


THE SYLVA OF MONTANA. 417 
Idid not find them I have no doubt of their identity, hav- 
ing seen the specimens. It is somewhat singular that all 
the fresh-water mollusca I found in the Misioni, above Fort 
Benton, were distinct species from those obtained by Dr. 
Hayden in the streams east of the mountains (except Unio 
luteolus and Physa heterostropha), thus showing that the 
limits of the region apply to animals as well as plants. The 
rest were Tiu palustris, bulimoides and desidiosa, Sphe- 
rium striatinum and Margaritana falcata Gld. Dr. Hayden 
found thirty other species in Nebraska. 
Kootenay region. — My observations last summer confirm 
the-propriety of this division of the north-western province 
(Caurine) , being defined towards the south essentially as I 
marked its limits in the Smithsonian Report of 1858. It 
consists, south of latitude 499, chiefly of the elevated basin 
of Clark's Fork, with the mountains which surround or 
traverse it, nearly all being more than 2000 feet above the 
sea (about 4000 feet where we crossed the Bitterroot), and 
from that ao up to perpetual snow at probably a level 
of 10000 fee 
Though, as ae by the accompanying notes, the western 
rim of this basin presents many marked differences from the 
portion east of the Bitterroot crossing, analogous to those 
between the Coast and Cascade Ranges farther west, I can- 
not now consider them distinct regions, but as united by the 
common character of being almost completely wooded. This 
character must also annex to it the lower country along 
the Spokan and the Columbia above that tributary, most of 
Which is, however, so mountainous as to reach as high as the 
basin of Clark's Fork. The woodless portions of this region 
Were small in extent along our route, being limited to the 
Porous, dry tertiary and lluvia basins of Deer Lodge and 
St. Mary's valley, with small tracts in the valleys connecting 
, and brauching from them. The most extensive prairies are 
of our route, towards the heads of these valleys, with 
^ connected valley toward the ies on Flathead river. So 
; AMER. NATURALIST, VOL. III. 
