24 A MANUAL OF AMERICAN LAND SHELLS. 



Several of the above will eventually prove to be synoiiyiiies, but tlie 

 .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 pecul- 

 iarly 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 have 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 i^eculiar Pacific forms, such 

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

 otliev hand, the only form which has any development in the Central 

 Province, Patula, is scarcely known in the Pacific Province. 



Compared with Eastern North America, or the Eastern Province, 

 as it is designated below, the Pacific Province is remarkable for the 

 al iseuce of all the larger Zonites. The presence of the smaller species also 

 may i)erhaps be accounted for by migration from the north, so that the 

 genus Zonites cannot be considered as characteristic of the province. 

 The genus Pupa is less common. Tebeimophorus, so universally distrib- 

 uted in Eastern North America, is unknown, and so are the southern 

 genera Glandina and Bulimulus. On the other hand, we find the genus 

 MacrocycUs much more developed, and meet several genera unknown 

 in the Eastern Province, such as Ariolimax, Binnei/a, Prophysaon^ and 

 Eiinphillia. The genera of disintegrated Helix are proportionally more 

 developed in the Pacific Eegion, and are represented by quite dis- 

 similar subgenera. The genera so peculiar to the Eastern Province, 

 Polygyra, IStenotrema, Triodopsis, Mesodon, are scarcely represented. 

 In their place we find Aglaia and Arionta, forms unknown in the Eastern 

 Province. The latter, though feebly represented in Europe, is character- 



* Since the above was published I have received living specimens of Potula solitaria 

 from tlie Dulles on the Columbia River, proving that that species has passed the bar- 

 rier of the Cascade Mouutaiua and penetrated into the Pacific Region. It had al- 

 ready been noticed in the Central Province. 



