THE STORY OF THE LAND SNAILS 337 



and extend almost to the center of the opening, so 

 that there are only narrow fissures left between 

 them, while the sharp-edged lamellae are almost 

 as much convoluted as the lobes of a brain. It 

 is interesting to watch one of these creatures 

 emerging to crawl, for it seems actually to flow out 

 of the aperture as if it were composed of very 

 thick syrup. The teeth and lamellas make deep 

 impressions in the body as it moves out past 

 them, but after getting by the constricted aper- 

 ture the snail's body immediately resumes its 

 proper rounded form. 



That this armature is developed to prevent 

 beetles from entering and devouring the animal 

 seems well proven. Pilsbry has shown this by the 

 evidence furnished by two groups of land snails of 

 the genus Pleurodonte which inhabit the Andean 

 region of South America. One of these groups 

 called Labyrinthus, on account of the remarkable 

 development of teeth and lamellae in its aperture 

 inhabits the hot lowlands of this area, where car- 

 nivorous beetles are abundant. The other and 

 nearly related group (Isomeria) of the same genus 

 is found only on the mountains where beetles are 

 few. Their shells have only rudimentary teeth 



