The relationship between the palaearctic and nearctic faunas 253 



The theories of earlier transatlantic land-connections 



The Iceland — Greenland bridge 



It may seem inconsistent, after the existence of a biologically efficient land- 

 connection between Europe and North America has been denied or at least 

 considered highly improbable, to raise again the problem of a "land-bridge" 

 within the North Atlantic region. Land-bridges, however, are not bound to join 

 continents, they may be, or have been, "blinds" connecting islands to a main- 

 land. 



Perhaps the situation is best made clear to the reader in the form of a brief 

 account, brought up to date, of the zoogeographical conclusions to which the 

 present writer arrived (193 1) from a study of the insect fauna of Iceland, all the 

 more as later students have agreed, at least in the essentials. 



The fauna of Iceland is practically purely European, the American element being 

 restricted to some few species: the Noctuid Moths Crino sommeri Lef., Crymodes 

 exulis Lef., Rhyacia (Caradrina) quadrangula Zett. (figs. 36-38), and the Gnat 

 ("Black Fly") Simulium vittatum Zett. (fig. 39), all of them no doubt able to arrive 

 by air under present conditions. Possibly the Empidid Fly Rhamphomyia hirtula 

 Zett. (Greenl., Icel., Scotl.) belongs to the same group. The Icelandic form of the 

 Water-beetle Colymhetes dolabratus Payk., thomsoni Sharp, is decidedly more re- 

 lated to the sbsp. groenlandicus Aube, of Greenland and North America (Brinck, 

 1940, p. 37-40) and must likewise have invaded Iceland from a western direction, 

 by air or with drifting ice. The same is true for a genuine fresh-water animal, the 

 small Copepod Diaptomiis minutus Lilljeb., a Nearctic species, known also from 

 Greenland (Poulsen, 1939, p. 29). 



Even among breeding birds, only three Icelandic species are of clearly Nearctic 

 origin: Biicephala islandica Gm., Gavia (Colymbus) immer Briinn., and Histrionicus 

 histrionicus L. (Timmermann, 1938-49, p. 123). 



As far as vascular plants are concerned, Epilobiutn {Chamaenerium) latifolium L. 

 and two Orchids, Habenaria (Leucorchis) hyperborea L. and H. (L.) straminea 

 Fern., belong to an American element (the last-named also reaching the Faeroes). 

 All of them have seed excellently suited for wind-transport. Lowe (1950) has added 

 some forms of doubtful taxonomic position, including polyploids, the historical 

 interpretation of which is most delicate since a polyphyletic origin cannot be dis- 

 missed. 



In all, this is a poor share of American inhabitants indeed for an island situated 

 900 km. or more from the British Islands and Scandinavia, but only 330 km. from 

 Greenland which, in its turn, is separated from southern Baffin Island by the 



