166 HENRIK W, WALDEN 



North Pacific route. The indications given by the land Gastropoda may be 

 kept in mind when discussing other animal groups for which one must depend 

 largely on the recent distribution, in the absence of fossil evidence. 



Finally, two further genera, Catinella and Coilostele, are common to 

 Europe and America. Both have a phylogenetically ancient character. 

 Catinella has a Pacific center and is represented by different subgenera in 

 North America and northwestern Europe respectively. Coilostele occurs 

 within a series of seemingly isolated areas from southernmost Spain to 

 Timor; in addition there is, according to Pilsbry (1948, p. 1051), a quite 

 isolated occurrence in Mexico. 



The distribution of these genera exhibits a pattern so decidedly relic that it 

 seems hardly possible to discuss them in connection with any specific alterna- 

 tive of dispersal. 



THE RECENT RELATIONS OF THE LAND GASTROPOD FAUNA 

 IN THE NORTH ATLANTIC REGION 



From Figs. 1 and 2 it is obvious that the Pleistocene caused no major 

 changes in the composition of the gastropod fauna, neither in North America, 

 nor in Europe. There occurred no mass extinction of species or radical 

 dislocations of the gastropod faunas during the Glacials. Evidently the local 

 Tertiary faunas largely survived within, or in relative proximity of the recent 

 areas. The idea of radical changes in the distribution of the biotas during the 

 Pleistocene, advocated especially by Deevey (1949), has a very moderate 

 bearing for the terrestrial Gastropoda. However, in the North Atlantic 

 region, in a narrow sense, their distributional pattern has been formed in the 

 Quaternary, perhaps throughout in the Post-glacial time. 



Figure 3 illustrates the distribution of the gastropod species in the area. 

 Excluded from the material are all settlements due to anthropochorous 

 dispersal. Sometimes the origin is difficult to determine, and in such instances 

 the occurrence within the territory in question has been indicated by hatching. 

 The diagram is based on information given by Brooks and Brooks (1940), 

 Ellis (1951), Forcart (1955), Lohmander (1938), Mandahl-Barth (1938), 

 Oekland (1925), and Pilsbry (1939-48), in addition to which unpublished 

 material in Scandinavian and American museums has been considered. 



The material has been divided into four categories, viz. endemic European, 

 endemic American, and Holarctic species, plus representatives of the Holarctic 

 form complexes, which seem to be specifically distinct on the two sides of the 

 Atlantic. It may be admitted that our present knowledge does not always 

 allow us to draw a sharp border between the last two categories. Furthermore, 

 the question as to whether the genetic connection is continuous within the 

 Euro-Siberian territory is left open. Endemic representatives for Holarctic 

 genera are assigned to the European and the American groups respectively. 



