AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 223 



YELLOWSTONE RIVER SYSTEM. 



Yellowstone River 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 River 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 Kiver, Amethyst Creek, Soda Butte Creek, Blacktail Deer Creek, Lava Creek, 

 Glen Creek, and Gardiner River. 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; 

 Fish 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. It is the largest lake so near the summit of the Rocky - 

 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 he 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 larg er body of water which formerly filled Hayden Valley and 

 extended down the Yellowstone nearly to the present falls; but there is, I 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 ne,ed 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 



