170 HENRIK W. WALDEN 



excluded that forthcoming faunistic and taxonomical research will unveil 

 some further examples within the Holarctic genera, but it will scarcely change 

 much in the picture. The favorable situation for dispersal, due to the narrow 

 separation of the land masses and the late direct connection, apparently has 

 been of limited importance for the Gastropoda when the ecological conditions, 

 mainly climatic, are preventive. Obviously this has a bearing on the situation 

 in the North Atlantic region too. 



It must be admitted that the discussion which can be carried out from 

 present knowledge concerning the land Gastropoda within the Arctic and 

 northerly Boreal realm is of rather general character. Few positive conclusions 

 are possible. The key to several problems, which also concern the North 

 Atlantic region, may lie within the immense territories in northern Asia and 

 North America from which extremely little is known about the land Gastro- 

 poda (as well as most other animal groups). Data are needed equally concern- 

 ing distributional patterns, taxonomy on ± species level, and fossil occurrence. 

 The fact that the Pleistocene refugia, most firmly supported by geological 

 evidence, existed in the Bering Strait region may be especially considered in 

 this connection. Also, for an understanding of prospective North Atlantic 

 refugia, data from those of the Pacific may be beneficial. 



It is a matter of course that the detailed field research on the first hand 

 must be concentrated on geographical sectors and habitats which are thought 

 to be especially profitable, as well as on species of outstanding significance. 

 But such research can attain its full value only against the background of a 

 fairly homogeneous knowledge about the whole territory, also including the 

 extensive "less interesting" areas. Strictly speaking, no area in which biota 

 exist is uninteresting to the biologist. It depends upon the problem to which 

 the approach refers. 



With the resources of transport available today there are scarcely any 

 technical obstacles to bringing forth an acceptably homogeneous fund of 

 data from the Arctic and northernmost Boreal regions. Thereby it would be 

 possible to adjust a good deal of the obvious imbalance in recent discussions 

 of zoogeography and faunal history. 



REFERENCES 



Baker, F. C. (1920). The life of the Pleistocene or Glacial period. Bull. Univ. III. 17, 41, 



1-476. 

 Brooks, S. T. and Brooks, B. W. (1940). Geographical distribution of the recent Mollusca 



of Newfoundland. Ann. Carneg. Mils. 28, 53, 53-75. 

 Clarke, A. H., and Erskine, J. S. (1961). Pre-Columbian Littovim littoiea in Nova Scotia. 



Science 134, 393-394. 

 Darlington, P. J., Jr. (1957). Zoogeography : the geographical distribution of animals. 



New York. 

 Davies, a. M. (1934). Tertiary Faunas. Vol. II. Guildford. 

 Deevey, E. S., Jr. (1949). Biogeography of the Pleistocene. I. Bull. Geol. Soc. Amer. 60, 9, 



1315-1416. 



