AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 231 



GARDINER RIVER SYSTEM. 



Turin Lakes. Collections were made August 20 from the upper of two small, 

 closely connected lakes called the Twin Lakes, lying in the boggy trough between the 

 hills beside the main road from Mammoth Hot Springs to the Norris Geyser Basin. 

 This and the two following lakes belong to the Gardiner Eiver system. The Twin 

 Lakes give origin to a small stream known as Obsidian Creek, through which they 

 are connected with a great expanse of swamp and shallow weedy water, known as 

 Beaver Lake. The upper lake is a clear, clean-looking pool, with much marginal 

 vegetation (lily pads and the like), and with boggy banks which drop off suddenly, 

 forming an overhanging grassy margin. Several discolored springs open into the 

 lake, discharging into it water which is said to contain alum in solution. 



The dredge brought up from the deepest water found (beginning at 30 feet and 

 ending at 39), a quantity of very soft, streaked, ill-smelling mud, with a little dead 

 vegetation and a very small proportion of animal life. This consisted mostly of Chiron- 

 omus larvae, partly red, but most of them faded brown, as if discolored by their 

 surroundings. The only other product of the dredge was two specimens of Gamma- 

 rus, a single leech (Clepsine), and one Pisidium. The water itself, however, was well 

 stocked with animal life, and a haul of a towing net above the bottom, at a depth of 

 30 feet, at 11 a. m., in bright sunshine, with a stiff breeze blowing, gave a consider- 

 able number of Gammarus, a very good collection of the characteristic entomostracan 

 of this lake (Diaptomus lintoni), and several specimens of Daphnia and Corethra larvae. 

 A surface haul under the same conditions gave a few examples of Daphnia schcedleri, 

 an occasional Cyclops, a single ephemerid larva, and a large quantity of Diaptomus 

 lintoni. Alongshore, upon the weedy bottom an admirable lurking and feeding 

 ground for lish were the commoner insects (Notonecta, Hyyrotrechus, ephemerid and 

 agrionine larvae), several specimens of Gammarus, a great quantity of the eutomos- 

 tracan Sida crystallina, and a few Simocephalus vctulus and Chydorus. Curiously, not 

 a caseworm was taken from this lake a fact possibly to be explained by the peculiar 

 character of its bottom. A careful search was made from the boat and along the 

 bank for signs of a plant of monntaiji whiteflsh made here the preceding year by Mr. 

 Lucas of the U. S. Fish Commission, but no trace of them was found. 



Swan Lake. This lake, a quarter of a mile long by two thirds as wide, is of nearly 

 the same size as the two preceding, but is, perhaps, the shallowest of all (not over 

 3 feet in depth). It lies on a plateau of the same name, not far beyond Terrace 

 Mountain and beside the main Hot Springs and Geyser Basin road. Its waters are 

 derived from the adjacent mountains to the west, and pass out through Glen Creek into 

 the Gardiner. As it lies in a plain, its immediate surroundings are level. Its bottom 

 is of rock and sandy mud, with Chara and other weeds, and a strong growth of rushes 

 inshore. 



The collection lists from this little lakelet are unusually full, a fact apparently 

 due chiefly to its geological surroundings. All the waters previously discussed are 

 situated in the Park plateau, and the rocks of their drainage basins are all lava in 

 some form, usually that modification of it known as rhyolite. Swan Lake, on the 

 other hand, is in a cretaceous region, where the geological deposits are largely lime 



