GEOGRAPHICAL DISTRIBUTION. 27 



Pupa borealis. Succinea Haydeni. 

 Vertigo Gouldi. Verrilli. 



Boliesiana. Higginsi. 



simplex. Groenlandica. 



Punctum minutissimum. 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 across 

 America. In their progress southward, also, they have met with no 

 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. 1 Such are : — 



Zonites viridulus. Vallonia pulchella. 



fulvus. Ferussacia subcylindrica. 



nitidus. Pupa muscorum. 

 Acanthinula harpa. 



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

 freys 2 is correct in referring the following American species to those 

 of Europe : Vitrina limpida = V. pellucida, Punctum minutissimum = 

 Helix pygmsea, Drap., Limax campestris = L. lsevis, Mull., Vertigo 

 Gouldii=:V. alpestris, Aid., Vertigo Boliesiana = V. pygmsea, Drap., 

 V. ovata = V. antivergo, Drap., V. ventricosa = V. Moulinsiana, V. 

 simplex = V. edentula, Drap., Succinea ovalis = S. elegans, Risso, S. 

 Totteniana = S. putris, Drap. var. A comparison of the lingual denti- 

 tion of many of these has convinced me that Mr. Gwyn Jeffreys is not 

 correct, as shown below in the descriptive portion of my work, under 

 each species of the list. 



From Asia have come into Alaska the following : Vitrina exilis, Patula 

 patqier, Pupa borealis. 



1 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-barriers, but 

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



Zonites arboreus. Limax campestris. 



indentatus. Patula striatella. 



minusculus. Helicodiscus lineatus. 



milium. Punctum minutissimum. 



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

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

 here. 



» Ann. and Mag. N. H., 1872, 245, 246. 



