AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 2 1 1 
On August 30 we closed the field work of this trip with collections from Glen 
Oyeek below the falls, from the Gardiner Biver at the mouth of Hot Creek, near Mam- 
moth Hot Springs, and from a small lakelet among the hills, towards Gardiner. 
The accumulations of the trip were made under 387 collection numbers, represent- 
ing 43 localities. 
Our work was limited substantially to the central park plateau, only that about 
Mammoth Hot Springs passing beyond the lava formations which cover the plateau 
everywhere to an unknown depth and noticeably affect, as we discovered, the animal 
life of its waters. The river systems investigated were those of the Gardiner, the 
Madison, and the Yellowstone, on the Atlantic side of the “ continental divide,” and 
of the Snake on the Pacific slope. The principal fishless waters examined were Sho- 
shone and Lewis lakes, the Upper Gibbon and connected waters, the Firehole and its 
branches, Goose Lake, Twin Lakes, Swan Lake, and Tower Creek. The effects of 
geyser and hot-spring outflow were shown especially by collections made from the 
Firehole and from Alum Creek; and those of the occurrence of falls in the course of 
these mountain streams were shown especially by collections from the Gibbon and 
some of its tributaries. The highest elevation represented by our aquatic material 
was that of Mary Lake (8,200 feet) and that of a small lakelet near Norris Pass, 
not far from the same level. The greatest depth at which we dredged was 195 feet 
in Yellowstone Lake, although this depth was exceeded somewhat in the work of 
the following year. The altitude of this lake is 7,740 feet above the sea. 
As material for a study of variations in biological condition, we obtained an 
abundance of specimens for a comparison of the system of life in lakes, ponds, rivers, 
and creeks where no fish are found with those in which only a single species occurs, 
and with those supporting from three to eight kinds of fishes. 
The effect of the “continental divide” or watershed upon the distribution of 
aquatic animals is, of course, amply illustrated by our material; and this, taken in 
connection with materials gathered the following year from lower altitudes, should 
show something of the limitation of range of several species imposed by differences of 
elevation and the like. The influence of widely different geological conditions should 
likewise become manifest as we compare the animals of the waters of the Park 
plateau with those outside. 
My warmest thanks are due to Capt. F. A. Boutelle, acting superintendent of 
the Park, who encouraged and aided our investigations in every possible way, and 
to our guide, Mr. Elwood Hofer, whose tireless energy and active personal interest in 
our operations were greatly in our favor. He was not only the guide and manager of 
our movements, but a most efficient volunteer assistant in camp and in the field. 
