88 



MANUAL OF THE MOLLUSCA. 



few in the extromo north), and each possessing many charao- 

 teristic genera. 



The Land Provinces represented on the map are the principal 

 Botanical Eegions of Prof. SchouW, as given in the Physical 

 Atlas of Berghaus ; and it is proposed to inquire how far these 

 divisions are confirmed by the land and fresh-water shells, more 

 especially by the land- snails {ITelicidce, Limactdce, and Cyclosto^ 

 midoe), which have been so elaborately catalogued by Dr. L. 

 Pfeiffer.* 



The first Botanical region— that of Saxifrages and Mosses — 

 has not been numbered on the map, although its boundary is 

 given by the line of northern limit of trees. This line nearly 

 coincides with the Isotherm of 32", or permanent ground-frost; 

 but in Siberia the pine-forests extend 15° farther, owing to the 

 absence of winter rains and the bright clear air. 



In this region shells are very rare ; Dr. Middendorff found 

 Physa hypnoram in Arctic Siberia, and Limncea geisericola (Beck) 

 inhabits the warm springs of Iceland. The few species dis- 

 covered by Miiller in Greenland are supposed to be peculiar : — 



Helix Fabricii. 

 Pupa Hoppii. 

 Vitrina angelicse. 



Succinea Graenlandica. 

 Limmsea Vahlii. 

 „ Pingelii. 



LimtiEea Holbollii. 

 Planorbis arcticus. 

 Cyclas Steenbuchii. 



* The distribution of the Ci/cladidce is taken from the British Museum Catalogue, 

 by M. Deshayes. 



