II UNDERGROUND AND ROCK-BORING SNAILS 49 



habitually from 1 to 3 feet below ground, appearing to prefer 

 the vicinity of graveyards. Testacella^ the carnivorous slug, 

 scarcely ever appears on the surface during the day, except 

 when driven by excessive rain, and even then it lurks awhile 

 under some protecting cover of leafage. There is a curious 

 little Helix (tristis Pfr.), peculiar to Corsica, which is of dis- 

 tinctly subterranean habits. It lives in drifted sand above high- 

 water mark, always at the roots of G-eiiista Saltzmanni^ at a 

 depth which varies with the temperature and dryness of the 

 air. In hot and very dry weather it buries itself nearly 2 feet 

 below the surface, only coming up during rain, and burying 

 itself again immediately the rain is over. Like a Solen^ it often 

 has a hole above its burrow, by which it communicates with the 

 air above, so as to avoid being stifled in the sand. The animal, 

 in spite of its dry habitat, is singularly soft and succulent, and 

 exudes a very glutinous mucus. It probably descends in its 

 burrow until it arrives at the humid stratum, the persistence of 

 which is due to the capillarity of the sand.^ I am assured by 

 Mr. E. L. Layard that precisely similar underground habits are 

 characteristic of Coeliaxis Layardi^ which lives exclusively in 

 sand at the roots of scrub and coarse grass at East London. 



Rock-boring Snails. — Cases have sometimes been recorded, 

 from which it would appear that certain species of snails possess 

 the power of excavating holes in rocks to serve as hiding-places. 

 At Les Bois des Roches, ten miles from Boulogne, occur a 

 number of solid calcareous rocks scattered about in the wood. 

 The sides of the rocks which face N.E. and E. are covered with 

 multitudes of funnel-shaped holes, IJ inch in diameter at the 

 opening and contracting suddenly within to \ inch. Sometimes 

 the holes are 6 inches deep, and terminate, after considerable 

 windings, in a cup-shaped cavity. Helix hortensis inhabits these 

 holes, and has been observed to excavate them at the rate of 

 \ inch each hibernation, choosing always the side of the rock 

 which is sheltered from the prevailing rains. It does not form 

 an epiphragm, but protrudes part of its body against the rock. 

 That the snails secrete an acid which acts as a solvent seems 

 probable from the fact that red litmus paper, on being applied to 

 the place where the foot has been, becomes stained with violet.^ 



1 Lecoq, Journ. de Conch, ii. p. 146. 



2 Bouchard-Chantereaux, Ann. Sci. Nat. Zool. (4) xvi. (1861) p. 197. 



VOL. Ill E 



