222 HALF-HOURS IN THE GEEEN LANES. 



its peculiar structure. This consists of an elastic 

 appendage which can be used to close the aperture. 

 If you break off the outer part of the last whorl, 

 you will see a spoon-shaped, shelly plate, attached 

 to the column of the spire by the elastic filament or 

 spring. When the animal creeps out of its shell, 

 this is thrust aside, and when it withdraws, it 

 springs the door to : so we see the principle of 

 having a simple mechanism to close the door when 

 we have passed out of or into a room, was in practice 

 long before man adopted it ! The pupas may be 

 abundantly found in damp moss everywhere, their 

 brown, horny-looking shells being of an elegant 

 shape, but looking as if the stuff had run short 

 before the spire had been completed, so that it had 

 suddenly come to a conclusion. Notwithstanding 

 the apparent insignificance of land snails, they have 

 a wonderful antiquity. Species of pupa have been 

 found fossilised inside the trunks of ancient Car- 

 boniferous club-mosses. They are also abundant, 

 together with fossil bulimi, in the early Tertiary 

 strata of the Isle of Wight and elsewhere. Scarcely 

 less ancient is the family of Helix, for they form 

 beds in the Upper Eocene deposits. As far back as 

 the period of the Norwich and Bed Crags, the same 

 species lived that are still existing in these latitudes. 

 Thus, Helix hispida is a not uncommon fossil in the 

 former deposit, and a comparison with modern forms 

 shows that it has not altered in the meantime. 

 An interesting circumstance occurs with regard to 



