LAND REGIONS. 383 



and Cydostomidd), wliich have been so elaborately catalogued by Dr. L. 

 Pfeiffer.* 



The first Botauical 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 per- 

 manent ground-frost; but in Siberia the pine-forests extend 15° further, 

 owing to the. absence of winter rains and the bright clear air. 



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

 rum in Arctic Siberia, and LimncBa geisericola (Beck) inhabits the warm 

 springs of Iceland. The few species discovered by Moller in Greenland are 

 supposed to be peculiar : — 



Helix Fabricii. Succiuea Groenlaudica. Limnasa Holbollii. 



Pupa Hoppii. Limnaea Valilii. Planorbis arctious. 



Vitrina angelieae. „ Pingelii. Cyclas Steenbuchii. 



1. Gekmanic Region. 

 The whole of Northern Europe and Asia, bounded by the Pyrenees, Alps, 

 Carpathians, Caucasus, and Altai, constitutes but one province, with a fauna 

 by no means proportioned in richness to its extent. f 



The land-snails amount to more than 200, but nearly all (or at least five- 

 sixths) are common to the Lusitanian region.fl 



Helix 90 Pupa 44 Cyclostoma 1 



Bulimulus 10 Clausilia 52 Acicula 1 



Zua ^ Vitrina 5 Limax 9 



Azeca I 5 Succinea 5 Arion 4 



Cionella J Balea 1 Carycliium 1 



The fresh-water shells belong to these genera and sub-genera : — 



Lirnnaea 20 Velletia 1 Unio, sp. and vars . . 20 



Ampliipeplea 2 Neritina, vars 3 Anodon, vars 20 



Physa 5 Paludina and Bithynia 23 Alasmodou 3 



Aplex a 1 Valvata 5 Cyclas tt 



Planorbis 16 Couovulus (Alexia) . . 3 Pisidium 11 



Ancylus 7 Dreissena 1 



The British land-shells amount to 74, htsh-vidXtr pulmonifera 24, fresh- 

 water pectinibrancJihita 7, marine pidmonifera 4 ; fresh-water bivalves 15. 

 Of the species formerly thought peculiar, Fupa anglica and Helix fasca have 

 been found in France, and Helix lamellata in Holsace. Helix excavata 

 (Beau) is still unknown l^pon the Continent ; and Geomalactis maculostis and 



* The distribution of the CijcladidcE is taken from the British Museum Catalogue, 

 by M. Deshayes. 



t The mean temperature of the winter and summer months averages 36° — 57°; in 

 Western Europe autumn rain^ prevail, and summer rains in Eastern Europe and 

 Siberia. 



% It was the opinion of Prof. E. Forbes that all the species of the Post -pliocene 

 land of Northern Europe and Asia had originated beyond the bounds of that region. 



