28 BULLETIN OF THE 



Columbia Eiver between the Dalles and Portland, and continues its northerly 

 course on the west side of the Columbia. Numerous spurs, however, break off 

 from the main range, and pass north through East Oregon into Utah and Idaho. 

 One of these spurs, called the Blue Mountains, shoots off the Cascades near 

 Mt. Hood, and runs nearly parallel with the Columbia, forming the eastern 

 boundary of its valley, and is about forty miles from the river, and terminates 

 about abreast of the mouth of Salmon River, Idaho, and on the south side of 

 Snake River. On the north side of Snake River these mountains have local 

 names, but are known by the general name of Bitter Root Mountains. They 

 include Salmon River Mountains, etc. By tracing the course of Snake River 

 and its tributaries you will see it drains the northern part of the great central 

 basin, and when it cut its way through these mountains it very likely drained 

 the great system of lakes that once covered a great part of this central basin. 

 Now the mountain ranges in this portion, northeast, are the metropolis of 

 strigosa so far as we know at present ; and it is not improbable that many indi- 

 viduals, and quite likely whole colonies, of that species are sometimes carried 

 into the streams by rains and floods, and are borne away on the waters towards 

 the Pacific Coast. Occasionally some of the specimens must find or make a 

 lodgement along the banks of the streams, and if the conditions are favorable 

 a colony will spring up and perhaps spread over the neighborhood. The banks 

 of the Columbia between the Dalles and the mouth of Snake River, a distance 

 of one hundred and fifty miles, are destitute of timber, and are covered for sev- 

 eral miles back with loose drifting sand, quite unfavorable to the existence and 

 spread of ]and shells. The locality where I found the variety castaneus was 

 on the bank of the Columbia near Celilo, about fifteen miles above the Dalles, 

 on the east side of the Cascades, but on the west side of the Blue Mountains. 

 This colony must have sprung from specimens brought down the stream by 

 floods. At a subsequent visit it had disappeared. It may be possible some 

 colonies will yet be foxind on the banks of the river below the Cascades. Very 

 likely the original strigosu may have come from some colony planted in this 

 way." 



These same remarks will apply to Patula solitaria, the group of Triodopsis 

 Mullani, and Mesodon ptychophorus. In treating each separate form of the 

 species, I propose to follow the suggestion of Mr. Hemphill, as he has had so 

 much better opportunities than any one else to appreciate their variations. He 

 suggests arranging the group, whether considered as varieties or as distinct spe- 

 cies, in three series according to the modifications of the sculpture of the shells : 

 A. Shell transversely ribbed. B. Shell smooth or with rough striae. C. Shell 

 longitudinally ribbed. 



