18 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



The boundaries of these provinces and the subdivisions which appear 

 to exist in them will be given below, as well as lists of their peculiar 

 species. It must be distinctly understood, however, that future re- 

 searches, especially at the South and Southwest, may greatly modify 

 the views here presented. 



I. The Pacific Province 1 comprises a narrow strip between the 

 Sierra Nevada and Cascade Mountains on the east, and the Pacific 

 Ocean on the west. Its southern limit is San Diego, from whence it 

 extends northerly into Alaska. 



Over the whole of this province the following species range : — 



Macrocyclis Vancouverensis. Ariolimax Columbianus. 



sportella. Prophysaon Hemphilli. 



Mesodon Columbiana. Succinea rusticana. 



germana. Oregonensis. 



Arionta tudiculata. Nuttalliana. 



Over the whole of this province we find also the following species com- 

 mon to Eastern North America. They also extend over the whole north- 

 ern portion of the continent, where the mountains by their lower altitude 

 are not barriers to distribution. It is, no doubt, from these regions that 

 they have spread through the Pacific Province, and not westward over 

 the Rocky Mountains. Had other Eastern species extended over the 

 boreal regions, we should, no doubt, have found them also spreading 

 into the Pacific States. They are especially found along the Sierra 

 Nevada. 



Zonites arboreus. Limax campestris ? 



indentatus. Patula striatella. 



minusculus. Helicodiscus lineatus. 



milium. Punctum minutissimum. 



In the Pacific Province we also find several species common to the 

 circum polar regions of Asia, Europe, and America. They have like- 

 wise spread southward along the Sierra Nevada and on either side of it. 



Thus his Californian and Rocky Mountain Sub-Region are identical with my Facific 

 and Central Provinces. His Canadian Sub-Region is about the same as my Northern Re- 

 gion of the Eastern Province. His Alleghany Sub-Region includes both my Interior and 

 Southern Region of the Eastern Province. 



1 A most interesting account of this fauna is given by Dr. J..G. Cooper : "On the 

 Distribution and Localities of West Coast Helicoid Land Shells" (Am. Journ. of Conch. 

 II. p. 211, with a map). 



