2 4 HABITS OF LAND MOLLUSCA chap. 



North Siberia, in 73"^ 30' N. lat., a region whose mean annual 

 temperature is below lO"" 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. Paludina 

 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. glacialis 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 Hyaliniae 

 are very hardy. Arion, in spite of having no external shell to 

 protect it, is apparently less affected by the cold than Hdio:, and 

 does not commence hibernation till a later period in the autumn. 

 The operculate land Mollusca, in spite of the protection wliich 

 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 Helieina which inhabits the southern States of North 

 America has been known to be almost exterminated 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 Buliminus (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. Norcl, Abbeville, 1840, p. 150. 



- Joly, Comptes Reiidus, 1842, p. 460 ; compare W. A. Gain, Science Gossip, 

 xxvii. p. 118. ^ Von Martens, SB. Nat. Fr. Berl. 1881, p. 34. 



