THE LAND GASTROPODA IN THE NORTH ATLANTIC REGION 

 Table 1 



157 



* In the Archeo- and Holotropical group, marine littoral genera play a major role. 

 This refers to four extinct and six recent genera. They are useful as climate-dependent 

 indicators in faunal development, but do not tell much about the ways of dispersal of the 

 land fauna proper. Apparently, their often very wide distribution is a consequence of the 

 fact that they are far better adapted to the possibilities of passive dispersal offered, e.g 

 by ocean currents, than the other, truly terrestrial genera. In fact, some littoral species are 

 rather amphibious than terrestrial. Two of the strictly terrestrial genera are regarded here 

 as Archeotropical, viz. Pseiidocohimna and Protornatellina, Paleocene and Cretaceous 

 respectively. To the Holotropical group are assigned Pupoides, Piipisoma, Cecilioides, 

 Lamellaxis and Opeas. Of these, Pupoides appears in the Eocene, the others in N. America, 

 are known from the Holocene only. 



t In the North American-East Asiatic group the record of Rhiostoma, from Oregon 

 Miocene, must be regarded as somewhat problematic. Calinella, with a Pacific center, has 

 been included in this group. The remaining genera are Hendersonia, Strobilops and Gastro- 

 copta. The last two have a wider distribution and a complicated history, briefly discussed in 

 the text. 



+ Some of the endemic North American genera show significant extra-continental 

 relations. Philomyciis, Anadenuhis and Prophysaon have their closest relatives in East or 

 Central Asia. Concerning the relations to certain European genera of Gastrodonta and 

 Euglandma (the latter assigned to the Central and South American group), see text. 



Cf. also the caption to Fig. 1. 



and the Old World to distinct species and subgenera. Apparently their 

 dispersal must have proceeded during a very long time, a statement which is 

 verified by paleontological evidence. A remarkable feature in the distribution 

 of the Holarctic genera is their dominance in the gastropod fauna north of 

 47° N. Lat., thus largely within the area of the Pleistocene glaciations. 



However, not only in the Holarctic element, but also in the Tropical and 

 East Asiatic, affinities to Europe are evident. These are partly of a highly 

 intricate nature. But before the routes of dispersal can be discussed, the 

 European gastropod fauna and its history must be regarded. 



THE EUROPEAN LAND GASTROPOD FAUNA AND ITS 

 DEVELOPMENT 



The history of the European land gastropod fauna shows a pattern which 

 is very different from that of the North American. In detail it is much more 



