AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 
231 
GARDINER RIVER SYSTEM. 
Twin Lalces . — 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 River 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 Coretlira larvae. 
A surface haul under the same conditions gave a few examples of Daphnia schoedleri , 
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 fish — were the commoner insects ( Notonecta , Hygrotrechus , ephemerid and 
agrionine larvae), several specimens of Gammarus , a great quantity of the entomos- 
tracan Sida crystallina, and a few Simocephalus vetulus 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 mountain 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 Char a 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- 
