3o8 CHAPTER III 



between highly disjunct present areas of old taxonomical groups. The primitive 

 beetle family Cupedidae (fig. 60) is a good example. 



As -more and more recent species appear from the course of the Tertiary, the 

 geographical character of the different faunas and floras becomes more easy to 

 fix; and elements, often identified to species, of an indisputable "American" 

 type— judged from present distribution— were discovered in Europe. 



The Tertiary development of the European fauna of terrestrial and limnic 

 Molluscs is notably well known and has been summarized by Ehrmann (1914). 

 From the Eocene no recent species is known; the connections, according to present 

 distribution of genera or groups, were largely towards the Tropics, including, 

 but not favouring. South and Central America. Of particular interest is the family 

 Oleacinidae (p. 283), now restricted to tropical America, subtropical North America 

 and the Mediterranean, but found as fossil in Europe as early as in Upper Creta- 

 ceous. 



In the OUgocene more decidedly American types appear, among these genus 

 Strobilops {Strobilus auctt.), now chiefly American but also occurring in East 

 Asia (fig. 61). It persisted in Europe at least to Middle Pliocene. Pilsbry (1948, 

 p. 853) assumes an Asiatic centre of origin for Strobilops, with subsequent radia- 

 tion, west into Europe, east across the Bering bridge into America. 



Other Oligocene Molluscs also show relationship with America, for instance 

 several freshwater Bivalves. Modell (1943) therefore postulates a direct Trans- 

 atlantic land-connection in this period, which was probably of "Wegenerian" type. 

 Yet the so-called American forms of Oligocene Molluscs in Europe are constantly 

 associated with other extra-European elements, mainly with recent occurrence in 

 Asia. 



In the Miocene and Pliocene periods genera and species groups suggesting Ameri- 

 can and South or East Asian connections gradually and contemporaneously 

 disappear. The Upper Pliocene contains an almost entirely European fauna and 

 no "American" Molluscs; nor are any known from the Pleistocene. 



A most interesting light has quite recently been thrown upon the late Tertiary 

 and early Pleistocene history of the European flora through the intense investiga- 

 tions in Polonia by Szafer (1954). In Lower Pliocene the American element was 

 twice— but the East Asian four times (!)— as numerous in species as the generally 

 Eurasian group. The balance changed gradually in favour of Eurasian plants but 

 not until the first Pleistocene glaciation (Giinz) did this element take a clearly 

 dominating position. In the first part of the following Interglacial period the East 

 Asian group was well represented (11 species) but it disappeared completely 

 during the course of this period, whereas two species {Tsuga sp. and Osmunda 



