THE NORTH AMERICAN SPIDER FAUNA 263 



in the Holarctic Realm. It makes up a very substantial percentage of 

 the fauna of Canada and most of our states: about 30 per cent in 

 New York State, 47 per cent in Alaska, similarly high percentages 

 in the north woods of Canada, and 54 per cent in Greenland. The 

 representation decreases toward the south, to about 16 per cent in 

 Georgia, with even smaller percentages in our southwestern states. 

 In Europe the Linyphiidae are similarly abundant, with 29 per cent 

 in France, 43 per cent in the British Isles, and 41 per cent in Nor- 

 way and Sweden. In the tropics these spiders are largely replaced 

 by other types; in Brazil only 1.2 per cent of the total fauna belongs 

 to the Linyphiidae. 



The differences between the faunas of Europe and the United 

 States are largely due to those species, genera, and larger groups 

 that probably have been derived from the south, or represent a 

 remnant of the subtropical fauna that once occupied a more sub- 

 stantial portion of the temperate zone. In the United States most of 

 them occur in the southern states, or in the extreme southwestern 

 portion of our country; they make up what is often called a So- 

 noran fauna. In Europe a very similar fauna exists in the Mediter- 

 ranean subregion of North Africa. In both areas are found many 

 trap-door spiders and tarantulas, many large lycosids, pisaurids, and 

 ctenids, and representatives of tropical genera that have reached 

 their northern limits of distribution. For the most part, the animals 

 in the Sonoran region are closely paralleled by creatures of the 

 same genera or families in the Mediterranean region. A very few 

 major groups are represented in only one region; the families Dys- 

 deridae, Argyronetidae, Urocteidae, and Eresidae are largely miss- 

 ing from Nearctica; whereas the families Accatymidae, Hexuridae, 

 Hypochilidae, Plectreuridae, Diguetidae, Caponiidae, and Homal- 

 onychidae are almost exclusively North American. 



The following list shows graphically the similarities and differ- 

 ences in the spider faunas of the Nearctic and Palearctic regions.. 

 The figures for the latter are taken mostly from Eduard Reimoser's, 

 checklist of the Palearctic spiders. Those for the American column 

 are derived from various catalogues, but are also supplemented by 

 unpublished information. These latter are for the most part ap- 

 proximations of the true situation. 



