DEAN : NOTES ON SCANDINAVIAN MOLLUSCAN FAUNA. 357 



for both islands, Gothland and Oland, and has probably extended its 

 range, though not so far, by a similar route. Mr. Stelfox says of this 

 species that in Norway it is quite common in districts composed of 

 granite and schist. Whether there were present the requisite con- 

 ditions for dispersal in the case of a species like Helix pomatia L. it 

 is difficult to say ; its position in Eastern Sweden has been up to the 

 present ascribed to artificial introduction. 



The geological formation in the Island of Gothland is Silurian 

 limestone, the beds nearly horizontal, but with development of steep 

 cliffs on the western coast. A similar Silurian formation occurs on 

 the opposite, Russian side of the Baltic ! In many parts there is an 

 absence of overlying glacial drift, leaving the limestone exposed and 

 giving the characteristic conditions of the " limestone pavement." A 

 few of the plants do not occur on the Swedish mainland, though the 

 flora is closely related to the flora of Oland and to the flora of the 

 Russian provinces on the other side of the Baltic.^ Gothland, like the 

 mainland of Sweden, is a typical forest region. The historical deve- 

 lopment of the flora of Gothland has been studied by Sernander. 

 In the "Littorina age" of post-glacial time, there was an extension of 

 the sea in many parts of West Europe. The Baltic had probably 

 been hitherto a fresh-water lake (" the Ancillus {sic) Sea,") but now 

 became more extensive. The lower layers of peat in Gothland date 

 from these Ancillus or Littorina periods (named after the character- 

 istic molluscs) ; they contain a large number of plants, Phragiiiites 

 being abundant. It is likely that the Littorina subsidence came 

 about the end of the Neolithic period. At the present day there are 

 two species of fresh-water shells with an eastern distribution — Neri- 

 tina fluviatilis L. and Planorbis corneas L. — which, with Helix 

 pomatia L., characterize the Stockholm area. 



The northern boundary of Sweden is determined partly by the 

 Tornea Elf and partly by the Muanio Elf ; the Tornea Lappmark 

 being in Finland and the Lulea Lappmark in Sweden. This remote 

 land has one of the smallest faunas in the world. The village of 

 Karesuando is the most northern in Sweden, and on the Muanio Elf 

 Muonioniska is a few miles further down the river. The region was, 

 as I have said, visited by Linnseus early in the eighteenth century, or 

 exactly i8o years ago. The following species were collected by Herr 

 Christiernensen on the Russian or Finland side near the above 

 localities, which places may be taken roughly as lying about 200 

 miles within the Arctic Circle. From Muonioniska, visited in 1879, 



I " The Vegetation of Gothland," by H. Hamshaw Thomas. 



