romanzoffiana, as 

 emphasized by Hulten (1937, p. 132). 



There seems to exist on the American side a small European element of boreal 

 (non-arctic) plants corresponding to the "Americans" in Europe just treated. At 

 least Fernald (1925, p. 272 a.f.) regards a comprehensive group of such plants, 

 particularly in Newfoundland, as old relicts. The majority of these, however, are 

 no doubt late introductions (vide above, p. 146). Heslop-Harrison (1953, p. m) 

 maps two species, Carex hostiana D.C. (fulva Host.) and Potamogeton polygonifolius 

 Pourr. (oblongus Viv.), which he seems to regard as native in North America. Both 

 are restricted to Newfoundland (incl. St. Pierre-Miquelon) and either Anticosti 

 (C. host.) or Sable Island, Nova Scotia (P. polyg.). By Clapham, Tutin & Warburg 

 (1952, p. 1370) Carex hostiana is indicated as "probably introduced" in North 

 America. It may be appropriate to apply to the Potamogeton the suggestion of bird- 

 transport put forth concerning P. epihydrus above. A glance through the American 

 "Check-List" (1931) shows convincingly that stray birds on migration from Europe 

 are not uncommon on the Atlantic coast of North America.^ 



On the American side also, like Heteromeyenia ryderi in Europe, there seems to 

 exist at least one equivalent among animals, the fresh-water snail Lymnaea (Radix) 

 peregra Miill., known from only two localities on the Avalon Peninsula of SE 

 Newfoundland (Brooks & Brooks, 1940, p. 62). It is worth mentioning that the 

 appearance of the same species ("ovata Drap.") on small, new-formed islands 

 off the German Northsea coast was most likely due to bird-transport (Thienemann, 

 1950, p. 157). Also in other parts of Europe the distribution of this species gives 

 evidence for an extremely high power of passive dispersal and this property of 

 ubiquistic and more or less cosmopolitan fresh-water Molluscs is generally ex- 

 plained as the effect of transport with birds (Boycott, 1936, p. 123-126; Hubendick, 

 1947, p. 508-512, "limosa L."). 



Whether or not the isolated occurrence of the American Amphipod Gammarus 



^ The European birds most regularly observed on the Atlantic coast of North America are: 

 Branta leticopsis Bechst., Crex crex L., Lams minuttis Pall., Anas crecca L. /. typ., Erolia 

 alpina L. /. typ., Philomachiis pitgnax L., Scolopax rusticola L. /. typ., Vanellus vanellus L. 

 All are Swimmers or Waders. 



