32 



TERRESTRIAL AIR-BREATHING MOLLUSKS. 



before the Rocky Mountains are reached, the western boundary of the 

 Interior Region. But one species, Patula solitaria, seems to have 

 passed this mountain-barrier into the Central Province. This is found 

 with P. Cooperi in Montana and Idaho, very difficult to distinguish 

 from forms of the last species. It is, however, oviparous (from Salmon 

 River, Idaho), while P. strigosa, Cooperi, Hemphilli, and Idahoensis are 

 viviparous. 1 It has also passed into the Pacific Province at the Dalles. 

 The following list contains the names of all the species inhabiting the 

 Interior Region, including those which have spread into it from the 

 Northern Region : 



Macrocyclis concava. 

 Zonites fuliginosus. 

 friabilis. 

 laevigatus 

 ligerus. 

 intertextus. 

 inornatus. 

 nitidus. 

 arboreus. 

 viridulus. 

 indentatus. 

 limatulus. 

 minusculus. 

 fulvus. 

 gularis. 

 suppressus. 

 interims. 



Limax campestris. 

 Patula solitaria. 

 alternata. 

 perspective 

 striatella. 



Helicodiscus lineatus. 

 Strobila labyriuthica. 

 Polygyra Dorfeuilliana. 

 leporina. 

 auriformis. 



Stenotrema stenotremum. 

 hirsutum. 

 monodon. 

 Triodopsis palliata. 

 obstricta. 

 appressa. 

 inflecta. 

 tridentata. 



Triodopsis fallax. 

 Mesodon albolabris. 



multilineata. 

 Pennsylvanica. 

 Mitchelliana. 

 elevata. 

 exoleta. 

 dentifera. 

 thyroides. 

 clausa. 

 profunda. 

 Sayii. 



Acanthinula harpa. 

 Vallonia pulchella. 

 Pupa muscorum. 

 pentodon. 

 fallax. 

 armifera. 

 contracta. 

 rupicola. 

 corticaria. 

 Vertigo milium. 



ovata. 

 Succinea retusa. 



Grosvenori. 

 Mooresiana. 

 ovalis. 

 lineata. 

 avara. 

 aurea. 

 obliqua. 

 Totteniana. 



Tebennophorus Caroliniensis, 

 Pallifera dorsalis. 



1 It has been suggested by Dr. H. Dohrn that this characteristic is connected with the 

 fact of the great dryness of the soil in the Central Province. The youug shell is ready to 



