OP CONCHOLOGY. 45 



disappear regularly, according to the climate, towards the north. 

 Thus in the South of Europe Helicogena is represented by H. 

 hortensis, nemoralis, Vindolonensis, sylvatica ; the two last named 

 species disappear in Saxony ; the two first named are found to- 

 gether until the middle of Sweden, where H. nemoralis disappears. 

 H. hortensis is the most northern; it is therefore perhaps not ac- 

 cidentally that it is found in Greenland and Newfoundland. 

 Nearly the same features are to be found in the Hyalinas. 



It is now the question, have the species of the north wandered 

 southward, or were all the species originally southern and wan- 

 dered northward, according to their faculty to endure the cold? 



According to the careful researches of Professor Torell, there 

 are no land and fresh-water shells found in Spitzbergen. 



Spurious Icelandic Species. 

 Nerita fluviatilis. 

 Helix grisea, Dill. 

 Helix pella, L. Rissoa. 

 Helix holiatoidea, L. Velutina. 

 Tellina lacustris, L. 

 " cornea, L. 



are indicated by Schmarda, " Die geographisch Verbreitung der 

 Thiere," y. 378. 



Unio margaritiferus is indicated as found in Iceland by Bory 

 St. Vincent, Diet. Class. 



