AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 
223 
YELLOWSTONE RIVER SYSTEM. 
Yellowstone Biver drains all the eastern and northern side of the National Park, 
more than half its area, and from these waters much the larger part of our collections 
was taken. Yellowstone Lake was visited both years; Pelican Creek and smaller 
tributaries at the northern end were searched; and Yellowstone Biver was examined 
at intervals from the lake to the mouth of the Lamar or “ east fork.” The smaller 
tributaries of this system examined were Alum Creek, Tower Creek, Slough Creek, 
Lamar Biver, Amethyst Creek, Soda Butte Creek, Blacktail Deer Creek, Lava Creek, 
Glen Creek, and Gardiner Biver. Collections were also made from numerous lakes 
and ponds connected with this drainage system: Duck Lake near the west bay of Yel- 
lowstone Lake; some alkaline ponds near Baronette’s Bridge across the Yellowstone; 
Pish Lake, near the Soda Butte; Twin Lakes, on the flat dividing the head waters 
of the Gibbon from those of the Gardiner and drained by Obsidian Creek; Lake of the 
Woods; Swan Lake, draining into Glen Creek; a small lakelet near Mammoth Hot 
Springs, connected with the Gardiner; and Boteler Springs, outside the Park. 
Yellowstone Lake . — With Yellowstone Lake we reach the aquatic headquarters of 
this region, the real center of interest and importance for the study of the inverte- 
brate life of Yellowstone Park. Lt is the largest lake so near the summit of the Bocky 
Mountains, and, excepting its high altitude, presents every feature suitable to the 
maintenance of an abundance of animal life. Its zoological interest is fittingly sup- 
ported by its geographic and scenic features, which supply an admirable setting to 
the picture of life that slowly shapes itself in the mind of the zoologist as lie studies 
its waters and their contents and the inhabitants of its bottom and shores in their 
relation to each other and to surrounding nature. 
The geology of the region shows that the present lake is only the relatively small 
remnant of a much larger body of water which formerly filled Hayden Valley and 
extended down the Yellowstone nearly to the present falls; but there is, 1 think, no 
reason to believe that it has dwindled in zoological importance as it has in size. 
Except for changes of climate, the variety of animal forms a lake of this size may 
maintain need not be surpassed (and commonly is not) by that to be found in one 
many times its size. It is not likely that there was ever here, when this lake was 
largest and deepest, a special interior and deep-water fauna, such as occurs, for 
example, in the Great Lakes of North America; for, if there were, remnants of it 
would certainly continue and would have appeared in our deep-water dredgings. 
As a home of animal life it has probably been for ages similar to what it is now, 
except that we must suppose that the single species of fish which now inhabits it — 
evidently an immigrant across the continental divide — has produced certain changes 
in the balance of life, some of, which will doubtless become more apparent as our 
collections from this lake are thoroughly studied. 
The most striking feature of Yellowstone Lake is the irregularity of its form and 
the consequent length of its shore line, such that with an area of about 140 square 
