96 



GEOI^OGY OF LA SALLE COUNTY. 



we have one variegated species, H. alternately and 

 three banded species, noticed hereafter. In tropical 

 climates the shells are brilliantly colored, a fact that 

 applies to marine forms as well. 



One peculiarity of our snails is the tooth-like 

 appendag-e found in the apperture of many of the spe- 

 cies. These have been grouped as Helicodonta by 

 Ferussac. The snails, having passed their summer 

 existence, prepare, on the approach of cold weather, to 

 go into winter quarters. These they find in the same 

 localities where they have lived. They either burrow 

 in the g-round or attach themselves to the under side of 

 their shelter. Having- disposed themselves with the 

 aperture of the shell upwards, they blov^^ forth a 

 mucous-like secretion from the collar. This is ejected 

 so as to cover the aperture of the shell. We call this 

 the efi^hrag-m. It hardens and eifectually shuts out 

 the cold. As the season advances, the animal retiring 

 further within builds more of these barricades in the 

 same manner as the first. Finally, the pulsations of 

 the heart becoming slower and slower, at last ceases 

 entirely. The sleep is complete. They are eaten in 

 some parts of Europe — Paris and Vienna. 



