24 HABITS OF LAND MOLLUSCA chap. 



temperature is below 10° F. with a range of from 40° F. in July 

 to —30° F. in January. 



It is well known that the Limnaeidae, and probably most 

 fresh-water Mollusca of sub-temperate regions, can continue to 

 live not merely under, but enveloped in ice, and themselves 

 frozen hard. Garnier relates ^ that, during the winter of 1829- 

 30, some large Limnaea auricularia, which had been placed in 

 a small basin, were frozen into a solid mass, experiencing a cold 

 of —2° F. He supposed they were dead, but, to his surprise, 

 when the basin thawed, the Limnaea gradually revived. Palu- 

 dina vivipara and Anodonta anatina have been known to resist 

 a temperature of 23° F., and the former has produced young 

 shortly after being thawed out of the ice.^ As far north as Bodo 

 in Norway (67° 37' N. lat., well within the Arctic circle) there 

 are found no less than fourteen species of terrestrial Mollusca, 

 among them being Balea perversa and Clausilia rugosa.^ 



Vitrina is one of our most hardy molluscs, and may be 

 observed crawling on bright mornings over the frost-covered 

 leaves of a wood or copse. V. glaeialis is said by Charpentier 

 to live in the Alps at a height where the stones are covered with 

 snow from nine to ten months of the year. Many of the Hya- 

 liniae are very hardy. Arion^ in spite of having no external 

 shell to protect it, is apparently less affected by the cold than 

 Helix^ and does not commence hibernation till a later period in 

 the autumn. The operculate land Mollusca, in spite of the pro- 

 tection which their operculum may be supposed to afford, are 

 exceedingly sensitive to cold, and the whole group is without 

 doubt a product of tropical or semi-tropical regions (see map at 

 frontispiece). A species of Helicina which inhabits the southern 

 States of North America has been known to be almost extermi- 

 nated from certain districts by the occurrence of an unusually 

 severe winter. 



One of the highest altitudes at which a land shell is known 

 to live appears to be the Liti Pass (Himalayas, 14,000 ft.). At 

 this enormous altitude, two species of BuUmhius (^arcuatus Hutt. 

 and nivicola Bens.) live on juniper bushes among patches of 

 snow. An Anadenus is said to have been found in a similar 



1 Bull. Soc. Linn. Nord, Abbeville, 1840, p. 150. 



2 Joly, Comptes Bendus., 1842, p. 4G0 ; compare W. A. Gain, Science Gossip, 

 xxvii. p. 118. 3 vou Martens, SB. Nat. Fr. Berl. 1881, p. 34. 



