AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 211 



On August 30 we closed the field work of this trip with collections from Glen 

 Creek below the falls, from the Gardiner River 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- 

 shoneand 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. 



