22 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Patula striatella. Arionta sequoicola. 

 Microphysa Lansingi. Diabloeiiais. 



Helicodiscus liiieatiis. Traski. 



Gonostoma Yatesi. Dupetithouarsi. 



Triodopsis Hai f ordiana. ruficincta. 



loricata. facta. 



Mesodon Columbiana. Gabbi. 



geriuana. Kelletti. 



devia. Stearnsiana. 



Aglaja fidelis. Euparypha Tryoni. 



infumata. Glyptostonia Newberryanum. 



Hillebrandi. Ferussacia subcylindrica. 



Arionta arroaa. Pupa Rowelli. 



Tow^nsendiana. Californica, 



tudiculata. corpulenta. 



Nickliniana. Succiuea Sillimani. 

 Ayresiana. Stretchiana. 



redimita. Hawkinsi. 



intercisa. rusticana. 



exarata. Nuttalliana. 



ramentosa. Oregon ensis. 



Californiensis. Punctum minutissimum. 



Carpenteri. Veronicella olivacea. 

 Mormonum. 



Several of the above will eventually prove to be synonymes, but the 

 total number of species is small in comparison with the great size of the 

 Pacific Province. An equal extent of territory in the Mississippi Valley, 

 or even on the Atlantic coast, would show a larger number ; and the 

 comparatively small regions of Texas, Florida, and the Cumberland 

 Mountains would each show an equal number of species peculiar to 

 itself, independent of what they have in common with the rest of East- 

 ern North America. This disparity in number is still more plainly 

 shown in the separate region of Oregon. Thus it appears that the 

 Pacific Province is not rich in the number of its species, but it is 

 peculiarly favored in their size and beauty, — in this respect strikingly 

 in contrast with the Central Province and Eastern Province. 



From the Central Province the Pacific Province is quite distinct. A 

 few species liave been shown above to inhabit both slopes of the Sierra 

 Nevada, and a few of the Oregon species have passed the barrier of the 

 Cascade Mountains on the north,^ but the peculiar Pacific forms, such 

 as Arionta and Aglaia^ are unknown in the Central Province. On the 



1 Since the above was published I have received living specimens of Patula solitaria 

 from the Dalles on the Columbia River, proving that thft species has passed the barrier of 

 the Cascade Mountains and penetrated into the Pacific Region. It had already been 

 noticed in the Central Province. 



