28 BULLETIN OF THE 
Columbia River 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 Jand 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 found on the banks of the river below the Cascades. Very 
likely the original strigosa 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 striz. C. Shell 
longitudinally ribbed. 
