OO THE NAUTILUS. 



three years, and is given as a basis for work, with the hope that 

 others may add to it. The species are all from the western side of 

 the range, or Pacific slope, with the exception of a few, which are 

 properly indicated where they are discussed. 



Missoula is located in a valley in which the Hell Gate and Bitter 

 Root rivers unite to form the Missoula river. West of the Bitter 

 Root river the Bitter Root range of mountains extend parallel with 

 the river in a northerly and southerly direction. So far the writer 

 has explored but a few spots in these mountains and along the rivers. 

 But the results have been surprisingly good. North of the valley 

 lies the Cabinet range, rugged and broken. Few spots in this have 

 been examined. Across the Cabinet range lies the Flathead Indian 

 Reservation. The crest ol the Mission range marks the eastern 

 border of the reserve. The Mission range extends almost due north 

 and south for a distance of nearly a hundred miles. The southern 

 end contains the highest peaks, reaching 10,000 feet, while the 

 northern end slopes down to the Swan river, and has been ground 

 smooth by glacial action. 



Out of the Mission range four large creeks flow across the Mission 

 valley, joining each other or the Pend d'Oreille river, which is the 

 outlet of Flathead lake. The range makes the eastern bank of Flat- 

 head lake for its entire length. In the canons of this range numer- 

 ous small lakes lie nestled among the hills, invisible until one comes 

 suddenly to the bank. Sin-yale-a-min lake is at the base of Sin- 

 yale-a-min peak, at the southern end of the range. A ten days' 

 camp at this lake brought to light probably all the shell fauna to be 

 found. To the north the mountain produced the very interesting 

 variety of Pyramidula strigosa described later. 



McDonald lake is 15 miles north of Sin-yale-a-min lake, 500 feet 

 lower in altitude, at the base of McDonald peak. Ten days at this 

 spot produced several quarts of P. elrodi Pils., besides the first living 

 shells. Another camp at Crow creek produced several valley shells. 

 Several camps at different points on Flathead lake produced other 

 species from the sands and from the water. Swan lake is on the 

 eastern side of the Mission range. A camp on this lake added one 

 to the list in the western part of the State, not found elsewhere. 



"While the collecting represented by these notes has extended 

 through four summers, the results will probably be modified when a 

 further study of the extensive country has been made. 



