THE SNAILS OF GEEENLAND 21 



ninety-one in Iceland.* Of tihe more hardy spiders the per- 

 centage of survival is very different, for there are fifty-three 

 species in Greenland and only twenty-four in Iceland.f 



The theory of the survival of species in Greenland may 

 be tested by some other examples. Besides Helix hor- 

 tensis about a dozen other kinds of land and fresh- 

 water mollusks inhabit the country.:j: Eight of these either 

 have their centre of distribution in Greenland or are 

 quite peculiar to the country. These are Planorbis nathorsti, 

 P. arcticus, Limnaea vahli, L. holbolli, Succinea groen- 

 landica, Vitrina angelicae, Conulus fabricii and Pupa hoppii. 

 The two species of Planorbis are also known from Labrador ; 

 Succinea groenlandica occurs in Iceland ; P. arcticus has 

 been met with in Scandinavia, Finland and Siberia. The 

 first of the Limnaeas ranges from Greenland to Alaska, 

 the other is peculiar to Greenland. The latter, however, 

 is replaced in boreal North America by the closely-allied 

 Limnaea retusa. Vitrina angelicae is not found in America, 

 but occurs in Iceland and Norway. Conulus fabricii is pro- 

 bably only a variety of the common Conulus fulvus of northern 

 Europe, Asia and America, while Pupa hoppii is confined to 

 Greenland. With the single exception of Planorbis arcticus 

 all these species live at present well within the glaciated area, 

 that is to say, within that portion of the northern regions 

 supposed to have been either wholly or partially buried by 

 ice during the Glacial Epoch. As none but Planorbis arcticus 

 have ever been found fossil outside that area, we may assume 

 with some justification that most of them originated in Green- 

 land, and that all, at any rate, survived the Ice Age in that 

 country. Planorbis arcticus, as Mr. Kennard § informs me, 

 has been taken in Pleistocene deposits in Denmark and in 

 the south of England. (Compare also Kennard and Wood- 

 ward's paper.) 



It is more difficult to demonstrate that butterflies and moths 



* Poppius, B., " Ooleopteren des Arktisclien Gebietes," p. 428. 

 t Strand, E., " Arktische Araneae," p. 436. 



X Mdrcli, O. A. L., " Land and Freshwater Mollusca of Greenland." 

 § Kennard, A. S., and B. B. Woodward, " Extinct post-pliocene 

 Mollusca of Southern England," p. 5. 



