UNDERGROUND AND ROCK-BORING SNAILS 49 



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 distinctly subterranean habits. It lives 

 in drifted sand above high-water mark, always at the roots of 

 Genista Saltzmanni, at a depth which varies with the tempera- 

 ture 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 bmying 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 capil- 

 larity of the sand.^ I am assured by Mr. E. L. Layard that 

 precisely similar underground habits are characteristic of Coeli- 

 axis 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 Eoches, ten miles from Boulogne, occur a 

 number of solid calcareous rocks scattered about in the wood. 

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

 with multitudes of funnel-shaped holes, Ij inch in diameter at 

 the opening and contracting suddenly within to ^ inch. Some- 

 times 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 

 I" 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.^ 



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

 - Boiichar.l-Cliaiitereaux, Ann. Sci. Nat. Zool. (4) xvi. (1861) p. 197. 

 VOL. Ill E 



