I 6 CHAPTER I 



Only animals living (breeding) on the continent of both Europe and North 

 America were considered. A species occurring only on the Bermudas or on the 

 arctic islands of Canada as well as in Greenland, is not counted as "American"; 

 similarly, a species confined to Iceland, the Faroes, Jan Mayen, and (or) Spitz- 

 bergen, not as "European". The British Isles, however, are counted as belonging 

 to the European continent. 



Freshwater animals occurring also in the sea, or regularly descending into the 

 sea, are omitted. 



Not included in the list are furthermore the following types of animals: 



a. Domesticated animals. An enumeration is superfluous. 



b. Animals introduced and released for the purpose of game, fur, or fishery. 

 Examples: American Mink (Mustela vison Schreb.), Muskrat {Ondatra [Fiber] 

 zibethica L.; fig. 5), and Rainbow Trout {Saltno irideus Gibb., s.l.), in Europe; 

 European Hare {Lepus europaeus Pall.), and European Saibling [Salvelinus al- 

 pinus L.) in North America. 



c. Animals used in "biological control" of noxious insects, plants, and 

 other pests. Besides instances mentioned below (p. 121 a.f.), leaf-beetles of genus 

 Chrysomela (Chrysolina) were imported to California against the European weed 

 Hypericum perforatum (St. John's Wort). 



d. "Pet animals", imported and released, for instance in order to still the 

 nostalgia of emigrants. Examples: Starling {Sturnus vulgaris L.; fig. 4) and 

 English or House Sparrow (Passer domesticus L.), in North America; the American 

 "Robin" (Turdus migratorius L.), in Great Britain. 



e. Animals imported for study or fancy and unintentionally escaped. Example: 

 the Gypsy Moth (Lymantria dispar L.) 1868 or 1869 in North America, and prob- 

 ably several freshwater animals, released by aquarium fanciers. 



f. Unintentionally imported animals which have not become established in 

 the new continent. Most of them have been found in ports or in wares immediately 

 after these have been unloaded, especially on the quarantine stations. Therefore 

 the majority of cases reported by Kraepelin (1901) from Hamburg have been 

 neglected whereas species found in hothouses (Kew Gardens, &c.) were considered. 

 Several similar cases, however, may have been overlooked. 



Summarising, the list below tries to give, within the animal groups considered, 

 all species common to Europe and North America, and breeding (or supposed to 

 breed) in both continents, which are not purposely brought across by man in 

 either direction. 



Species believed or stated to be unintentionally introduced into either or 

 both continents are indicated by a cross (f), in doubtful cases put in brackets. 



