COLORATION OF LAND SNAILS. 191 



the most troublesome of these, if we may judge by the elaborate 

 means which have been evolved for protection against them. 

 Beetles, especially those of the family Carabidcs, are not outdone 

 by a Provencal vintner in their appreciation of a toothsome 

 Helix; and it is interesting to watch the celerity with which 

 a beetle of the genus Cychrus or Dicczlas eats a snail out of his 

 shell. 



Various organs have been modified or developed to prevent 

 intruders from entering the aperture of the shell. In one 

 group of land snails there is a calcareous plate, called the oper- 

 culum, secreted upon the upper surface of 

 the fleshy foot of the animal. This plate is 

 the last part to enter the shell when the ani- 

 mal retracts itself, and it fits closely into the 

 aperture, closing it like a valve or door. Ex- 

 amples of this structure are seen in the com- 

 mon Helicinas of America and the genus 

 Cyclostoma of Europe. Fl0 . 5 .-Atopa achate. 



The majority of air-breathing snails, how- Broken, to show the nar- 



j» -1 n • n i> rowness of the passage 



ever, are far removed genealogically from between the foidi. 

 the operculum-bearing group, belonging, in- 

 deed, to quite a different phylum in which the operculum has 

 never been developed. Failing this, a completely different struct- 

 ure has been adapted to the same use. From the rim or lip 

 around the aperture spring processes of the shell substance, pro- 

 jected into the opening of the shell and decidedly narrowing it. 

 An example of this structure in its primitive form is seen in the 

 three-toothed snail, Helix tridentata, and its allies. The project- 

 ing "teeth/' as these processes are called (although they have 

 nothing to do with the true mouth of the animal), are prominent 

 enough to exclude the larger beetles, and insects sufficiently small 

 to be admitted would be drowned in the viscid mucus or slime 

 freely exuded by the snail. 



More complex is the obstructing mechanism in many of the 

 snails of the Southern States and of South America. In some 

 species — the Caracolus labyrinthus of Panama, for example — one 

 wonders how the snail himself can get in or out of his own shell, 

 so tortuous is the passage. These Southern forms represent the 

 highest development of the three-toothed type of aperture. The 

 meaning of this increasing complexity appears, when we remem- 

 ber that the regions where the most complicated types of snails 

 are found are known to be practically coincident with the regions 

 producing carnivorous Coleoptera in the greatest numbers and 

 the most exuberant variety of forms. The writer once confined 

 in a box with carnivorous beetles a number of snails with 

 strongly " toothed " apertures (Helix uvidifera) and a number hav- 



