MOLLUSCA 



133 



The land snails so far discussed have the form called helicoid, 

 that is, with a more or less flattened spiral. Another type of 

 shell has been called pupoid or pupilloid, the shape being that of 

 a small cylinder, or barrel, or spindle. A very common member 

 of this series, 5 or 6 mm. long, with shining surface and rounded 

 contours, is Cochlicopa lubrica. The very same species is abun- 

 dant as far away as England, and I have found it in Siberia. Its 

 numerous relatives belong to the European region and along the 

 Mediterranean; there are many species in the Madeira Islands. 

 Just how this snail has managed to travel so far, and keep its 

 characters unchanged, is a mystery. Curiously enough, it is 

 much less variable in Colorado than in England, whence nine 

 named varieties have been recorded. Other pupilloid snails are 

 very small, and difficult to identify without a microscope or very 

 good lens. The commonest ones belong to the genera Papilla 

 and Vertigo, and are boreal types. 



Vertigo ovata 



Say 

 (Much enlarged) 



Vertigo 



concinnula 



Ckll. 



(Much 



enlarged) 



Helicodiscus parallelus Say 

 (Much enlarged) 



Gastrocopta armifera 

 Say (Greatly enlarged) 



The amber snails, Succinea, are more or less fusiform, with 

 a pointed spire, and the suboval aperture so large that it is more 

 than half the length of the shell. We have several species in 

 Colorado, and the genus is widely distributed over the world, 

 especially on remote islands. 



Succinea haydeni Binney 



Succinea a vara Say 



