A MANUAL OF AMERICAN LAND SHELLS. 27 



The following are the species of the Northern Eegion : 



Vitrina limpida. Vallonia pulchella. 



Angelica,. Ferussacda suhcylindrica. 



exilis. Pupa muscorum. 



Zonites fulvns. Blandi. 



nitidus. Soppii. 



viridulus. decora. 



Fahricii. horealis. 



milium. Vertigo Gouldi. 



Binneyanus. Bollesiana. 



fcrreus. simplex, 



exiguus. Micropliysa minutissima. 



miiUidentatus. Suceinea Haydeni. 



Patula striatella. Verrilli. 



asteriscus. Migginsi. 



pauper. Groenlandica. 



AcantMnula liarpa. Totteniana. 



Of the above, several are circumpolar species, common to the three 

 continents of Europe, Asia, and America. There being no mountain 

 barriers in these regions, they are not restricted in their range acros 

 America. In their progress southward also they have met with n 

 transverse mountain barriers, but have spread equally on the east and 

 west of the Rocky Mountains and Sierra Nevada. Hence we find them 

 common to the whole of North America.* Such are — 



Zonites viridulus. Vallonia pulchella. 



fulvus. Ferussacia suhcylindrica. 



nitidus. Pupa muscorum. 

 AcantMnula liarpa. 



This list will be increased should it be proved that Mr. Gwyn Jef- 

 freys! is correct in referring the following American species to those 



* In the same way we can account for the distribution of the small eastern species 

 over the Central and Pacific Provinces. They have not crossed the mountain barri(.M| 

 but spread southward from their wider range in the north. Such are — 



Zonites arhoreus. Umax campestris. i 



indentatus. Patula striatella. I 



mintisculus. Melicodiscus lineatus. 



milium. Micropliysa minutimma. 



These northern species, both indigenous and circumpolar, may have becu assisted 

 in their migration southward by glacial agencies. There is a wide field for specula- 

 tion here. 

 tAnn. and Mag. N. H., 1872, 245, 246. 



